Chapter 4: The retornados and their "roots" in Angola. A generational perspective on the colonial past and the post-colonial present A sketch of the field of investigation, Lisbon, May 2013

This year, the Africa Festival, including a celebration of Africa Day, is being commemorated in Portugal throughout the whole month of May.

24 May, in Lisbon, at the Teatro do Bairro: I am watching a performance called The Last Message of Amílcar Cabral to the people of Guinea-Bissau and Cape Verde. Some images from documentary films depicting the Portuguese presence in Africa are being projected in a very dark room. Pictures of a family of Portuguese settlers living in a hut are repeated over and over again-they are lost in the depths of Africa. A message is vigorously hammered home for several minutes by one of the performers, a Cape Verdean who describes himself as a political activist: "Decolonise your minds! Decolonise your minds! Decolonise your minds!" The few spectators are young: a dozen people, including a couple comprising a child of retornados and a young Portuguese-Angolan woman.

25 May, Rossio Square: The Community of Portuguese-Speaking Countries, the CPLP, is being celebrated by several hundred people and by associations of migrants from Cape Verde, Guinea-Bissau, São Tomé, Angola and Mozambique, as well as some Portuguese families of retornados: they are all dancing. On the sidelines of this celebration of an Africa that is simultaneously "authentic" and "Lusophone", a group of young Afro-descendant activists are denouncing the neo-colonialist ideology of Lusophony and racism in Portugal.

Forty years after the independence of the African colonies, with the repatriation of nearly five hundred thousand retornados at the end of what is referred to as the Colonial War, and then followed by postcolonial immigration, a noticeable multiplicity of narratives on various aspects of the historical experience of (de)colonization has emerged in Portuguese society. Critical voices have arisen within civil society, and within the research community. Some want to escape from the illegitimacy and the silences surrounding the topic of decolonization; others want to denounce a post-dictatorship society without memory, or even the racism of postcolonial society.

The following reflection looks at contemporary relationships with a painful past (Stora 2005), within a dual socio-anthropological perspective. On the one hand, the focus of interest is on the social conditions of reconstruction and expression of "memory"; on the other, it takes into account the ways in which traces of the past are mobilized and reappropriated and may, from an individual perspective, even define existence (Jackson 2013).

The aim is to analyse the plurality of individual and family narratives told by the retornados, using a generational perspective: one made up of individuals born in Angola in the decade 1930-40; another made up of their children, also born in Angola, and Elsa Peralta (ed.

repatriated as children or adolescents; and yet another made up of individuals born in Portugal after 1975. This analysis is based on ethnographic research surveys carried out since 2012 in Portugal (Lisbon, Almada, Amadora, Évora, Caldas da Rainha), Angola (Luanda) and Brazil (Rio de Janeiro, Belo Horizonte) with about thirty individuals and their families, all closely linked to the history of the Portuguese presence in Africa, mainly in Angola. 1 The present study focuses on seven Portuguese settler families that were rooted in Angola for longer than a single generation. 2 These decolonization migrants arrived in Portugal more often than not without family networks to draw upon; they were also characterized by a large number of racially-mixed marriages, often dating back to before the 1930s (and before the Colonial Act of 1930). This mixed racial heritage is not always phenotypically visible in the third or fourth generations, precisely the people we are interested in here. These family trajectories also illustrate the difficulties and limitations of analysis in terms of "white retornados" and "non-white retornados"; the latter could also be included in the political category of "white Angolans", or "Euro-Africans" 3 . This compels us to question historically-constructed racial stereotypes, that researchers must be careful not to reinforce.

As far as I am aware, Stephen Lubkemann's research is unique in taking an interest in how the retornado population was "internally differentiated " (2002; 2003). He shows how at least three factors-race, class, and strength of family ties in Portugal-"affected the ability of retornados to negotiate their social position and identity in Portuguese society" (2003, 76). Using the metaphor of "internal strangers" to designate the retornados upon their arrival in Portugal, 4 he identifies "the salience of the race as a pivotal factor" in their not outgrowing this status of "internal stranger": "The atrophy of the label of retornado in public discourse has not translated into the treatment of this minority as 'Portuguese', but paradoxically has resulted in their increasing conflation with other populations of African origin (…) " (2003: 92). Although I have been influenced by Lubkemann's work, my approach comes from a different perspective. What has attracted my attention is the question of the relationship to the past, and the constant 1 This research, which was initiated as part of the FCT postdoctoral project "Legados contemporâneos do colonialismo na sociedade portuguesa pelo prisma das migraçoes" (SFRH/BPD/72232/2010), is part of a larger project, "Disrupted Histories, Recovered Past" (2016-2019), jointly developed by the Arts and Humanities Research Council, Care for the Future section (Swindon, UK), and the Laboratoire d'excellence (Labex), "Passés dans le Présent" section (Université de Nanterre), directed by Sian Sullivan (Bath Spa University) and Michèle Baussant (CNRS). 2 Quoting Gerald Bender (1978), Lubkemann suggests that 30% of the European population in Angola extends back more than one generation (2003, 79). The number of "retornados of African descent" who arrived in Portugal between 1975 and 1981 has been estimated at between 25,000 and 35,000 (Baganha and Gois 1998-1999, 260): "a figure possibly amplified if we consider the fact that many of those of mixed racial descent would be likely to be classified as 'black' at least in terms of the way they would be treated in everyday interaction within Portuguese society" (Lubkemann 2003, 89). This category of "retornados of African descent" is problematic because it refers to socio-historical realities of (de)colonization which are diverse.

3 "(…) a significant number of mixed-race people joined Euro-African nationalist movements. They were mainly the children of colonists (usually the children of white fathers and mixed-race or black mothers) who, because of their fundamentally European background and socialisation, were more integrated into the social stratum of the coloniser (white) than into the social stratum of the colonised population (black)" (Pimenta 2008, 19); see also Messiant (2006). 4 "(…) the fact that for retornados the grounds for exclusion as 'internal strangers' were 'performative' rather than 'essentialized'-seen as the product of voluntary choices rather than inherent essences-opened up the possibility of challenging this status over time through counter-performances that could reestablish their public commitment to community and family" (Lubkemann 2003, 84). updating of links with the "lost territory". Through the "returnings"5 to Angola that are happening today in the context of professional projects, returns that also take the form of journeys of memory and of identity (Dos Santos 2016; 2017a), the research reveals a continuity in the present and in the future of the retornado past, at both the individual (descendant) and social levels. 6 These "returnings" are also sometimes detours. Indeed, in Portugal some of these youthful Portuguese7 realize that the society that they live in is fractured by its colonial past. This raises the question for some of these children of former "internal strangers" (Lubkemann 2003) in Portuguese society, of where do they belong, and of their identification with the "outsiders" of today-those who have arrived since the 1980s as immigrant labourers (Machado 1994; 1997) from the former Portuguese colonies.

"We left civilisation behind when we left Angola." 8 On the love for Africa and rejection of Portugal: personal narratives of two generations

The memory analysed here is above all the personal and intimate domain of remembrance conjured up in family spaces in the presence of the researcher. 9 In some cases, this past is shared in particular circumstances, such as retornado gatherings, and this draws our attention to the effects that belonging to a collective has on memories preserved by individuals (Lavabre 1994).

At this stage of the research, it is not possible to develop a typology of all the collected life narratives. Such a typology would simultaneously take into account the length of the family's presence in Angola, the social groups that they belonged to (professional, political) and possible racial classifications, gender, as well as the experience of repatriation-or "exile"10 -and reintegration into Portuguese society. It is possible, however, to classify the narratives by generation, and according to the links maintained or reconstructed with Angola since the repatriation in 1975.

As such, this chapter presents a dialogue between the narratives of two generations, one made up of individuals born in Angola in the decade 1930-40, and the other made up of their children, also born in Angola, and repatriated as children or adolescents.

The impossible Return of the "second-class portuguese"

The common thread in the stories collected from men and women born in Angola between 1930 and 1940 is above all the chronology of family narratives: the emigration of ancestors-the great-grandparents in the late nineteenth and early twentieth centuries-and family ties with and marriages to local black or mixed-race women: "that's how Angola was made." 11 There is also the question of the vast resources of the territory (diamonds, oil, timber), the multiplicity of possessions that were acquired (houses, businesses, cattle ranches), and the professions practised by each family member. In general, few details are offered about why they were in Angola, or on colonial emigration, and nothing on the living conditions at the "beginning" of their settlement. This shows that links with the colonial metropole were almost non-existent. These narratives relate "ordinary destinies" (Haegel and Lavabre 2010), and in this way, as narratives on genealogical rootedness they constitute a performative statement of territorial legitimacy.

Individuals of this generation represent themselves as protagonists in a collective history that is more about family or community than nation. It is a history of a venerable and natural presence in Africa, which was not supposed to be interrupted, at least not in the way that it happened. Indeed, while the idea of an independent Angola is often mentioned, it is an independence in which the "true men of Angola", "white Angolans" (Pimenta 2008), would have seized power following the logic of a system of colonial autonomy as in Rhodesia. 12 A comparison with other types of colonization is brought up in the stories. Apartheid South Africa is sometimes mentioned as a contrast to the Portuguese colonial model, which is considered less violent. 13 There is, however, a criticism of the Portuguese model, namely, the plundering rather than the development of Angola, a theme that is mentioned by mixed-race Portuguese families who stayed on after independence, as well as by some recent Portuguese migrants in Angola (with Angolan roots) (Dos Santos 2016).

For some, who became "second-class Portuguese" for the colonial administration-starting in the 1930s, in the context of a state policy of social and racial discrimination (Messiant 2006)-the feeling of rejection by the metropolis has left its traces. Although not obvious, this feeling is manifested through the expression of a strong sense of belonging in relation to Angola: (…) a segment of the white population began to believe that it was the objectperhaps even the "victim"-of Portuguese colonialism and no longer one of its agents. As a result, the metropolis came to be seen as "other" by the settlers. Their degree of political identification with Angola increased exponentially, so that they began to build their sense of nationality with their backs turned towards Portugal (Pimenta 2008: 429-430).

11 Interview with a cattle-breeder and trader who was born in Angola, in Sá da Bandeira (which became Lubango after 1975) in the late 1930s (the first city name mentioned is the one used by my interlocutor, a comment that applies to the rest of the text). His mother was the daughter of a mixed couple, "a pure white man" from Douro and a "black woman" [preta]. For more on such marriages and the complex character of race relations in Angola, see Barbeitos 1997. The terms Preto/a [Black], Branco/a [White], and Mulato/a [Mullato] are used here as social constructs that are based on the racial stereotypes inherited from colonialism. 12 For a detailed analysis of Euro-African nationalism in Angola-nationalism in the sense of being anticolonial and pro-independence-see Pimenta 2008. The comparison with Rhodesia reveals, in the Portuguese model, the very weak political integration of the colonists in the government of the colony. 13 See Castelo 1999.

For these families, rooted in Angolan territory for several generations, the return to Portugal was ontologically impossible. The theme of leaving Angola appears often in the stories of these adults, parents of young children in 1975, but not in the narratives of the children themselves (analysed below). The story is gendered: the women describe the loss as associated with the intimate family sphere, with domestic life: "Everything stayed there ... a life!". In turn, the men meanwhile talk of economic activity: "The year before all blew up we bought cattle in Sá da Bandeira". 14 The violence of their forced departure from Angola and the exclusion that they experienced before and after 1975 were obstacles that were overcome over time and within the intimacy of the family. The long-term impact on their sense of belonging is an issue that has not yet been sufficiently addressed in the research conducted on retornados as a differentiated population. The experience brings back negative memories, a feeling of illegitimacy that is simultaneously social, racial, and to do with citizenship.

In these families, what is evoked is not so much exclusion and loss, but rather an ongoing sense of an origin that has lost its legitimacy. Continuity is constructed through the recollection of memories, and memory building is based on lived and/or transmitted experiences. Social and cultural practices-culinary as well as religious15 -are superimposed on the remembrance of past experience, and (re)constructed in the social context of Portuguese society, linked to the former colonies through the movement of people and cultures-including members of transnational Portuguese families. 16 Memories and practices are shared at regular meetings of retornados-for example the "Inseparables of Huíla"17 which has met every year since 1978, or others which discreetly reproduce African practices of socialisation. 18 Such events constitute social spaces for the construction of a memory of exile, not merely nostalgia for a lost past (Baussant 2002; 2016).

Meetings with relatives who are scattered across different countries offer other opportunities to share memories and to update the past, especially for families-often the same ones-whose members travel between Portugal and Angola and between Portugal and Brazil. They are occasions where the present moment can be brought to mind, recent news from family members who are still in Angola can be shared and the political situation can be discussed. They also provide an opportunity to evoke Angolan customs: traditional ceremonies such as those connected with betrothals [alambamentos] or the celebrations and music at funerals. These are examples of a paradoxical fascination with, and an "exoticisation" (Saïd 1978[2005]) of, a culture. It is composed of both a close identification with and a distancing from a country that no longer belongs to them.

The moral condemnation of the colonizer that was levelled at the retornados in Portugal 19 became explicit in the interviews that were carried out at reunions with relatives who had opted for exile outside Portugal. These narratives were recounted by a multiplicity of voices, and constituted confrontations with a range of experiences, highlighting aspects that were often forgotten when I asked the same interviewees and their children about reintegration into Portuguese society: the collective (negative) imagination around the phenomenon of the retornados and the political context of the period, along with their refusal to live in a country that was "in the hands of the communists". 20 The meetings also produced a narrative of an imperial territorial continuity, through comparisons made between Brazil and Angola:

The greenery is the same in Brazil. The air smells the same, the atmosphere, and the smell of nature. It's the green smell of the plants that you meet when you get off the plane after ten or twelve hours. 21 This sharing of "sensory experience" (Candau 2000) unites individuals and groups who see themselves as members of the same community, the Portuguese empire which remains present in their imagination (Silvano and Vilar 2015).

Finally, the narrative of loss becomes explicit when the return to Angola is brought to mind. After the end of the civil war in 2002, such journeys became more frequent, especially for members of transnational families who maintained links with the country since independence. These stories evoked "shame… and revulsion" in the face of the "filth and the disorganization": "This country used to be ours!" 22

"The Portuguese don't like africa!": Genealogical rootedness in Africa and the sense of otherness in Portuguese society

Maria Manuela 23 introduced me to her relatives, living in a quiet suburb north of Lisbon, on the occasion of a visit by family members who settled in Brazil after 1975. At that point in the research I had already met Maria Manuela several times, as well as her brother and some mutual friends. All of them had in common the experience of having lived in Angola and having been repatriated to Portugal during their childhood or adolescence. 24 19 Portuguese settlers, in the context of the Processo Revolucionário em Curso [Ongoing Revolutionary Process or PREC], were characterised as "agents of colonialism", and slandered in the predominantly leftwing press as anti-revolutionary reactionaries and minions of colonial oppression. See Lubkemann 2002;Ovalle-Bahamón 2003. 20 An anti-communist military dictatorship was in power in Brazil between 1964 and 1985. One interviewee who was repatriated from Angola in 1975 with his parents when he was eight years old, and then moved to Brazil, explained: "We weren't fascists, we left for economic reasons." However, my interviews in Brazil with Portuguese who chose to go into exile instead of "returning" to Portugal, reveal political and economic dimensions entangled in a Brazilian society characterized by an independence that was achieved without decolonization (Cahen and Dos Santos 2018b, 196). 21 Statement by a woman born in Angola in the early 1940s to a white father and a mixed-race mother. In 1975, she became a refugee in Brazil with her husband (Interview, Lisbon, June 2013). 22 Idem. 23 Physiotherapist, born in Angola (Huambo, called Nova Lisboa under colonization) in the early 1960s; her father was a cattle breeder (see footnote 169). She was repatriated to Lisbon as a teenager, and was married to another retornado (they later separated). 24 The group consisted of people in their fifties, characterized by a strong endogamy between retornados. They practice independent professions: restaurateurs, small traders, paramedics. The social status of their All the relatives shared long family histories in Africa, across three generations: parents, grandparents and great grandparents. It might perhaps be possible to reconstruct the family history from narrative fragments related to social background and professionowners of small commercial establishments, teachers, officials in public administration or public companies-but nevertheless, my interviewees rarely had a very clear idea of what their elders did in Africa. Some imagined that the men in their family were diamond smugglers "just like everybody else back then," but the history of colonization was never made explicit. When I asked them about several generations of their Portuguese family members having lived in Angola, their answers were extremely vague: "those generations were already here for a quite a long time…" 25 What is presented about Angola, therefore, is a genealogical memory rooted in the territory. This antiquity is closely linked to the relationships of their male ancestors, Portuguese white men, with African women: My great-uncles married black women or mixed-race women. On the female side of the [maternal] family, the women always married white men; 26 My maternal grandmother wasn't white, she was mixed-race… we were five brothers and sisters and we all had a different colour! 27 Such narratives are always the stories of male experience, and further field research is needed-with a focus on the relationship between gender, sexuality and race-mixingto explore the female subjectivities of women in mixed unions in this specific colonial situation (Stoler 1989).

One of the reasons why Maria Manuela decided to introduce me to her parents, is because she wanted her father to tell me about their filiação [affiliation], their ancestral connection to Queen Ginga, who lived in the sixteenth and seventeenth centuries. 28 Recounting this kind of narrative shows how important it is for these individuals to be able to demonstrate the antiquity of the presence of their ancestors on Angolan and even African soil (one of the grandmothers was from São Tomé), as well as the social prestige enjoyed by some of them. In this regard, Arlindo Barbeitos reminds us that this type of relation developed before the contemporary colonial regime dating back to the Angola of the slave trade, corresponded to "the way the old mixed-race and black bourgeoisie, and sometimes even the 'traditional' aristocracy, integrated or absorbed foreign influences that they thought were worth their attention" (Barbeitos 1997, 310). In other words, if mixed marriages are to be analysed from a viewpoint that allows for the interweaving of power relations in a given "colonial situation" (Balandier 1951), it cannot be reduced parents and grandparents in the colony was heterogeneous and ranged from trader to colonial administrator, an aspect that needs to be considered when analysing the loss of social status experienced as a result of repatriation, a feeling that seems to be stronger among individuals who belonged to the colonial elites. Unlike the retornados of African descent described by Lubkemann, these families did not live (or did so only temporarily) in the segregated suburbs [bairros sociais] of the great metropolis of Lisbon. 25 Fernando, about fifty years old, repatriated from Angola (Luanda) at the age of 14 in 1975; the mother and the maternal grandmother were both born in Angola. 26 Idem. 27 João Luís, about fifty years old, repatriated from Angola (Luanda) at the age of 11 in 1975. He is a grandson of anti-Salazar republicans, the son of a colonial administrator and a woman from the Cape Verdean elite (she died before 1975 and is buried in Angola). 28 See Heywood 2017. simply to the relations of domination between the colonizer and the colonized. 29 However miscegenation is here deployed within an ideological discourse on the non-racism of the Portuguese: in this case, the non-racism of their forbears. João Luís refers to the concept of lusotropicalism to explain to me how Portuguese colonialism differed from other kinds of colonialism (Castelo 1999). Even today, for the generation of children of the retornados who were born in Angola, this rhetoric of miscegenation constitutes an internalized narrative of colonial domination.

All of the interviewees speak of a "love for Africa", as a sentiment that will make them distinct from other Portuguese: "The Portuguese don't like Africa! (...) We had to make unbelievable efforts in order to fit in here". 30 The distinction between those who like and those who do not like Africa reveals an othering-"we" who carry within us some element of Africanness, and "them" -which is strongly felt in these narratives. This othering is linked to a cultural identity, a self-identification-or better, the construction of such an identification-with Africa. Although miscegenation is by no means always visible in the phenotype-and is subjective in any case-they do not describe themselves as mixed race and miscegenation is never mentioned as an explanatory factor for any personal experience of racial discrimination within Portuguese society. They consider the latter, incidentally, to be characterized more by a "racism of class" than by a racism of colour.

The feeling of otherness is expressed through the categories used for selfidentification: "I'm a Portuguese from Angola", "a white Angolan", "I'm an Angolan man/woman". These terms call to mind the location of identity for individuals who believe that they "belong" to different cultures. 31 It also expresses distancing from Portugal-which "doesn't like Africa!"-and the validation of the civilizing mission that the families participated in: "We left civilisation behind when we left Angola!" 32 This assertion must also be understood in the light of the experience of the urbanized Africa that had been the lived reality of half the retornados (Lubkemann 2003, 87) and for whom Portugal in 1975 was a "poor", "grey" country without highways or supermarkets: "There was already a Jumbo 33 in Luanda in 1966!" 34 Instances of American products that were banned in Portugal but permitted in Angola (Coca-Cola is a classic example) are often mentioned, as are the freer manners and the lighter censorship. This, however, is never connected to any explicit criticism of the political system of the Salazar-Caetano dictatorship. 35 29 This must call our attention to the complexity of the issue of miscegenation, both as an historicallysituated social practice and as an ideology that has taken on diverse forms in the case of the Portuguese colonial empire: see Vale de Almeida 2002; for the Angolan case see Messiant 2006. As pointed out by Manuela Ribeiro Sanches, certain concepts such as hybridity, syncretism, miscegenation, may lose their critical, emancipatory element, when travelling to other contexts (Sanches 2009, 16). 30 João Luís, see footnote 185. 31 A kind of "in-between situatedness" that does not always fit into ideas of "miscegenation" characterized by identities or fixed affiliations; see Laplantine and Nouss 2001. 32 João Luís, see footnote 185. 33 A supermarket chain. 34 João Luís, see footnote 185. 35 Nor are there any detectable traces of political socialization that would be linked to Euro-African nationalism (Pimenta 2008); however, a study of João Luís's social ties shows that among his friends is the daughter of a historical MPLA activist in exile in Portugal after the events, internal to the MPLA political party, of 1977.

For the individuals who locate their narrative within the long history of the Portuguese presence in Angola, Africa is rarely mentioned as a colonised territory. In the descriptions of social relations, there is no mention at all of a relationship of domination. On the contrary, we see, rather, an emphasis on the closeness of families to their "servants", and the role played in social assistance to local people by public companies, such as Diamang and others, is often mentioned.

The interviews with Maria Manuela and other individuals of her generation turn away from adult experience in favour of childhood: "It's hard to leave a country where one had a happy childhood". 36 The photographs that the interviewees showed me illustrate their desire to show positive memories of an ordinary life on ancestral soil, the conquest of which raises no awkward questions. These are images of family togetherness, of camping holidays, of hunting, as well as many images of African landscapes; but these images from family albums make no contribution to the construction of a collective memory that would challenge the nostalgic and acritical attachment to the past (Garraio 2016). This is also a memory that seems to counterbalance not only the biographical rupture of the forced departure from Angola, but also the family separations that followed. The families are scarred by the many breakups, divorces and separations (both in Angola and after the Return). Many of them left their dead behind, abandoned mortal remains that symbolise their links with Angolan soil: physical traces guarantee that the deceased are always present and connect different places (Lestage 2012). The separation is also geographical in character, as when brothers or sisters decided not to be repatriated to Portugal and instead left for Brazil or South Africa, either directly, or later, after the Return to Portugal. Others moved to Mozambique or Macau in the 1980s and 1990s. These families, scattered in countries that were formerly Portuguese colonies, with transnational links kept up between their members, are building a Lusotopy with an imaginary that is inherited from the history of the colonial empire, and which still needs to be investigated (See Cahen and Dos Santos 2018a).

The "Return" journey to Angola and the denunciation of the "Persistence of History"37 : the post-1974-75 generation Since the end of the civil war in 2002, Angola has gradually begun to attract Portuguese investment, and at the same time it has become a preferred emigration destination for qualified Portuguese expatriates (Åkesson 2016; Dos Santos 2016). In addition, the Portuguese who were repatriated in 1975 have sought to renew their ties with Angola, particularly with those family members who stayed on after independence. Economic and trade links have been re-established, taking advantage of kinship ties as well as other connections from colonial times (a former classmate, somebody's godfather who became a member of the MPLA central committee, and so on). During the 2000s, some Portuguese who were born there tried to acquire Angolan citizenship. These procedures resulted in return trips to birthplaces in order to obtain birth certificates [the assento de nascimento] needed to prove the right of "nationality by origin". 38 The process also impacted the younger generation, the children who had been repatriated at a very young age or were born in Portugal after 1975. Angolan citizenship had become desirable because the Angolan labour market provided opportunities for graduates, allowed for free movement of people between the two countries and obviated the need for lengthy procedures to get work permits.

At the beginning of the 2010s, the constant flow of emigration to the former colonies, although small in comparison with labour movements within Europe (Peixoto et al. 2016), attracted intense media coverage in Portugal, at a time when Angolan influence in the public sphere was also increasingly visible. This took the form of massive investment of Angolan capital in Portuguese companies (from 2006-2007) (See Oliveira 2015), the high-profile presence of Angolan elites in Lisbon, and the promotion of Angola as a new Eldorado by Portuguese politicians and entrepreneurs with partnerships in the country. These expatriates and migrants belong to a new generation of young graduates who saw a chance to improve their socio-professional mobility by going overseas for a short time. They also saw it as an opportunity for significant economic benefit, and a way of avoiding the subaltern experience with which European migration is associated in the minds of graduates from the Portuguese middle classes (Dos Santos 2016, 37), previously unaffected by structural emigration.

The handful of studies on the presence of Portuguese migrants in Angolaestimated in 2012 at between 130,000 and 150,000 people (Oliveira 2015, 117)-show that social relations between white expatriates and the Angolan black and mixed-race middle class are racialized, and that inequalities between Angolan and Portuguese employees are associated with colonial history, which is to say, with forced labour, suffering and submissiveness (Åkesson 2016, 276). 39 These studies shed light on the complexity of these postcolonial power relations, constituted by continuities but also by breaks with the past. This is illustrated by the example of migrants who do not belong to the expatriate elite, and who often live in conditions of great insecurity and vulnerability (Åkesson 2016, 276). Some of the young migrants and expatriates come from retornado families, and for them their presence in Angola has aspects of memory and identity (Dos Santos 2016). It drives their search for material traces of places associated with a past family life, and the reconstruction of intergenerational memories:

When I found the house, it was in good condition, it had been well restored. It was occupied, people were living there… a couple. The wife was a bank manager there in Cuito and the husband was an officer in the army. I saw the house from the outside, I knocked on the door to visit, I had photographs with me … The husband was out, it was only the wife, and she seemed a bit anxious, she didn't really know what to do. I said that I was born there, that I was curious … Anyway, she phoned her husband, and he said that now the house belonged to them, and a long time had passed … I agreed that the house was theirs, I was just curious, that I was born in the house, but he said no, he wouldn't let me come in … (…) who have not regularised their situation, may no longer acquire Angolan nationality, and lose their claim from the date for publication of this law" (Diário da República, 27 March 2017). 39 See also Oliveira (2015, 120). On the category of "expatriates" in the context of professional mobility from the countries of the Global North to Africa, and the ethno-racialized debate with which it engages see Quashie 2016.

I spoke to them [the parents] once a week, on Sunday evening, and he [the father] answered the telephone and began to talk at length in Umbundu. He always asked where I was living, where I was. At the beginning, I sent lots of photographs by post, and when I went there I showed them photographs of the house when it was my parents' house, as well as of the city and other places where I had been. My father talks with nostalgia, but at the same time he doesn't want to go back. He's old and he knows that this is a lot different to the country that he lived in at that time, it would be a big shock for him to come here nowadays… 40 Of the interviewees in Luanda who were the children of former settlers, some had roots going back generations, some had been repatriated when they were very young and had no recollections of their Angolan experience, and still others were born in another country, Portugal. These repatriated children do not intend to return to Angola to mourn a country that no longer exists; they belong to a different generation from that of Maria Manuela and her friends. An analysis of the narratives of migration/expatriation of this generation shows that they deploy representations transmitted through family memory, and then appropriate them. Nuno, for example, states that in April 2006 he was the first civil engineer from his company to go to Angola, when the company won construction contracts for public works "at a time when most Portuguese didn't want to go". He was then 32 years old and he explains: I always heard stories about Angola and I was always very curious, although my ideas were different from what I found when I arrived here … Because I grew up hearing nice stories about Angola, and because my parents lived here for so many years and spoke so well about Angola, I came with expectations, I planned to stay here for ten years! When I arrived, I saw that it wasn't the way I thought it would be, what I'd heard about; it wasn't that country any more.

Pedro's41 family was repatriated by the airlift in 1975; they had been in Angola since the early twentieth century, although he does not know the exact date when his maternal great-grandmother emigrated from the Minho region. 42 The family kept a "memory of the exile" (Baussant 2002) alive, with no plans to return, and participated in annual meetings of retornados until the death of his grandmother, in the mid-1990s. Pedro remembers: "I was 11 years old, I had no idea what racism or independence meant… I was 18 or 19 when it all hit me." That was in 2007, when he made his first trip to Angola, accompanying his mother for the first time to his place of birth. Apart from reuniting with a maternal uncle, for his mother the trip offered a chance to complete the task of mourning her father, who had died in an accident and was buried in Angola: "The memories haunted her". At the same time, she began the process of applying for Angolan citizenship, thus making it possible for her son subsequently to acquire citizenship by birthright.

For Pedro, the key element in this trip was his mother's position in relation to her past: "If she had been hankering after the past, I don't know how our relationship would have been…" He speaks of sharing a relationship with Angolan culture and with Angolans themselves: "We talked in Kimbundu… we ate street food… we discovered local food, not the food that the whites eat: I still can't eat the food that the retornados eat!"43 After a year, Pedro returned to Angola by himself, with a professional contract at a private university in Luanda. He describes this experience as traumatic, revealing a critical attitude towards the behaviour of the Portuguese. His criticism is made up of three elements. The first is their refusal to give up a longing for the past. Pedro emphasises the importance of his mother's refusal to adopt a nostalgic posture during their earlier return to Angola. Instead, she broke away from that relationship with the past, as the family had relived it at the various meetings of retornados. The past is no longer solely associated with an ordinary, happy life lived in Africa, as reflected in the narratives of retornados. The past has the political form of a system of colonial oppression, something that is ignored in narratives that implicitly claim that "the empire was a good thing".

The second element in Pedro's rejection of colonial continuities is economic, and has to do with the role played by foreigners, including the Portuguese, in the reconstruction of Angola since 2002. Foreigners, including international consulting firms, have participated directly in all the key sectors of the economy. The logic at work is an emphasis on the short-term: the Angolan authorities show almost no interest in technology transfer or the acquisition of knowledge (Oliveira 2015, 115-124). Pedro deplores the "economic predation" engaged in by many Portuguese joint ventures and their employees. He describes a system of individual enrichment based on the wastage of public resources, facilitated by local corruption and by real estate speculation: "The Portuguese take huge amounts of money, millions of dollars!" Pedro could have participated in the system, but he refused, and eventually, warned by his employers, he was forced to return to Portugal.

To these two elements of a refusal to adopt a nostalgic posture, and a critique of economic neo-colonialism, Pedro finally adds the racism of the Portuguese. He recalls his experience at parties where whites are a minority. Single expatriate men assume his complicity in the sharing of degrading, "dehumanizing" remarks about black women: "It's very common when you enter a place in Luanda, and if you're the only white man, another white man will come up to you and immediately start up a conversation like that…" He remembers the violence of his emotions when confronted with these racialized social relationships, and the continuation of racial hierarchy. When his cousins 44 came to visit him at his workplace, a private university, they were denied access to facilities such as bathrooms, the kitchen, and bedrooms that had been allocated to white teachers: When I tell this story to people from here, they don't want to hear it. They accept that you would have been traumatized, but by the racism of the blacks who are even more racist than we are! In Portugal, when expatriates and migrants talk about their experiences, it is quite common to hear about Angolan anti-white racism. The concept is also current in academic circles, and helps to mask the emergence of the question of race as a public problem in a society where the ideology of Lusotropicalism still retains its power (See Vala, Lopes and Lima 2008).

Is it possible to generalize Pedro's critical attitude to the persistence of these vestiges of colonialism? Narratives from other Portuguese of his generation of expatriates in Angola show awareness of an historicity-a collective meaning attributed to historythat they no longer share. Pedro recalls with astonishment the attitude of one of his colleagues in terms of his empathy for the black population: "He didn't react like a Portuguese, in fact he reacted very well!"

Plurality of memory and "public uses" in Portuguese society

In Portugal, the absence of reflection (a kind of unthinking) on the colonial experience (Lourenço 2014) led to a late emergence of the critical questioning of colonialism, in the academy (Castelo 2005-2006) as elsewhere. 45 Representations of the colonial past were extremely homogeneous: "Colonialism was not a subject that was discussed in polite society. As a general rule, opinion about of the expansion, the 'Discoveries' [Descobrimentos] and Portuguese colonialism was positive" (Castelo 2005-2006, 12). After 1974, the Portuguese state played a crucial role in maintaining this persistent and hegemonic historical narrative. 46 A "politics of the past" (Hartog and Revel 2001)-for example the establishment of the Comissão Nacional para as Comemorações dos Descobrimentos Portugueses [National Commission for the Commemoration of Portuguese Discoveries] in 1986-activated an "expansionist and imperial rhetoric around the reconfiguration of postcolonial identity" (Vale de Almeida 2000, 161). Since the loss of empire, Portugal has reinvented its place in the world through its "diaspora" (See Feldman-Bianco 1995; Caetano da Silva and Dos Santos 2009) and through the construction of a "Lusophone community" based on the idea of a reified human community (Cahen 1997; 2012) and on silence about the common past (Domingos 2016).

The colonial question was a theme in the Portuguese literature of the 1980s, particularly with regard to the Colonial War (See Ribeiro, 2004). However, the real break with the "long period of silence" (Valentim 2005-2006, 38) dates from the late 1990s, when multiple stories by ex-combatants were published. 47 The emergence from the shadows of a "colonial memory" based on the experiences of retornados dates from the 2000s. More inaudible than silent and marked by an illegitimacy of memory (Peralta, Góis and Oliveira 2017), these recollections found an echo in Portuguese society more than thirty years after the end of empire and the repatriation. Thirty years is sufficient time for a generation to reach adulthood. The bearers of memory are most often the children of the retornados. The transfer from a private family space to the public sphere was effected by the publication of numerous novels and biographies describing repatriation by airlift and nostalgia for Africa-"the promised land"-as well as 45 "The longevity of the dictatorship explains the weakness of anti-colonial historiography and the relative abundance of a hagiographic historiography of the Portuguese empire" (Castelo 2005-2006, 17). 46 The fact that the protagonists of the Revolution of 25 April 1974-the armed forces-had also been the main agents of colonial oppression has contributed to this silence (Castelo 2005-2006, 18). 47 On this question, see the work of M. J. Lobo Antunes (2015), anthropologist and daughter of the renowed writer António Lobo Antunes, who highlights the role played by young Portuguese researchers (anthropologists and historians in particular, working on their own personal narratives) in the collection and publication of these memoirs; see also Basto 2017. photographic montages posted on the Internet. The establishment of public historical websites and archival blogs shows how the Internet has played a role in publicizing and connecting narratives around the world, in Canada, the United States, Brazil, Australia, Portugal and South Africa. These social networks of memory need to be understood, especially if they are as diverse as one would imagine. 48 This context of memory is characterized by a homogeneous narrative describing positive aspects of life in Africa. According to Stephen Lubkemann, from the 1990s onwards some retornados would have taken on board the rhetoric of a Portuguese postpostcolonial identity that serves to validate their past experiences (Lubkemann 2002). Such narratives of nostalgia may have been associated implicitly with a condemnation of decolonization (Castelo 2005-2006), but above all they constitute an acritical and even ahistorical discourse: narratives of daily life in an ordinary context.

A break in the historicity of the Portuguese colonial and imperial past seems to have been slowly taking place in Portuguese society since the end of the first decade of the twenty-first century. It is apparent in literature, [START_REF]Among the most noteworthy examples are Figueiredo 2009 and Cardoso[END_REF] documentary film [START_REF]For an analysis of some of examples from this body of work, see Basto[END_REF] and the performing arts, in dialogue with researchers in the social sciences and humanities. 51 The break demonstrates the specific role played by the post-memory generation (Hirsch 1997), those who did not experience dictatorship, colonialism, the loss of empire, and the Return. [START_REF]postcolonial studies by scholars working on these issues, notably Maria Calafate Ribeiro in the projects that she coordinated: Children of the Colonial Wars: Postmemory and Representations[END_REF] For them, the connection with the past does not happen through memory but through imagination, articulating visions that are both intimate and distanced from the past. This is a post-memory of (de)colonization and return that is revisited via present experience, as in the case of Pedro.

These stories, both public and private, contribute to the building of a critical perspective towards the past, and reveal a "negative memory" (Rousso 1987) that has been "buried" (Basto 2012, 37). They demonstrate that a "taboo is beginning to fracture, to do with Portugal's relationship with its former colonies, the absence of any work on memory, on responsibility, on the political system that kept colonialism alive" (Basto 2012, 37). These narratives also pose questions on how to live together in the present, in a fractured post-colonial society, in which a hegemonic historical narrative has silenced in public space a plurality of social memories (Dos Santos 2017b).

At present, it seems to have become ever more acceptable "to campaign for memories" (Hourcade 2015) [START_REF]The concept of memory is both a category of analysis and a political category mobilized by the individuals and social groups on which we work[END_REF] and to question the diversity of actors-the State, associations, spokespersons and memory entrepreneurs-as well as the ways in which these memorial projects are understood. In 2005, thirty years after the end of the dictatorship, the civil society movement Don't Wipe Out Memory! [Não apaguem a Memória!] 54 was set up. Various memories, related to both contemporary and ancient history, all begin to assert themselves: slavery, dictatorship, colonization/decolonization, the colonial war/desertion and exile, emigration. Alongside these political claims to memory we find, more often than not, demands for public recognition (Gensburger and Lefranc 2017), and the founding of museums. An example is the establishment in 2015 of the Museu do Aljube: Resistência e Liberdade [Museum of the Resistance and Liberty], which is "dedicated to the history and memory of the struggle against the dictatorship and in recognition of the resistance in the name of freedom and democracy" 55 . The museum is housed within the walls of a prison in Lisbon where opponents of the dictatorship were imprisoned and tortured. Other municipal and national museum projects have been announced: a Resistance Museum in the old political prison at Peniche; a Discoveries Museum in Lisbon, provoking controversy about what it is to be called; [START_REF]and groups of people of African descent have emerged demanding an historical pluralism in which the academy, journalism, and civil society would begin to speak more critically and more openly. It is also important that a new museum should also reflect this wealth of problematizations[END_REF] as well as a memorial to slavery. This last is supported by the claims of Afro-descendant people, who denounce the racial discrimination that is the heritage of slavery and the colonial past, the invisibility of black people in Portuguese society, and institutional racism. 57 The phenomenon of a "return" to recent painful memories, has been observed in many countries after periods of latency lasting thirty to forty years (Stora 2005). The Portuguese case shows us how the political positioning of the post-1975 generationpost-dictatorship, post-colonization, post-war, post-repatriation-has allowed a critical distancing to emerge in relation to the "persistences of history" (Carvalho and Pina-Cabral 2004). In the families of the former retornados, the plurality of memories, which go beyond the affirmation of a nostalgic Africanness, and the links with the former colonies through ongoing personal and cultural exchanges, demonstrate that some children of retornados are not merely "passive recipients of a legacy from the past" (De L'Estoile 2008, 268). Is it possible that what we are seeing here is the disappearance of the idea of a "competition among victims" (Chaumont 1997) and a struggle over memory (Lapierre 2011) among the descendants of the former colonizers and the descendants of those who were colonized?

The problem of "returning" in connection with the phenomena of migration has given rise to numerous studies in the last ten years (seeMarkowitz and Stefansson 2004). The scare quotes here are intended to call attention to the fact that the idea of Return cannot be taken as a given, that not everybody understands it in the same sense, and that more in-depth research is needed to fully comprehend these experiences in a postcolonial context. See also[START_REF] Fabbiano | Expats, installés et pionniers: mobilités contemporaines, mondes sociaux et dynamiques postcoloniales des Français en Algérie[END_REF]

Unlike the French Pieds-Noirs, for whom the past is not a bearer of continuity(Baussant 2006).

The categorisation of these individuals is problematic. Some consider themselves to be more Angolan than Portuguese, but in other respects these identity choices vary according to class, phenotype and racial discrimination, living spaces and social interactions with "Luso-Africans"[START_REF] Machado | Luso-africanos em Portugal: nas margens da etnicidade[END_REF] or "Afrodescendants" and lived experience, especially the "return" to Angola.

8 [Deixámos a civilização quando partimos de Angola

]. 9 "Memory" is used here in the sense of narratives and evocations of the past, which should not necessarily be confused with memories of experiences lived or transmitted by individuals (Bloch

1995).10 This expression was encountered during the research in Brazil, and was used to express the impossibility of returning to a postrevolutionary Portugal which my interlocutors could not identify with.

See footnote 169.

For research carried out on the Terreiros of Candomblé in Lisbon, mentioning the presence of retornados among the initiates, see[START_REF] Guillot | Du mythe de l'unité luso-afro-brésilienne: le candomblé et l'umbanda au Portugal[END_REF]

Old settler families exiled in Brazil, Luso-Angolan families that stayed on in Angola after independence and came and went during the civil war, depending on the situation; they sent their children to study in Portugal, and some of them owned houses in both countries.

These were organised by an association with the same name, which officially had 750 members in 2013. Huíla is a province in southern Angola. Originally established in Buçaco, Portugal, the meetings took place for several years in the forest of Caldas de Rainha, Portugal, and lasted for two days, including photographic exhibitions of the Angolan past as well as of recent journeys, communal meals of Angolan muamba chicken stew, a Catholic mass, music concerts and dancing.

Maria Manuela, see footnote 181.

Carvalho and Pina Cabral 2004.

This was still possible until February 2016, when a new nationality law was passed that prevented "holders of foreign citizenship and their descendants born in Angola in colonial times from becoming Angolans." Indeed, "Citizens who are the children of foreigners, born in Angola before independence and

Nuno is a civil engineer, born in Angola (Cuíto, called Silva Porto under colonialism) in 1974 to parents who were themselves born in the country. He left at the age of nine months and emigrated back to Angola in 2006 (Interview, Luanda, November 2012).

Aged about 30, with a doctorate in history, born in Portugal after 1975. The mother and one grandmother were both born in Angola (Huambo, called Nova Lisboa under colonialism).

For example: muamba de galinha (chicken prepared with palm oil and served with manioc flour), a dish that has become very popular in Angola.

Maternal cousins, the children of relatives who Pedro classifies as "black" or "mixed-race". They live in Lisbon and came to visit him while on holiday with their grandparents in Huambo (formerly Nova Lisboa, but Pedro uses the post-1975 place names).


G G&an

G Daufky+

U Merinb

J.-P Labb

A Quemeraisd

Fouling during constant flux crossflow microfiltration of pretreated whey. Influence of transmembrane pressure gradient*

Keywords: mnu&ltratlon, whey; foulmg, mfrared and X-ray photoelectron spectroscopy, hydmdymumcs

Pretreatment of whey by mlcrofiltratlon (MF) has emerged as a necessary step m producing high punty whey protein concentrates In the MF of pretreated whey using a Carbosep Ml4 membrane (pore dnuneter 0 14 pm), proteins and calcmm phosphate aggregates were responsible for foulmg, which mcreased accordmg to the "complete blockmg" filtratron law and accounted for a progresswe decrease of the active filtenng area. An operating mode with dynamrc counter pressure (recuculatlon of the permeate co-current to the retentate), as opposed to static counter pressure, allowed lower overall foulmg, a longer time of operation and better protem recovery because of more evenly distnbuted fouling along the membrane tube. At shorter times of operation, fouhng was greater under higher transmembrane pressure (TP) , so that the less fouled areas under lower TP were forced to filter larger volumes and consequently became fouled more rap&y This involved a movement of the effective filtermg area along the membrane tube, as evidenced by the systematrc evolution of fouling heterogeneity as measured by mfra-red spectroscopy

Introduction

Ultrafiltration (UF) of whey for the production of whey protein concentrate ( WPC ) , which has high nutritional and functional properties

[l-3],
is the major process employed in mem-*Paper presented at the Int Conf on "Engmeermg of Membrane Processes", Gamusch-Partenkrrchen, Germany, May 13-15,1992 Y'o whom all correspondence should be addressed 0376-7333/93/$06 00 0 1993 Elsevrer Science Publishers B V All nghta reserved brane processing of food. The WPC produced still contains small amounts of residual fat and phospholipids which alter its functionality [ 4,5]. UF' performance during WPC production is altered by membrane fouling. Removal of the major components responsible for such a phenomenon, using pretreatment of the feed streams, has been suggested to overcome fouling. It was reported that ionic calcium participated m the fouling layer [6,7], and conse-quently its removal by sequestrates, ion exchange resins, dialysis and adjustment of pH followed by centrifugation [6-131 was one of the more successful suggestions for improving fluxes.

Removal of residual fat from the whey is based on the tendency of phospholipoproteins to aggregate under ionic calcium binding, pH change and heat treatment [ 141. It was further developed into an industrial process that uses microfiltration (MF) to separate the aggregated mass from the whey, resulting in a clear filtrate that can be further concentrated via UF to produce high quality, fat free WPC [ 151. An analysis of the operating parameters of an industrial MF plant was reported by G&an et al.

[ 161: permeability and protein transmission were not satisfactory owing to membrane fouling. This fouling was blamed on poor control of the processing variables of the aggregation step (i.e. whey temperature, calcium addition, pH change, heating and holding time) and of the MF operating conditions (i.e. MF temperature and transient operational pathway to stationary permeation flux).

Two variables that are most important for effective MF performance are high flow velocity and low transmembrane pressure (TP) The present work is aimed at acquiring more knowledge about the phenomena that govern membrane fouling during MF of pretreated whey. The influence of fouling evolution with time was studied, and special attention was paid to the role of TP heterogeneity along the membrane. Such studies led us to relate the hydraulic properties of the membrane to the structure and composition of the fouling layers, as analysed by IR and X-ray photoelectron (XPS) spectroscopies.

Experimental 2 1 Mzcrofzltration

The MF rig, as described in detail by Daufin et al. [23], was equipped with a single Ml4 membrane tube (Tech-Sep, Miribel, France), which is a composite membrane made of 0.14 ,um mean pore diameter ZrO, filtering layer on a carbon support (6 mm inner diameter, 1.2 m long; 2.2 x lo-' m2 membrane area). The rig enables MF to be performed in two different modes: static counter pressure mode (SCPM), in which permeate compartment pressure is maintained constant, and dynamic counter pressure mode (DCPM) , which consists of circulating the permeate co-current to the retentate in order to create a permeate pressure drop equal to the retentate pressure drop, thus producing no TP difference along the membrane's hydraulic path. Owing to an imperfection of pressure drop regulation with DCPM, MF experiments were performed with a small TP gradient from the inlet of the filtering tube to its outlet, 7!P, -TP, = -0.2 bar. However, the TP gradient was smaller than that with SCPM (+0.6 bar).

MF was carried out with pretreated whey. Aggregation of residual fat in sweet whey from Emmental cheese was performed by a procedure adapted from that originally proposed by Fauquant et al. MF experiments, using a new membrane and a fresh batch of pretreated whey in each operation, were performed at 50 + 2 o C with a mean tangential flow rate (u) of 6.0 + 0.1 m-set-' and a mean retentate pressure (P,) of 4.0 ? 0.1 bar, with an initial pressure drop along the tube of ca. 0.5 bar. The permeation flux (J) was raised to a set value of 64 + 2 l-hr-'-m-2 at a rate of 10 l-hr-'-m-2-min-1, and the stationary volumetric concentration ratio ( VCR) was chosen to be 5 by running a feed and bleed system: retentate was extracted as soon as a VCR of 5 had been achieved at the appropriate flow rate as referred to the permeate extraction flow rate. The mean residence time of retained species in the retentate compartment was around 280 min. Operating duration ranged from 1 to 5 hr.

After rinsing the membrane with water, the pure water permeability was assessed by measuring the TP at three levels of J: 20,40 and 60 l-hr-1-m-2 (operating conditions: DCPM, u=4.0 m-set-', P,=l.O bar, T=50"C).

The slope of a plot of J versus TP gave, according to Darcy's law, the hydraulic resistance of the membrane: for a clean membrane R,, and with irreversible fouling R+ The total fouling R, was calculated from TP measured during MF, and reversible fouling Rd as described by Daufin et al. [7].

Transmission

1 Analyses

During MF, permeate and retentate samples were withdrawn for analyses of total nitrogen matter (NM), determined according to the Kjeldahl method and expressed as protein (NM x 6.38)) and of calcium by atomic absorption (Varian SpectrAA 300, Springvale, Australia) as described by Brule et al. [ 241. Transmission (Tr= 100 x C,/C,) was assessed assuming that the permeate compartment was a perfectly stirred reactor [ 251, and the relative experimental error was evaluated to be ca. 20%. Additional analyses were performed on the feed streams, on the supematant and on the sediment of centrifuged pretreated whey (2000 g; 15 min; T=30"C) (Table 1): optical density (OD) at 600 nm (Beckman DU 62, Gagny, France); phosphorus, by mineralization and calorimetric determination following the AF-NOR norm No NF V 04-264 [26]; a-lactalbumin and /I-lactoglobulin by reverse phase high performance liqmd chromatography according to a procedure adapted from Jaubert and Martin's work [27]. For the separation, elution was achieved using a linear gradlent from 49 to 64% of solvent B for 15 min. Fat content was determined by the method of Folch et al. [28]; proteins, phosphates and lipids were determined by infra-red spectroscopy (see Section 2.3.2) on freeze-dried samples.

2 Cakulatrons of "free"protein transmikon versus kme

The transmission of "free" proteins (not linked to calcium phosphate aggregates [ 141) Trf, was calculated as follows:

Tr f= Trexp -XTr, l-x (1)
where Trex,, is the transmission of total proteins, determined experimentally; 7'~~ is the transmission of proteins linked to aggregates, and assumed to be equal to the transmission of aggregated calcium. The concentration of aggregated calcium was determined from the experimental total calcium concentrations and from the percentage of aggregated calcium. The latter was computed using an interative procedure on the VCR calculated from a mass balance:

VCR= (~-TFc,)CF 1-Tr,,CF (2)
where Z'r,, = transmission of aggregated calcium ( % ) ; CF = concentration factor of aggregated calcium. In eqn. (1) , x is the ratio of linked protein concentration to total protein concentration; the linked protein concentration was 1.5 times the concentration of aggregated calcium in the initial pretreated whey. The figure of 1.5 was assumed to be constant throughout the MF run.

Models of selectu.Gty

The analysis of solute and solvent transport through capillaries according to sieving and the Poiseuille flow model allows the calculation of the transmission corresponding to a given membrane pore size [ 291.

The Poiseuille flow model is considered to correlate solvent flux and pore radius F as follows:

(3) where p is the dynamic viscosity of the permeate (the solution passing through the pore ) and I is the equivalent length of the pore.

The model used for solute transport, taking into account the ratio of molecule radius (r,,J to pore size (as initially proposed by Ferry where M is the molar mass. Table 2 gives the molecular radms calculated from the molar mass for the main four whey proteins, and their concentration in the feed whey needed for the calculation of protein mixture transmission.

Assessment of fouling 2.3.1 Fouling models

The decrease in permeability was modelled according to four filtration laws presented and analysed in relation to the performance of filter media by Grace [34]. The mathematical expressions of these models were established for filtration experiments performed at constant permeation flux.

(i) Filtration in which membrane properties (surface, resistance) do not change in the course of time ( t ) .

The "cake" filtration luw. This model assumes that particles larger than the pores of the medium are retained at the surface of the filter:

TP=at+ b (7) (ii)
Filtration in which membrane properties change during the microfiltration run.

(1)Particles of size around or larger than the pore size of the porous medium. The "complete blocking" filtration law. This model assumes that each particle which reaches the membrane participates in the blocking phenomenon by pore sealing. This leads to the assumption that particles are not superimposed:

l/TP=ct+d 03)
The "intermediate block& filtration law. It is assumed that particles settle on each other. The model evaluates the probability for a particle to block a pore: ln(TP) =et+f ( 9)

(2) Particles smaller than the pores of the membrane.

The "standard blocking" filtration law. This model assumes that pore volume decreases proportionally to filtered volume by gradual particle retention and build-up on the pore walls with possible plugging of the pores:

(l/TP)"=gt+h (10)

Analyses of foulants

After membrane rinsing at the conclusion of the MF trial, 3 cm long samples representing the inlet, middle and outlet parts were cut from the 1.20 m long tube. Fouling layers were analysed by two techniques: XPS, which characterizes the surface of the filtering medium, and IR spectrometry; which characterizes the total membrane, surface and bulk.

XPS spectroscopy. XPS measurements were made with an HA 100 hemisphere analyser (VSW, Manchester, UK) placed in an ultrahigh vacuum bell ( 1O-g-1O-'o Torr ). The surface under study was exposed to unmonochromatixed X-rays from a twin Mg/Al source (1253.6 eV Mg-Ka! and/or 1486.6 eV Al-Ka).

The photoelectrons produced are characteristic of the surface; the maximum depth of the analysis is 8-10 nm. Moreover, the appearance of electronif_ structures of carbon (Cls) and nitrogen (Nh) was typical of organic fouling. From the area of the peaks that represent each structure profile, the atomic composition could be calculated. The weak cross-section for photoionization of P2p explained the difficulty of observing the variations in phosphorus concentration. The calcium signal Ca2p3j2 appeared at a binding energy very close to that of Zr3p312.

The granular form of the Carbosep membrane surfaces prevented direct quantification of the signal intensities of fouling overlayers from electronic emission angle variations. However, in normal incidence, the intensity variation of the zirconium signal (Zr 3d ) could be measured, and its disappearance indicated a thickness greater than 8-10 nm. A study with an atomic force microscope (AFM, Centre ESCA Universite Claude Bernard, Lyon, France) for partly and severely fouled membrane samples confirmed the difficulty in quantifying the fouling thickness (very granular at the beginning and a flattened surface after heavy fouling, modifying the membrane's topography ) .

IR spectrometry IR results were computed as mass% of fouled membrane on mean samples that were removed from the active filtering layer which coated the carbon support with a fine spatula, as described by LabU et al. [ 61. The samples comprised the membrane's surface and the internal pore structure of the membrane. The results were referred to as "total fouling". The membranes used in the present experiment are somewhat more complex than the pure tetragonal ZrOz found in Carbosep UF membranes [6]. In addition to ZrOz, they contain titanium oxides that render them a grey colour (greater slope of absorbance vs. wavenumber for blank). The ZrOz structure is monoclinic. A new evaluation of the computing program was performed by the standard addition technique, giving a new value: czroz /eP = 140.

Results

M~rofdtration wrth dynamic counter pressure

Evolution of fouling versus time

Normalixed overall fouling hydraulic resistances (R&Z,) versus time for the four tests performed with the same operating conditions and stopped at various operating times (60,130, 250 and 320 min) are reported in Fig. 1. The R, of the membranes ranged from 1.0~ 1012 to 1.3 x 1012 m-l.

The shapes of the curves were quite similar and could be divided into two parts: the first corresponded to a slow increase in RJR, with time; during this period TP slowly increased in the range 0.3-0.6 bar, depending on the counter pressure mode and on membrane resistance. The second part showed a much quicker increase of RJR, while the stationary VCR was already achieved TP increased from around 1.0 bar to more than 3.0 bar in less than 100 min. Modelling of RJR, for the longest run according to eqns. ( 7)-( 10) exhibited a short initial period of filtration (up to 100 min) during which all models fitted the experimental curves.

After 100 min, both the "intermediate blocking" and "cake" filtration laws no longer applied; neither did the "standard blocking" filtration law after 190 min of filtration. The "complete blocking" filtration law was the only model that fitted the curves from the beginning to the end of the MF runs.

The contribution of reversible and irreversible fouling to the total fouling in the course of time is shown in Fig. 2. Durmg the shorter times of operation, reversible fouling Rfi contributed more than irreversible fouling Rfi to the evolution of Rf (60% as compared with 40% ). After 250 min of filtration RJR, still increased slowly, whereas reversible fouling increased rapidly and became the main contributor to total fouhng: RJR,= 85% of RJR, at the end of the experiment (310 min).

Ana.lyses of foulants

At the membrane surface (Fig. 3), the disappearance of the Zr signal indicated heavy fouling on the MF membrane (thickness > & 10 nm). The calcium and phosphorus concentrations varied more than proteins (N), indicating the contribution of calcium phosphate clusters to the whey fouling on the surface. This contribution increased as the fouling increased more quickly, since the ratio of protein to phosphate [calculated from N and Ca mass, assuming a Ca, (PO,), type of phosphate] decreased from about 15 at shorter times down to 3-4 at the end of the MF run. The AFM study confirmed that the fouling covered nearly all the surface (Fig. 4). The higher the fouling, the lower the roughness. The convolution between tip shape and pore shape influenced the apparent pore structures during the profile measurements, increasing the flattened appearance ]351.

In the total fouling, as seen by IR spectrometry (Fig. 3), the variation of proteins and phosphates in the course of time did not exactly correspond to the slow increase of irreversible fouling obtained from RJ& values, particularly during the last hour of MF, showing their contribution to a great increase of reversible fouling. The mixed material, proteins plus phosphates, exhibited a limited variation of the overall composition expressed as the ratio Prot/ PO1, its mean value being in the region of 50 before 250 min as compared to 30 at the end of MF. In all samples, the phosphates were identified as calcium phosphates (Fig. 5, sample 6). Their structure (Fig. 5) changed in the course of time, as expected for such slowly crystallixing phases. A broad maximum at 1075 cm-', linked to an amorphous calcium phosphate [ 361, progressively shifted to 1040 cm-', showing an apatite phase at the beginning of the crystallization process. This phenomenon was less marked at 320 min, when the withdrawal of retentate for ensuringa stationary VCR value of 5 increased the feed flow rate. In the feed and in the retentate, after a few hours' ageing, the aggregates underwent crystallixation as apatite, whereas the aqueous phase precipitated as an amorphous calcium phosphate-proteins mixed material. Consequently the intermedi-ate crystalhnity of the apatite observed in the fouling originated from aggregates built up during whey pretreatment and from the remaining ionic calcium and phosphates in the pretreated whey.

Heterogeneity

The distribution of both phosphates and proteins along the tube was far from regular (Fig. 6). The progressive transfer of fouling from the outlet to the inlet of the tube preceded a more pronounced increase of fouling from 250 min. After 320 min, phosphates and proteins reached the same level throughout the tube, with a constant Prot/P04 ratio of 30.

G G&an et al/J Membrane SCL 80 (1993) 131-145

MF selectivity

The OD of the permeate at the end of the longer experiment was 0.02, which indicated efficient clarification [ 371, compared with the initial whey OD of 0.64 (Table 1) .

Even though clarification was efficient, transmission of aggregates, as calculated from calcium concentrations, was estimated at 5% throughout the experiment. The transmission of calcium, which took into account ionic and precipitated calcium originating from calcium phosphate aggregation (produced during whey pretreatment), decreased during the first 200 min from 40% down to a plateau at 20% (Fig. 7).

Fliz 4 Atomic force microscope image of the surface of an Ml4 membrane fouled mth pretreated whey (a) after 60 mm of foul bng m dynamx counter pressure mode operation (DCPM), (b) after 320 mm of fouhng m DCPM During the slow increase of fouling (up to 130 min), the protein transmission decreased from 70 to ca. 60% (Fig. 7). After about 210 min of filtration, when more rapid increase of reversible fouling occurred, transmission of proteins to the permeate compartment decreased sharply down to 30% (Fig. 7).

Comparison between static @CPM) and dynamic (DCPM) counter pressure mode

Despite the difference between SCPM and DCPM, the curves of the overall hydraulic resistance (R&J vs. time were quite similar (Fig. 1) . Nevertheless, crossflow microfiltration performed using DCPM resulted in slower irreversible (RJR,) and reversible (RJR, )

fouling compared with SCPM (Fig. 2). As a consequence, operating time before severe foul-ing occurred was longer. For instance, the time to reach an RJR, value of 7.5 was 50% longer than that in SCPM (Fig. 1) .

At the end of the filtration in either mode, Zr became totally masked (Fig. 3) owing to a fouling layer thicker than 6-10 nm. The homogeneity along the tube and the nature of the surface irreversible layer were similar in both modes of operation, and the number of atoms measured was higher in SCPM compared to DCPM. Given that the thickness of the irreversible fouling layer revealed by the XPS analyses was constant for the different experiments, and that TP was lower at the end of the experiment performed in DCPM (compared with SCPM), it is likely that the irreversible fouling layer was less compressed.

No difference was detected in the total fouling: the same mean values for proteins and phosphates, the same Prot/PO, ratio (Fig. 3) and similar calcium phosphate structures (nearly amorphous) (Fig. 5) were observed. Nevertheless, the fouling distribution along the tube at the end of the MF run was quite different (Fig. 6): no variation was observed with DCPM, whereas with SCPM a regular decrease of fouling existed from the inlet to the outlet and was greater for phosphates than for proteins. Protein transmission was 5% lower with SCPM, a trend that was shown to be amplified at higher permeation fluxes [38]. As a consequence of lower fouling with DCPM, the recovery of protein when h/R, reached 7.5 was 67%, compared to 58% with SCPM. 4. Discussion

MF performance; TP heterogeneity

Besides the good efficiency of clarification, it is noteworthy that protein transmission was insufficient: around 30% at the end of the MF experiments. The figures were of the same or-der of magnitude as those found for an industrial plant [ 161.

Even though protein transmission was not improved much with DCPM, the enhancement of operating time could be explained by a lower overall fouling, which could be related to a more even TP distribution from the inlet to the outlet of the membrane tube. A striking difference between SCPM and DCPM was the distribution of fouling along the tube. With both modes of operation, a TP gradient (TP,-TP,) appeared, which was higher in SCPM

(TP,-TP,= +0.6 bar) than in DCPM (negative TP gradient; TP, -TP, = -0.2 bar). As a result, fouling was more evenly distributed with DCPM as compared to SCPM. At shorter times of operation using DCPM, fouling was higher in regions subject to a higher pressure difference. As a consequence, the less fouled areas under lower transmembrane pressure were forced to filter bigger volumes. Therefore they fouled more rapidly, so the fouling layer was evenly distributed by the end of the MF run. These results considered a movement of the effective filtering area on a macroscopic scale, which should be confirmed in a further study performed at SCPM under a higher pressure gradient.

It should be noted that Riesmeier et al.

[ 171 observed such a heterogeneity of local filtering conditions and fouling with crossflow MF of microbial cells. The authors called for more attention to be focussed on the module construction in order to lower the pressure drop in the retentate side. From our work it appears that DCPM is an adequate system for overcoming this obstacle.

Contrdmtwn of aggregates andproterns to foultng

The "complete blocking" filtration law was the only model that fitted the experimental data throughout the experiment. It exhibited the in-fluence of reduction of filtering area by particles, which revealed the role of aggregates. They accumulated at the membrane surface andpenetrated into pores, particularly during the last hour, when the reduction of filtering area led to a major increase of J per remaining active surface area (the experiments were performed at constant J). The aggregates formed during the pretreatment given to the whey were the principal source of calcium phosphates, which had a tendency to crystallize as apatite. Nevertheless, the remaining ionic calcium and phosphate might precipitate during the MF operation owing to the operating conditions: the same temperature as that of pretreatment (50°C); the pH of the feed (6.5) and of the retentate (6.4) after 190 min; the mean residence time in the feed tank and retentate compartment (280 min). Hickey and Hill [39] observed that UF pore blocking can occur more severely if apatite is permitted to form in the whey during a run rather than before it. This kind of inorganic foulant is known to cause a severe decline of membrane permeability in UF of raw whey ]7,401.

Nevertheless, according to spectroscopic analyses, proteins linked to aggregates and in a "free" state were the major foulant. "Free" proteins were dominant, since the ratio Prot/PO., exceeded 30 (Fig. 3)) which is much higher than in the aggregates, where the ratio was around 2 (proteins 54%, phosphates 28%, lipids 18% as determined by IR spectrometry). Their content was particularly high at the surface and in the bulk of the membrane relative to results found in the ultrafiltration of clarified whey, despite the lower specific membrane area of MF membranes (2 m2-g-' for M14) compared with UF (48 m2-ge1 for M5) [6,7].

"Free" proteins and aggregates participated m a reversible cake build-up and in the irreversible fouling. During microfiltering, the reduction of filtering area induced an enhanced transfer of proteins and aggregates towards the remaining filtering area. Then proteins were captured by a more concentrated and compressed cake under a higher TP and by the irreversibly fouled membrane. Such phenomena resulted in a decrease of protein concentration in the permeate compartment when Rd increased.

Selectivity

In the course of the MF operation, retention of proteins linked to calcium phosphate aggregates could not entirely explain the low total protein transmission. Therefore "free" protein transport through the filtering layer was altered by increased fouling.

According to Ferry's law [ 301 the clean Ml4 membrane with a mean pore diameter of 0.14 p and a hydraulic resistance of R, should readily transmit the main "free" whey proteins (Table 3). The calculated transmission of total proteins (linked and "free" proteins) was estimated to be 90%.

At shorter filtration times, the increase of hydraulic resistance due to irreversible fouling (R,+ R,) led to a reduction of the membrane pore radius (down to 0.043 p after 4 hr ) , which did not contribute significantly to the development of protein transmission: pores were still large enough to enable passage of protein through the membrane. The same conclusion was reached with the reduction of pore radius due to the irreversible fouling (R,+ R,) for longer operating times.

The overall fouling hydraulic resistance (R, + R,) was insufficient to account for a total protein transmission of 30%, even with its higher level at the end of the MF run (Table 3). Consequently, the large discrepancy between experimental and modelled Z'r values inclines one to reconsider the relevance of the assumptions made with respect to membrane fouling models: fouling is assumed to cause reduction of pore size when using Ferry's and Poiseuille's laws (eqn . (5)) [ 32 ] ) , while pores becoming blocked and sealed are supposed to account for the development of fouling in the MF experiments. Moreover, the heterogeneity of the system, which involves the development of fouling from the inlet to the outlet of the membrane, at the surface and in the bulk of the membrane as well as changes in pore size distribution with time [29,41], emphasizes the complexity of the fouling phenomena that have to be taken into account. The phenomenon of protein retention by MF membranes with pore sizes bigger than the proteins was reported [ 42-44]. It was explained for whey protein by the interaction of charged molecules with charges on the membrane [42] and for bovine serum albumin solution by the effect of shear on the protein molecules being sufficient to expose hydrophobic groups, which have a higher tendency to adsorb onto membranes and to induce aggregation of the more denatured form of protein [ 451.

According to the above, we suggest that more attention should be paid to the distribution of protein transmission along the membrane in the course of time, to the contribution of each imhvidual protein to the fouling and to protein retention during MF. For instance, the role of charge effects and protein-protein, proteinparticle, protein-membrane interactions, as well as membrane characteristics and pore microstructure, should be further investigated.

Conclusions

In pretreated whey MF, calcium phosphate aggregates and proteins were responsible for heterogeneous fouling that increased in the course of time according to a "complete blocking" filtration law accounting for a progressive decrease in the active filtering area, which moved along the membrane from the higher to the lower transmembrane pressure areas.

The dynamic counter pressure mode of operation provides a nearly constant transmembrane pressure gradient along the filtering module. Consequently, it is a precious scientific tool for investigating fouling phenomena. Moreover, it is an efficient means for improving the performance of MF systems, giving longer operating time and higher protein recovery.

The development of protein transmission in the course of time is not completely understood, and knowledge concerning the influence of microscopic heterogeneity (distribution of pore size, etc.) and of membrane-solute interactions need to be improved. a,b,c,d,e,f,g

List of symbols

[

  17,181. Operating at high flow velocity results in a high pressure drop along the filtering tube, which consequently produces different fluxes along the tube with time [ 191. A development patented by Alfa-Lava1 to overcome the high TP gradient along tubular modules consists in achieving a uniform TP difference throughout the whole length [ 20-221.

  [ 141: whey at 2' C, plus CaCl, up to a Ca concentration of 1.2 g-l-' and 10 M NaOH to adjust the pH to 7.2, was heated to 50°C in 30 min, with a holdmg time of 15 min. The aggregates were separated by MF.

  [ 301)) was suggested byMunch et al. [ 311, i.e.: All types of fouling generate a reduction of the hydraulic permeability of the membrane, which can be attributed to a reduction of the average pore radius [ 32 ] determined by the following relationship: r. is the pore radius of the clean membrane; R, is the membrane hydraulic resistance and R is the fouling hydraulic resistance. From eqn. (5) the reduction of transmission can be evaluated.The Stokes hydrodynamic radius (rm) of proteins was calculated from Loret et al.[33] using the following equation:

Fig 1

 1 Fig 1 Diagram of normahzed overall fouhng hydrauhc reslstance (RJR,) vs tnne for four expernnente performed m static (-) and dynannc (-) counter pressure mode operatlon(u=6Om-set-',P,=40bar,T=50°C,J=641hr-'-m-2)

Frg 2

 2 Contnbutlon of reversible (I&) and rrreverslble (R,) foulmg hydra&c resistances to the development of the overall fouling hydraulic res&ance (IL& referred to membrane res&ance (R,) vs tune (u=6 0 m-set-', Pr=4 0 bar, T=50"C!, J=64 1-hr-1-m--2, dynamic counter pressure mode operation, DCPM; statrc counter pressure mode, SCPM)

Fig 3

 3 Fig 3 Bar chart of component amounts and normahsed ureversrble foulmg hydrauhc resrstance (R&2,) vs time (u=6 Om-see-', Pr=4 Obar; T=50"C, J=641-hr-1-m-2, dynamic counter pressure mode operation, DCPM, static counter pressure mode SCPM)

  Fig 5 Absorbauce vs. wavenumber for comparable amounts of fouled Ml4 membrane (155 f. 10 B) taken m the middle of the tube (u=6 0 m-see-1, P,=4 0 bar, T=50"C, J=64 l-hr-1-m-2) Curve 1,60 mm MF at dynanuc counter pressure (amorphous profile), curve 2, 130 mm, curve 3,250 mm, curve 4,320 mm Curve 5,290 mm MF at statrc counter pressure Curve 6, sample 3 heated at 600" C (recrystalhzed apatite profile)

  Fig 7 Dragram of protein and calcmm transnussron (Z'r) into the permeate compartment vs tune (u = 6 0 m-set-', P,=4 0 bar, T=50"C, 5~64 l-hr-1-m-2, dynamlccounter pressure mode operatron)

  ,h constants of eqns. (7)-(10) C CF protein concentration (g-l-') concentration factor of aggregated calcium permeate concentration (g-l-' ) retentate concentration (g-l-' ) permeation flux (m3-m-2-sec-1 or l-hr-1-m-2) equivalent length of the membrane pore (m) molar mass (g-mol-' or Da) optical density mean retentate pressure (Pa or bar) pore radius (m or nm) molecular radius (m or nm) pore radius of the clean membrane (m or nm) fouling hydraulic resistance (m-l) overall fouling hydraulic resistance (m-l) irreversible fouling hydraulic resistance (m -' ) membrane hydraulic resistance (m-l) reversible fouling hydraulic resistance (m-l) time (set or min) transmembrane pressure (Pa or bar) transmembrane pressure at the inlet and at the outlet of the filtering tube (Pa or bar) transmission ( % ) transmission of aggregated calcium (%) protein transmission determined experimentally ( % ) transmission of "free" proteins not linked to calcium phosphate aggregates (%) , Functional propertres of protems m foods A survey, CRC Cnt Rev Food Scl Nutr , 4 (1976) 219 K.R. Marshall and W J Harper, Whey protein concentrates, Int Dairy Fed Bull ,233 (1988) 21 C V Morr and E.A Foegeding, Composrtron and functronahty of commercml whey and milk protein concentrates and isolates a status report, Food Tech-no1 ,43 (1990) 100 S H Richer%, C V Morr and C M Cooney, Effect of heat and other factors upon foammg properties of whey protein concentrates, J Food Sci ,39 (1974) 42 R J Pearce, S C Marshall and J A Dunkerley, Reduction of lipids m whey protein concentrates by mlcrofiltration, Int Dairy Fed Special Issue, 9201 (1992) 118 J.-P Labb& A Quhmerars, F Michel and G Daufin, Fouling of morgamc membranes durmg whey ultrafiltration analytical methodology, J Membrane SIX ,51 (1990) 293 G Daufin, J -P Labb4, A. Qu4merars and F Mrchel, Foulmg of an morgamc membrane durmg ultrafiltration of defatted whey protem concentrates, Neth Milk DanyJ,45 (1991)259 D N Lee and R L Merson, Chemical treatment of cottage cheese whey to reduce foulmg of ultrafiltrabon membranes, J Food Scl ,41 (1976) 778 U Merm and M Cheryan, Factors affecting the mechamsm of flux declme dunng UF of cottage cheese whey, J Food Process Preserv ,4 (1980, J E M Johns and M T O'Connell, The effect of the replacement of calcmm wrth sodmm on the ultrafiltratron of acid whey, N Z J Dairy Sci Technol ,16 (1981) 69 K P Kuo and M Cheryan, Ultrafiltratron of acid whey m a sprral-wound unit effect of operatmg parameters on membrane foulmg, J Food Sci ,48 (1983) 1113 J Patoka and P Jelen, Calcmm chelation and other pre-treatments for flux improvement in ultrafiltration of cottage cheese whey, J Food Scr , 52 (1987) 1241 C Tadd&, MCamsmes mfluencant le transfert de mat&e lors de l'ultrafiltration de lactodrum, Thesis, Toulouse Urnversrty, 1986 J Fauquant, S Vreco, G Brulk and J -L Maubols, Clarification des lacto&ums doux par agrdgatron thermocalcrque de la mat&e grasse r&rduelle, Lalt, 65 (1985) 1 J -L Maubois, A Pierre, J Fauquant and M Plot, Industrial fractionation of mam whey proterns, Int Dairy Fed Bull, 212 (1987) 154 G G&an, U Merm, G Daufin and J -J Maugas, Performance of an industrial mrcrofiltration plant for clanfymg rennet whey, Neth Milk Dairy J , submitted (1992). B Rlesmeier, K H Kroner and M -R Kula, Studies on secondary layer formatron and its characterization durmg cross-flow filtration of mlcrobral cells, J Membrane Sci ,34 (1987) 245 M Plot, J C Vachot, M Veaux, J -L Maubols and G E Brmkman, Ecr&nage et $uratron bact4nenne du Ian entier cru par mrcrofiltration sur membrane en flux tangentrel, Tech Lait Market, 1016 (1987) 42 U Merm and G Daufin, Crossflow microfiltration m the dairy industry state-of-the-art, La& 70 (1990) 281 R M Sandblom (Alfa-Laval), Filtermg Process, Swedish Patent No 7,416,257 (1974) M Mahnberg and S Holm, Low bacteria sknn milk by microfiltratron, North Eur Food Dairy J , 54 (1988) 75 E Plett, The constant pressure drfference method for microfiltration, m H G Kessler and D B Lund (Eds ) , Fouling and Cleanmg m Food Processmg, 1989, p 283 G Daufm, J -F Radenac, G G&an, F -L KerhervB, F Mrchel, U Merm and 0 Le Berre, A novel ng for ultra-and mrcrofdtratron for separatmg milk and whey components, Sep Scr Technol , submitted ( 1992 ) G Brule, J -L Maubols and J Fauquant, Etude de la teneur en 614ments mm&aux des produ&s obtenus lors de l'ultrafiltratlon du lalt sur membrane, Lart, 54 (1974exp4nmentale de la formation de la couche de polar-Isat1on, %me Con& FrancaB de an1e des Pro&&, Comp&me, Lavoisier, Vol 5,1991, p 73 AFNOR-ITSV, Contr5le de la quaht4 des prodmts la1tiers Recue11 des normes francaalses, S Amangllo (Ed ), 3rd edn ,1986 A Jaubert and P Martin, Reverse-phase HPLC analysls of goat casems Identification of a.1 and LYE genetic vanants, Lalt, 72 (1992) 235 J Folch, M Lees and G A Sloane-Stanley, A simple method for isolation and punficatlon of total 11p1ds from animal tissues, J B101 Chem ,266 (1957) 497 P Ammo, M Me&es and V Sanchez, A contnbutlon to the translation of retention curves mto pore size dlstrlbutlons for s1evmg membranes, J Membrane Sc1,54 (1990) 321 J D Ferry, Ultrafilter membranes and ultrafiltration, Chem Res ,18 (1936) 376 W D Munch, L P Zestar and J L Anderson, ReJection of polyelectrolytes from microporous membranes, J Membrane Sc1,5 (1979) 77 L Zeman, Adsorption effects 1n retention of macromolecules by ultrafiltration membranes, J Membrane Sc1,15 (1983) 213 C Lore&B Chaufer,B Sebllle,M Hanselm,Y Bla1n and A Le Hlr, Charactenzat1on and hydrodynamic behavlour of modified gelatin II Charactenzatlon by high performance size exclusion chromatographycomparison with dextrans and proteins, Int J B101 Macromol , 10 (1988) 366 H P Grace, Structure and performance of filter media, AIChE J ,2 (1956) 307 P Dletz, P K Hansma, 0 Inacker, H -D Lehmann and K -H Herrmann, Surface pore structures of mlcro-and ultrafiltration membranes imaged with the atomic force microscope, J Membrane Sc1,65 (1992) J -P Labbd, F Mlchel, G Daufin and F Bfioudet, Momllablllti et lnteractlons sohde-11q-u1de dans l'encrassement de divers matinaux par du lactos4um et du lalt, Lalt, 67 (1987) 465 A Pierre, Y Le Graet, J Fauquant, C Duner and A Kobllmsk1, Evaluation du rGle des param&res phys-1co-chmuques dans la clanficat1on du la&o&rum, Lalt, 72 (1992) 405 G G&an, G Daufm, U Merm, F Mlchel, F -L Ker-her& and J -F Radenac, Colmatage d'une membrane lnorgamque de mlcrofiltratlon par du lactos&um, 1n G Antonin and R Ben A1m (Eds ), B&me Cones Franca1s de GBn1e des Pro&d&, ComplBgne, Lavoisier, Vol 5,1991, p 19 M W H1ckey and R D Hill, Investlgat1ons mto the ultrafiltration and reverse osmosis of wheys II The effects of some minor whey constituents, N Z J Dauy Sc1 Technol ,15 (1980) 123 C Tadd&, G Daufm, P Almar and V Sanchez, Role of some whey components on mass transfer m ultrafiltration, Blotechnol B1oeng ,34 (1989) 171 J Hubble, Modelllng of protem rejection by mlcrofiltratlon membranes, 1n H G Kessler and D B Lund (Eds ) , Fouling and Cleanmg m Food Processmg, 1989, p 239 P Hememan, J A Howell and R A Bryan, Mlcrofiltration of protein solutions effects of fouling on rejectlon, Desalmatlon, 68 (1988) 243 V Gekas and B Hallstrom, Mlcrofiltratlon membranes, cross-flow transport mechamsms and fouling studies, Desalmatlon, 77 (1990) 195 H C Van Der Horst, Mlcrofiltratlon 1n whey processing, 1n J Charpin and L Cot (Eds ), First Int Conf Inorganic Membranes, Montpelller, 3-6 June 1989, p 297 ACM Franken, J T M Sluys, V Chen, A G Fane and C J D Fell, Role of protein conformation on membrane charactenstlcs, 5th World Filtration Congr , Nice, 5-8 June 1990, Soc1Qe FranFalse de F11tratlon, Cachan, Vol 1, p 207

TABLE 1 Compoaltlon of the feed whey, pretreated whey, superna- tant and sediment of centrifuged pretreated whey (2000 g,

 1

Acknowledgements

This work was supported by a grant from the Etablissement Public FGgional Bretagne (Contract No. 3051 B). The authors gratefully acknowledge the valuable contribution of F.-L. Kerhervh and J.-F. Badenac in building the counter pressure system.