Dr Anthony Fardet
email: anthony.fardet@clermont.inra.fr

Didier Dupont

Laurie-Eve Rioux

Sylvie L Turgeon

Influence of food structure on dairy protein, lipid and calcium bioavailability: A 1 narrative review of evidence 2 3 4

Keywords: Dairy products, food structure, protein, lipid, calcium, bio-accessibility, bioavailability 52

come

 195Subsequently, the study of [START_REF] Tunick | Effect of heat and homogenization on in vitro digestion of milk[END_REF] investigated the role of milk 196 processing treatments on proteins and lipids digestion. Raw skim milk, raw whole milk, 197 homogenized raw whole milk, pasteurized whole milk, homogenized HTST-pasteurized whole 198 milk, homogenized UHT-sterilized whole milk, HTST-pasteurized skim milk and UHT-sterilized 199 skim milk [START_REF] Tunick | Effect of heat and homogenization on in vitro digestion of milk[END_REF] were prepared. Before digestion, the protein profiles of most milks

301

Similar results were obtained by the same research team in 2012 [START_REF] Lamothe | Influence of cheese matrix on 1566 lipid digestion in a simulated gastro-intestinal environment[END_REF].

302

Mild Cheddar (31% lipid), aged Cheddar (34% lipid), light Cheddar (23% lipid) and Mozzarella 303 (25% lipid) cheeses were also submitted to in vitro gastro-intestinal digestion and investigated for 304 the association between texture and disintegration rate and extent. After two hours of gastric 305 digestion aged Cheddar was clearly the more rapidly disintegrated compared to other three cheeses 306 (≈ 65 versus ≈ 20-30%); but differences were again leveled after two hours duodenal digestion even 307 if kinetics differed. In all cheeses tested, the most important changes in matrix disintegration were 308 observed within the first 30 min of the duodenal phase. Finally the fat content also affected 309 degradation in the duodenal phase. (hard cheese, ripened for 90 days) [START_REF] Qureshi | Angiotensin I-converting 1620 enzyme-inhibitory activity of the Norwegian autochthonous cheeses Gamalost and Norvegia 1621 after in vitro human gastrointestinal digestion[END_REF]. The Gamalost is prepared by boiling milk 313 of lean cow without adding rennet, contrary to what is customary in Europe. The Norvegia cheese is 314 a trademark of cheese with secret recipe and close to Gouda. It melts easily with heat. The two 315 cheeses therefore have different matrices. Overall Gamalost cheese gave more peptides after 316 digestion than for Norvegia cheese, most of them derived from β-casein, some of casein α s1 and 317 only a few from casein α s2 and κ. After digestion, both cheeses led to increase amounts of released 318 aromatic and positively charged amino acids, and leucine; but considering all amino acids, 319 Gamalost cheese released higher quantities than Norvegia cheese. Some peptides remain intact after 320 digestion and more peptides were generated after gastric than duodenal digestion. Such results again 321 emphasized an important matrix effect for cheeses with different initial texture.

322

In the end, cheeses were more resistant to protein and lipid digestion than liquid or semi-323 solid matrices were. No direct relationship could be established between disintegration kinetics and 324 cheese rheological properties [START_REF] Lamothe | Influence of dairy matrices on 1568 nutrient release in a simulated gastrointestinal environment[END_REF]. The matrix effect was first tested in minipigs consuming yogurt or milk (Gaudichon et al., 328 1994).This study was of great interest because it was a sensu stricto bioavailability study using a 329 radiolabeled yogurt and milk with nitrogen 15 N allowing differentiation between endogenous and 330 exogenous nitrogen. First, there was no effect of both dairy matrices on nitrogen endogenous minutes of digestion the rennet gel led to lower levels of duodenal proteins and plasmatic amino 368 acids. In addition the rennet gel appeared more statietogenic (plasma CCK). Authors proposed the 369 following explanation for the observed effects, i.e., a combined action of three mechanisms: 1) a 370 strong resistance of the rennet gel to hydrolysis in the stomach, 2) combined with a longer gastric 371 retention time, and 3) a substantial dilution by gastric juices; besides, while acid gel flocculated in 372 stomach without apparent syneresis the rennet gel exhibited an extensive syneresis indicating a 373 strong contraction of gel particles leading to a more pronounced retention and a delayed gastric 374 emptying. In addition particle contraction has limited enzyme accessibility to cleavage sites of 375 proteins [START_REF] Kong | Disintegration of Solid Foods in Human Stomach[END_REF]. Therefore, the time of gastric residence might induce satiety with 376 potential application in developing diets for loosing weight in case of obesity (Kong and Singh,377 2008). On the contrary, the impacted bioavailability of amino acids may have a potential effect on 378 splanchnic and peripheric protein metabolism with potential application in elderly populations for 379 which the preference for acidified milk would induce a more efficient muscular synthesis.

380

In their third study Barbé et al. went further through identification (by LC-MS/MS) of 381 released peptides in the gastrointestinal tract of minipigs from six distinct dairy matrices with 382 similar composition but with different physical structure (Barbé et al., 2014a). Duodenal effluents 383 were collected upon five hours after consumption of the six following dairy matrices (which were 384 prepared from Ultra Low Heat (ULH) skim milk powder): 1) heated milk (90°C for 10 minutes), 2) 385 raw milk, 3-4) corresponding rennet gels, 5) acid gel from heated milk, and 6) stirred acid gel from 386 heated milk. Authors reported that 16 000 peptides were clearly sequenced and identified and the 387 dairy structure had only a little influence on the localization of cleavage sites as regards with protein 388 sequences. However structure strongly impacted the number of identified peptides more specifically 389 for rennet gel that led to three-fold less identified peptides. As for the previous study effect was 390 attributed to the the more important degree of dilution in the stomach by digestive secretions plus a 391 longer gastric retention. These results led to an important conclusion: more than proteolysis 392 mechanisms the dairy matrix structure strongly impact dairy protein digestion kinetics. All collected human studies were led in healthy adults; but only one study stricto sensu studied the 425 effect of dairy matrices -as eaten -on protein metabolism in humans [START_REF] Gaudichon | Exogenous and endogenous nitrogen flow-rates and 1493 level of protein hydrolysis in the human jejunum after N-15 milk and N-15 yogurt ingestion[END_REF].

426

Other studies used casein or whey fractions (Boutrou et al., 2013;Churchward-Venne et al., 2015; 427 [START_REF] Gaudichon | Net postprandial utilization of N-15 -labeled 1490 milk protein nitrogen is influenced by diet composition in humans[END_REF], or compared cottage cheese with eggs (Nuttall and Gannon, 1990).

428

The bioavailability study by Gaudichon et al. pointed out to the role of dairy matrices on 429 protein digestibility in sixteen healthy adults (average age of 30 years) by using radiolabelled milk 430 and yogurt (from the same milk) with 15 N [START_REF] Gaudichon | Exogenous and endogenous nitrogen flow-rates and 1493 level of protein hydrolysis in the human jejunum after N-15 milk and N-15 yogurt ingestion[END_REF]. Both products significantly 431 stimulated endogenous nitrogen secretion 20-60 minutes after consumption, and upon four hours 432 endogenous nitrogen flow rate did not differ between both matrices. An expected high level of 433 proteolysis was also observed for both matrices. However the yogurt led to delayed gastric 434 emptying as regards with exogenous nitrogen flow rate as compared to milk. Otherwise when 435 evaluating the net gastro-jejunal exogenous nitrogen absorption there was not significant difference 436 between milk (57%) and yogurt (51%). Finally, concerning non-protein nitrogen, the measured flow 14 rate for yogurt tended to be higher to that of milk between 40-100 minutes after consumption. As 438 shown with mini-pigs it seems that the stomach step plays an important role in controlling the 439 delivering of protein in the small intestine and for the further absorption of amino acids with 440 potential application for protein anabolism especially in elderly populations.

441

The study by Boutrou et al. does not relate to complex dairy matrices as usually consumed 442 but casein and whey proteins (Boutrou et al., 2013). However, since these two milk proteins have 443 different structures, the results obtained give interesting information on the peptide profiles and the 444 presence of bioactive peptides after digestion at the jejunal level according to these two protein 445 structures. The study has been led during 6 hours post-prandially in thirteen healthy adults (18-40 446 years old) consuming 30 g of either radiolabelled ( 15 N) casein or lactoserum. First, the recovery of 447 dietary nitrogen indicated that 50% and 60% of ingested nitrogen had already been absorbed after 6 448 hours at the jejunal level in WP and casein groups, respectively. Then the jejunal peak of exogenous 449 nitrogen after whey consumption was largely higher than that of casein at 0.5-1 hour after 450 consumption; but casein showed a more regular and lower nitrogen profile in agreement with 451 previous results about rapid versus slow protein (Boirie et al., 1997). And the peak of jejunal 452 peptides was around 0.5-2.5 hours for casein and one hour for whey. Casein was a more important 453 peptide precursor at jejunal level with 356 identified and sequenced peptides against 146 for whey.

454

Casein peptides also presented varied biological activities and were of average size, i.e., 750-1050 455 KDa during 6 hours while whey presented during 3 hours peptides with larger size, i.e., 1050-1800 456 KDa. Moreover, the quantities of casomorphins β (caseins β 57, 58, 59 and 60-66) and casein β 457 108-113 released were sufficient to obtain a biological action of these peptides (i.e., respectively 458 opioid and antihypertensive).

459

The second study by Gaudichon et al. did not compare different dairy matrices but it 460 deserves to dwell on it because it indirectly evaluates the "matrix effect" of milk by comparing the 461 protein digestion of radiolabeled casein alone and in the presence of sucrose or milk lipids 462 [START_REF] Gaudichon | Net postprandial utilization of N-15 -labeled 1490 milk protein nitrogen is influenced by diet composition in humans[END_REF]. Thus, 25 healthy male and female subjects (mean age of 29 years) 463 consumed three different diets, each containing 30 g of defatted milk proteins labeled with 15 N: 1) 464 milk protein alone; 2) milk proteins + sucrose (100 g); and 3) dairy protein + 43 g of dairy lipids 465 (from 36 g of butter and 46 g of cream). Sucrose clearly slowed down protein absorption on longer 466 time than lipids but in the end ileal digestion did not differ between the three diets (around 95%).

467

Sucrose also significantly reduced post-prandial transfer of nitrogen from milk to urea but not lipids 468 again. Secondly the net post-prandial milk protein utilization (8 hours after meals) was significantly 469 higher with sucrose (85%) compared to protein alone or with lipids (80%). According to authors 470 « This study shows that energy nutrients do not affect the nitrogen absorption but modify the 471 metabolic utilization of dietary protein in the phase of nitrogen gain » [START_REF] Gaudichon | Net postprandial utilization of N-15 -labeled 1490 milk protein nitrogen is influenced by diet composition in humans[END_REF]. In the following study, Churchward-Venne et al. have hypothesized that the digestion and ingestion of micellar casein is modulated by the dairy matrix (Churchward-Venne et al., 2015).

475

Their assumption or hypothesis was based on the well-known fact that the slow digestion and slow 476 kinetics of amino acid uptake from isolated micellar casein are believed to be responsible for the 477 relatively lower postprandial response of muscle protein synthesis compared to those obtained with 478 more rapidly digested proteins such as isolated whey. In this study subjects were older than in 479 previous one (average age of 71 years) and consumed 600 mL casein with 13 C leucine in either water or 50 g cottage cheese or egg white. After 8 hours the area under curve for plasma nitrogen 494 from amino acids and urea was lower by 50% for egg white compared to cottage cheese, notably 495 between 0-4 days. This was associated with a 50% lower protein conversion in urea. Overall 70% of 496 cottage cheese might explain the urea formation and only 47% for egg white. Finally cottage cheese 497 exhibited a better protein digestibility. First of all, it should be noted that there are, in the end, very few studies comparing the digestive 501 evolution, more particularly that of proteins, of dairy products as consumed by man and presenting 502 different matrices. From the synthesis of in vitro, animals and human studies, it is difficult to draw 503 firm conclusions about the influence of the dairy matrix on digestibility, bio-accessibility, 504 bioavailability and nutritional effects of the protein fraction. However, some conclusions, although 505 still partial, can be proposed in relation to the studies described above (see also In pigs, based on dairy matrices of the same composition but differing in their internal structures, 509 the large differences in the kinetics of absorption of amino acids can be fully understood by 510 considering behavior of dairy matrices in the stomach. Compared to gelling by rennet, acid gelling 511 results in a higher peak of duodenal proteins as well as for amino acids, suggesting resistance of 512 rennet gel to gastric digestion; but the differences are leveled at the jejunal level. More generally, 513 gelation slows gastric emptying and subsequent absorption of amino acids, and decreases their 514 bioavailability in peripheral blood. Moreover, the structure of dairy matrices strongly affects the 515 kinetics of digestion of proteins rather than the mechanisms of proteolysis per se. Another main 516 conclusion is that both microstructure and macrostructure are affected by heating and gelification 517 processes, respectively, and that both impact differently proteolysis steps, microstructure acting 518 more on hydrolysis and macrostructure more on amino acid absorption and bioavailability.

Milks versus yogurts versus fermented milks (in vitro, mini-pigs and humans) 544

The digestion of casein begins during the gastric phase and appears slower for pasteurized milk than 545 for yogurt. At the end of duodenal digestion, no intact casein is present in the different dairy 546 matrices, while small bands of whey proteins are still visible for pasteurized milk and yoghurt 547 compared to sterilized milk. The release of free amino acids during the duodenal phase varies 548 according to their nature (acid, basic, neutral or hydrophobic) and appears to be governed by the 549 specificity of the enzymes. For both types of matrix, the hydrophobic amino acids are released in 550 significantly greater amounts than other types of amino acids. But overall, total protein digestibility 551 seems to be identical between milk and yoghurt even though yogurt digestion results in different

559

In mini-pigs, milk and yogurt proteins are also highly digestible (93%); and the kinetics of 560 exogenous nitrogen delivery in the intestine is highly correlated with that of exogenous nitrogen 561 uptake for milk and yoghurt. Gastric emptying also appears to be a major factor for controlling the 562 kinetics of nitrogen absorption, the higher viscosity of yogurt allowing a more regular release of 563 nitrogen into intestine leading to a more gradual absorption and distribution of dietary nitrogenous 564 compounds within organism. Finally, in man fermentation only modifies the rate of gastric 565 emptying of nitrogen (delayed with yoghurt) and does not affect the level of hydrolysis of milk and 566 yoghurt made from the same milk, stimulation of endogenous nitrogen and digestibility rate.

567

Whether in the mini-pig or man stomach seems to play a very important role in controlling the 568 emptying of more or less hydrolyzed proteins in the small intestine. Initially the study by Kopf-Bolanz et al. was dedicated to validate an in vitro digestion 584 system for investigating macronutrient decomposition in human; and homogenized and pasteurized 585 milk was chosen as an example of a complex food matrix [START_REF] Kopf-Bolanz | 1559 Validation of an in vitro digestive system for studying macronutrient decomposition in humans[END_REF]. Although 586 there is no comparison between different dairy matrices, the results on digestion of the lipid fraction 587 deserve to be reported: first, the digestion process increased free fatty acid content from 1,04 to 62,8 588 mmol/L, i.e., 41% of total milk fat content (however, assuming that all triglycerides present in 589 whole milk were hydrolyzed into two free fatty acids and one monoacylglycerol, this value 590 corresponded to 100% of the triglycerides); second, as regards with fatty acid distribution, more 591 short-chain fatty acids (i.e., around 11%) were released after digestion compared to relative total 592 fatty acid content before digestion (i.e., around 6%).

593

Subsequently, in the study of [START_REF] Tunick | Effect of heat and homogenization on in vitro digestion of milk[END_REF], described above for protein 594 digestion, authors investigated the role of milk processing treatments on proteins and lipids 595 digestion. Homogenization increases free fatty acids release attributed to the increase surface area 596 improving lipase efficiency (Armand et al., 1992). This was confirmed by the confocal microscopy

671

Therefore, for cheeses, greater fatty acid release could not be related to faster matrix 672 disintegration, suggesting that the lipid droplet size dispersion was more important than matrix 673 breakdown was for the modulation of lipid digestion kinetics [START_REF] Lamothe | Influence of dairy matrices on 1568 nutrient release in a simulated gastrointestinal environment[END_REF]. Human studies comparing the effect on lipemia of different ready-to-eat usual dairy matrices are not 705 so numerous. In the ten selected studies milk, fermented milk, butter, cheese, cream and yogurt 706 have been tested against lipemia mainly in healthy adults, but also in subjects with metabolic 707 syndrome, type 2 diabetes, and mildly hypercholesterolemic.

708

In the first and recent randomized and crossover study the impact of the cheese matrix on 709 postprandial lipemia in healthy humans has been evaluated [START_REF] Drouin-Chartier | Differential impact 1437 of the cheese matrix on the postprandial lipid response: a randomized, crossover, controlled trial. 1438[END_REF]. Subjects 710 consummed 33 g fat from a firm cheese (young cheddar), a soft cream cheese (cream cheese), or 711 butter (control) incorporated into standardized meals that were matched for macronutrient content. (80 g/day) that contains 27% fat and 800 mg/100 g calcium; 3) control (n = 50). After intervention, 727 no increase in LDL and total cholesterol was observed in the 'cheese' groups compared to the 728 control. However, a stratified analysis showed that subjects in the Norvegia group with the 729 metabolic syndrome showed significant reductions in total cholesterol at the end of the intervention 730 compared to the control group (-0.70 mmol/L, p = 0.013) and also of triglycerides. In the Gamalost 731 group, subjects who had a high total cholesterol level at baseline showed a significant reduction in 732 total cholesterol compared to control (-0.40 mmol/L, p = 0.035).

733

In the next randomized 3 x 2 week crossover study semi-hard cheese was compared to 734 skimmed milk in 15 healthy young men [START_REF] Soerensen | Effect of 1667 dairy calcium from cheese and milk on fecal fat excretion, blood lipids, and appetite in young 1668 men[END_REF]. Focusing on the specific potential 735 effects of cheese calcium versus calcium in liquid milk, Soerensen et al. compared the effects of 736 consumption of three isocaloric diets with similar lipid content and composition and varying in 737 calcium intake. The calcium intakes in each of the three intervention periods were 400 mg/day 738 without dairy (control), or 1700 mg/day including 800 mg/day via dairy products, either as 670 739 mL/day of skimmed milk, or 120 g/day of semi-hard cheese. Compared to the control diet, each of 740 the two dairy-based diets limited total cholesterol and LDL cholesterol blood increases, but had no 741 effect on triglycerides and HDL-cholesterol (no difference between the two dairy products), and 742 resulted in a higher fecal lipid loss, which seems to be explained by their calcium content.

743

Therefore, although the effect on blood lipids do not differ substantially between milk and cheese 744 consumption with similar calcium contents, results of this study support that calcium-rich dairy 745 foods may be less atherogenic than their calcium-poor counterparts.

746

The following intervention study was performed in 159 moderately hypercholesterolemic 747 French patients (without treatment) consuming twice daily 30 g of Camembert or 250 g of whole 748 yogurt for 5 weeks [START_REF] Schlienger | Effect on blood lipids of 1650 two daily servings of Camembert cheese. An intervention trial in mildly hypercholesterolemic 1651 subjects[END_REF]. No significant difference for all lipid parameters was 749 observed both between groups and after the intervention, i.e., total cholesterol, HDL-and LDL-750 cholesterol and triglycerides. ). The cheese-based diet resulted in plasma LDL cholesterol concentrations 6.9% lower than 755 the butter-based diet. Given the composition of the diets, the authors ruled out that this may be due 756 to differences in calcium and protein concentrations between cheese and butter, and suggest 757 mechanisms related to fermentation and a "matrix effect" due to the dispersion of the fat globules in 758 the solid casein matrix of the cheese.

759

In another randomized cross-sectional study, healthy volunteers were subjected to a diet in 760 which 20% of their total energy intake was provided by dairy fat, either in the form of hard cheese, 761 milk or butter [START_REF] Tholstrup | Does 1670 Fat in Milk, Butter and Cheese Affect Blood Lipids and Cholesterol Differently?[END_REF]. On the fourth day of each 3-week intervention period, an 762 acute postprandial test was performed with the test product. These tests revealed no difference in 763 the amount or profile of chylomicron fatty acids from cheese, milk or butter. However, a long-term 764 effect was observed: daily cheese consumption resulted in lower total cholesterol and LDL-765 cholesterol than that of butter. These results are in agreement with the previous observation of a 766 lower total cholesterol level after consumption of cheese ('Jarlsberg', Swiss type) than butter 767 (Biong et al., 2004), both studies using diets where dairy fat constituted 20% of the energy intake.

768

At equal fat content the cheese can therefore be less hypercholesterolemic than butter (no 769 differences for triglycerides and HDL-cholesterol).

770

The last study with cheese has been led in diabetic subjects (Clemente et al., 2003). Test 771 meals containing 30 g of fat in the form of Mozzarella cheese or milk resulted in a peak plasma of 772 triglycerides earlier than the same amount of butterfat, although the cumulative absorption of 773 triglycerides on 6 hours (area under the curve) was similar in all groups. In addition, the rate of 774 gastric emptying is significantly faster with Mozzarella than with butter or milk. The authors 775 conclude that « while the physical structure of fat-rich foods has no major effect on postprandial 776 plasma triglyceride concentrations, it is able to influence the timing of triglyceride peak; gastric 777 emptying time does not play a major role in modulating the postprandial response of triglycerides 778 and glucose ».

779

In the last two studies fermented milk [START_REF] Sanggaard | 1641 Different effects of whole milk and a fermented milk with the same fat and lactose content on 1642 gastric emptying and postprandial lipaemia, but not on glycaemic response and appetite[END_REF] and yogurt (Rossouw et al., metabolism, rate of gastric emptying and appetite [START_REF] Sanggaard | 1641 Different effects of whole milk and a fermented milk with the same fat and lactose content on 1642 gastric emptying and postprandial lipaemia, but not on glycaemic response and appetite[END_REF]. Lactose was added to 784 the fermented milk to equalize the lactose contents of both products. Fermented milk results in a 785 significantly slower rate of gastric emptying (p <0.001), probably because of higher viscosity. In Overall, these works show that differently structured dairy products, including cheeses, can result in 815 different profiles of postprandial lipemia. First, fatty acid release in the intestinal phase was much 816 faster when matrices were produced from homogenized milk [START_REF] Lamothe | Influence of dairy matrices on 1568 nutrient release in a simulated gastrointestinal environment[END_REF]. Second, the 817 composition of the cheeses, their viscosity and the presence of a matrix that is more or less solid, as 818 for a pressed cooked cheese compared to a fresh cheese, could affect the kinetics of digestion of the 819 lipids of cheeses. Indeed, the higher the viscosity of the food bolus, the longer the gastric emptying 820 time, which results in delaying the peak of postprandial triglyceridemia. This raises the question of on the metabolism of fat, especially when consumed as such in the French way, and not primarily in 823 a melted form as in North America. On the basis of the in vitro and in vivo studies presented, "elastic" type) but the final rate of release does not differ after four hours of digestion. In the rat, lymphatic absorption of lipids is faster for cream and sour cream compared to a cream 843 cheese and butter. Viscosity, type of emulsion, particle size and protein content could play a role in 844 the degree of lipolysis with identical composition of fatty acids. In humans, postprandial or multi-845 week intervention studies were performed either in healthy subjects or at risk for chronic diseases.

846

Their results give indirect indications on "dairy matrices" effects according to the differences of 847 lipemiae observed: 848 1) Hard cheeses cause LDL-cholesterol levels -and probably total cholesterol -to be 849 significantly lower than butter; but this does not mean that the butter is 850 hypercholesterolemic; 851 2) A semi-hard cheese does not give a different cholesterolemia than a skim milk; were tested for the bioavailability of calcium in vitro (after dialysis): whole or skimmed milk, whole 871 or skimmed milk yogurt, fermented milks, and various cheeses (Turkish pickled white Cheese, 872 tulum cheese, cream cheese, kashari cheese and whey cheese) [START_REF] Unal | In vitro determination of calcium bioavailability of milk, 1678 dairy products and infant formulas[END_REF]. The products 873 differ in their acidity (percentage of lactic acid), ranging from 0.11% for whole milk to 1.78% for 874 Turkish pickled white cheese. The skimming of milk does not significantly alter the dialysability of 875 calcium, which is about 26-28%. For yogurts as well as for milks, no significant difference is 876 measured (28-33% bioavailability), leading the authors to conclude that the milk fat content has no 877 effect on bioavailability of calcium. On the other hand, significant differences are observed for 878 cheeses: from 14% for cream cheese to 32% for whey cheese. The study also shows that there is no 879 significant correlation between cheese acidity and calcium bioavailability. In accordance with the 880 literature (Allen, 1982), the authors attribute differences in bioavailability to the 881 phosphorus/calcium (P/Ca) ratio of cheeses, cream cheese having the highest ratio and whey cheese 882 the lowest. Finally, of all dairy products, skimmed milk yoghurt has the highest calcium 883 bioavailability (33%, p < 0.05). In another study the value obtained for cow's milk dialysability was 884 20%, a value lower than that calculated in the study by [START_REF] Unal | In vitro determination of calcium bioavailability of milk, 1678 dairy products and infant formulas[END_REF]. Shen et al.

885

also measured the dialysability of calcium from whole and skimmed cow's milk using in vitro 886 digestion [START_REF] Shen | Estimation of the bioavailability 1656 of zinc and calcium from human, cows, goat, and sheep milk by an in-vitro method[END_REF]. The values obtained are of the same order of magnitude as the 887 previous studies, namely 19.6% for whole milk and 23.2% for skimmed milk, the difference not UHT milk (Ngounou et al., 2003). The determination of the soluble calcium in the fermented milks 892 obtained shows, whatever the bacterial strain, an increase in the solubility of this mineral. The 893 association of the two strains, while maintaining a high level of solubilization of the minerals, 894 appears less effective than the strains in individual cultivation. For example, with a single strain, 895 solubilization of calcium can reach almost 80%, whereas with two associated strains, the maximum 896 does not exceed 70%. The authors give no explanation for these differences and conclude that the 897 efficacy of these wild strains in solubilizing calcium justifies the interest of their biochemical In the five following studies several distinct dairy products were compared in rats for their calcium 928 bioavailability.

929

In the first study, the objective was to compare the biological availability (measured by 930 apparent absorption and bone mineralization) of calcium in rats fed diets based on milk and various 931 dairy products (semi-hard/hard cheese L'Envol made from skimmed milk with 4% fat, skimmed 932 milk yoghurt and skimmed milk powder) containing various proportions of dairy proteins and 933 calcium chemical forms [START_REF] Delisle | Biological availability of calcium and magnesium from 1431 dairy products[END_REF]. The apparent absorption of calcium from cheese was 934 higher (≈35%) than from skimmed milk, yoghurt and skimmed milk powder (≈13-18%) in young 935 rats (6 weeks) whereas in adult rats (16 weeks) the apparent absorption of calcium is lower from 936 cheese than from other dairy products. Nevertheless, the deposition of calcium at the level of the 937 tibia and the femur and bone resistance were the same for all the diets. hours at 4°C for the 3 products) with 47 Ca. First, the apparent absorption of 47 Ca is 69, 72 and 59%

943

for milk, yogurt and cheese, respectively; and the apparent retention of 47 Ca is 61, 64 and 54%, 944 respectively. In the tibia, there were no significant differences in retention (4.0-4.4%) and powder and calcium carbonate with or without 0.05% ascorbic acid were administered in rats 952 (Poneros and Erdman, 1988). Ascorbic acid has no influence on the bioavailability of calcium. The 953 cheese had a higher calcium bioavailability (105%) -but not significant -compared to skimmed 954 milk (95%). The calcium content of the tibia (calcium tibia/calcium ingested) was also not 955 significantly different. It is surprising to find such high values, in particular greater than 100%. 956 However, relative bioavailability was measured from the calcium tibia content according to the 957 formula: tibia calcium (mg)/total consumed calcium (g); with a value of 100% attributed to calcium 958 carbonate without ascorbic acid. Streptococcus thermophilus and Lactobacillus bulgaricus), 3) yoghurt termed acidophilus (cultured 963 with S. thermophilus and L. acidophilus) (Kaup et al., 1987). First, the ash bone content increased 964 with milk but not with yogurt; second, rats fed with milk with added lactic acid had thicker femurs 965 than with yogurts; thirdly, rats given yogurts and acidified milk had femurs with higher bending 966 moments (induced reaction when an external force or moment is applied to an element causing its 967 flexion) than rats given unacidified milk; finally bone strain decreased and the modulus of elasticity 968 increased as ingested calcium increased. Authors concluded that « the improved bone characteristics 969 in rats given milk, and particularly in those given acidified or cultured milk, in diets at constant 970 lactose content indicate that lactose is not the only contributor to the high bioavailability of calcium 971 in milk products and that lactic acid may also be a factor » (Kaup et al., 1987).

972

In the last study Dupuis et al. have studied the use of calcium from calcium carbonate 973 (lactose-free control group) and from three dairy matrices (skimmed milk, yogurt and processed 974 cheese) in growing (8 weeks) and ageing (14 months) rats [START_REF] Dupuis | Bioavailability of calcium in milk, yoghurt and 1443 processed cheese -Etude comparee de la biodisponibilite du calcium d'un lait, d'un yoghourt et 1444 d'un fromage fondu[END_REF]. First, the calcium 975 of milk products was better utilized than in the control. During ageing and lactation, the milk and 976 yoghurt diets had the lowest bone exchanges while being higher in the control diet in the absence of 977 Ca utilization factors. Authors suggested that lactose may be responsible for differences in bone 978 exchanges of calcium within the milk products used. In the four following studies calcium absorption and retention were measured in mice and rats. In 982 the first study carried out in mice, although not clearly explained, the milk used appears to be an 983 unprocessed whole cow's milk [START_REF] Singh | Heat 1659 stability and calcium bioavailability of calcium-fortified milk[END_REF]. The percentages of absorption and retention of 984 calcium are respectively 50 and 44%, values lower than those observed in the rat in the next studies.

985

Thus in the study by Toba et al. in 7-week-old rats the apparent uptake of calcium was 986 approximately 80% and only 45% in 12-week-old rats [START_REF] Toba | Effect of lactose and milk protein on bioavailability of 1673 calcium carbonate in growing rats (in Japanese)[END_REF]. The study by Brink et al.

987

was carried out in rats fed, inter alia, with a sterilized cow's milk in a diet supplemented with a 988 mixture with or without minerals and proteins in a first experiment, and with or without a mixture 989 of magnesium, sodium and potassium in a second experiment (Brink et al., 1992). In the first 990 experiment the absorption of calcium is 77% for normal milk and only 59% with the addition of a 991 mixture of minerals and proteins. In the second experiment, the absorption of calcium is similar and 992 is 74%, the addition of magnesium, sodium and potassium having only a small impact on this 993 absorption reduced to 70%. The last study compared the bioavailability of calcium in rats from 994 dried skim milk, white bread and wholemeal bread [START_REF] Ranhotra | Bread 1623 (white and whole wheat) and nonfat dry milk as sources of bioavailable calcium for rats[END_REF] (Perez-Conesa et al., 2007). It is also possible that short-chain fatty acids can 1016 directly stimulate calcium absorption in the rat colon and that at least calcium could pass through 1017 the cell membrane more readily in the form of a less charged complex (acetate-calcium) via a 1018 passive route [START_REF] Lutz | Effect of short-chain fatty acids on calcium absorption by the rat 1585 colon[END_REF]. [START_REF] Klobukowski | Calcium bioavailability from 1555 dairy products and its release from food by in vitro digestion[END_REF] recall in their review that the 1023 highest percentages of calcium apparent absorption and retention are observed for fresh cheese 1024 produced either by a conventional method (acid coagulation) (90.3% and 84.2%, respectively) or 1025 with the addition of probiotic Lactobacillus plantarum (90.5% and 86.3, respectively) 1026 (Kłobukowski et al., 1997b); this compared with the refined cheese (59.6-76.3% and 64.4-81.3%, 1027 respectively) produced by immersion in traditional (2% NaCl) or modified (NaCl and KCl solution 1028 at 1:1) brines or unrefined Ricotta-type cheese (57.4-60.5% and 52.0-52.2%, respectively) produced 1029 by the heat-acid protein coagulation method (Table 2) (Kłobukowski et al., 1997a). The following CaCO 3 was similar around 75.7-79.3% (p > 0.05). There was no significant difference in the extent 1074 of calcium absorption in the tibia for all tested products (between 2.7 and 2.9%). Caucasian women, and no significant difference was observed between pasteurized and 1086 homogenized cow's milk (32.8%), Cheddar cheese (37.4%), yoghurt (24.2%) and processed cheese 1087 (33%) (Nickel et al., 1996). In the second study in healthy postmenopausal women, calcium 1088 absorption was not significantly different between whole milk (26.7%), chocolate milk (23.2%), 1089 yoghurt (made from whole milk with 2% fat) (25.4%), a milk substitute (prepared from milk and 1090 non-dairy products) (22.4%), a cheese (no information about its variety) (22.9%) and calcium 1091 carbonate (22.0%) [START_REF] Recker | Calcium absorbability 1626 from milk products, an imitation milk, and calcium carbonate[END_REF]. ). Urinary excretion of 1103 calcium is higher (+ 0.5 mmol/day) with water than with milk (p < 0.001), suggesting that calcium 1104 balance is better with milk intake than with SO 4 -rich water. The acidogenic action of SO 4 would be 1105 responsible for this effect. In the study by Couzy et al. the bioavailability of milk calcium (UHT sterilized, 2.8% fat) is 1107 compared to that of mineral water in healthy young women [START_REF] Couzy | 1418 Calcium bioavailability from a calcium-and sulfate-rich mineral water, compared with milk, in 1419 young adult women[END_REF]. The fractional 1108 absorption of calcium from milk (25%) did not differ significantly from that of mineral water without cholecalciferol, and from milk (no data on applied technological treatments) in young 1132 women (mean age 30 years) and a group of elderly people of both sexes (mean age of 66 years) 1133 (Hitz et al., 2005). Each diet contains 1200 mg of calcium. Taking into account all participants, 1134 urinary excretion rates (mmol/day) of calcium were 4.41 for the placebo group (tablets), 5.17 for (Fardellone et al., 1993). varies in adult between 25 and 35%; 2) Even if it is sometimes difficult to extrapolate to human the 1206 results obtained in rats or in vitro, at least it can be seen that calcium is as bioavailable, or even 1207 more, in cheeses than in milk; 3) Recent data in humans are few. They show that the calcium 1208 absorption of a cooked pressed cheese is significantly higher than that of calcium from various 1209 plants (Falcou and coll., 1988); and that the comparison between various dairy products and 1210 calcium carbonate confirmed the good intestinal absorbability of calcium in cheese, equivalent to 1211 that of carbonate [START_REF] Recker | Calcium absorbability 1626 from milk products, an imitation milk, and calcium carbonate[END_REF].

1212

Guéguen continued: « The absorbability of calcium in cheese thus seems good and 1213 equivalent to that of calcium in milk, despite the differences in constituents that could theoretically 1214 be unfavorable. Thus, the fact that most cheeses are poor in lactose could theoretically be 1215 unfavorable to calcium absorption, although the relative importance of this beneficial effect of 1216 lactose in a meal has been questioned [START_REF] Gueguen | Calcium bioavailability 1552 from -type cheeses produced by high heat-acid method of milk coagulation[END_REF]. On the other hand, if the 1217 phosphopeptides are likely to increase the in vivo absorption of calcium (which is also debatable), 1218 their presence in a greater proportion in the cheese resulting from the degradation of the proteins 1219 during acidification and ripening should be a favorable factor. Finally, the risk of intestinal 1220 formation of insoluble calcium soaps from the long saturated fatty acids provided by non-lightened 1221 cheeses could be an unfavorable factor. In fact, we have shown that the possible formation of soaps 1222 occurs in the distal small intestine and thus insolubilizes calcium not previously absorbed and 1223 which, in any case, would no longer be so [START_REF] Guéguen | Interactions lipides-calcium alimentaires et biodisponibilité du calcium du 1512 fromage[END_REF]. It seems well established that saturated 1224 lipids do not interfere with the intestinal absorption of calcium, while excess calcium is likely to 1225 decrease absorption of free saturated fatty acids, which is beneficial » (pages 7-8) [START_REF] Guéguen | Calcium du fromage et santé osseuse[END_REF]. 2. It should be noted, however, that the sometimes significant variability of 1252 the apparent absorption percentages for the same product must be attributed to the experimental 1253 conditions more than to true natural variability. The available studies therefore make it possible to 1254 arrive at comparative comparisons and to propose conclusions or certain qualitative trends: 1255 1) The apparent absorption of calcium from fermented milks is higher than that of a normal yogurt 1256 and that of milk; and the bone mineral density of the femur follows the same classification; also 1257 probiotics would increase the solubility of calcium, and increased bacterial production of short-1258 chain fatty acids in the presence of probiotics would increase colonic absorption of calcium ; 1259 2) Milk and yoghurt have similar calcium absorption but higher than cheese; 1260 3) Absorption and retention of calcium is higher for fresh cheese compared to ripened or unripened 1261 cheese; 1262 4) The absorption of calcium from skimmed milk and Cheddar cheese is decreased with aging, 1263 which would correspond to a decrease in calcium requirements of the body; 1264 5) The lipid content of cheese may increase calcium absorption and decrease bone resorption; 1265 6) There is no significant difference in calcium absorption in the tibia for Cheddar cheese (with 1266 different ripening times) and fresh milk; and also for a skim milk, a yoghurt and a goat cheese curd; 1267 7) The ripening time of a cheddar cheese has no significant effect on calcium absorption; 1268 8) There is a correlation between calcium absorption and bone calcium content; 1269 9) In addition to lactose (which may play a role in differences in calcium absorption between dairy 1270 products), lactic acid may play a role in the high bioavailability of calcium in some dairy products. 1271 10) Some recent studies based on bone tests have confirmed the hypothesis formulated in 1992 1272 [START_REF] Guéguen | Interactions lipides-calcium alimentaires et biodisponibilité du calcium du 1512 fromage[END_REF] on the equivalence of milk and cheese for the bone efficiency of calcium (Kato et 1273 al., 2002) [START_REF] Delisle | Biological availability of calcium and magnesium from 1431 dairy products[END_REF]Mora-Gutierrez et al., 2007). The different studies carried out in healthy subjects, except for lactase deficient subjects, suggest 1277 the following conclusions: 1278 1) The absorption of milk calcium is between 17 and 55%, with the majority of studies giving 1279 values between 20 and 30%; which joins the conclusions of the previous review [START_REF] Gueguen | Milk calcium: functions, benefits, requirements and bioavailability -Le 1510 calcium du lait: fonctions, interets, besoins, biodisponibilite[END_REF]; 2) The fractional absorption of milk calcium is similar to that of calcium from mineral water; 1281 3) Cheddar cheese has a fractional absorption of calcium (37%) slightly higher than milk (33%), 1282 processed cheese (33%) and yogurt (24%); 1283 4) The fractional absorption of yogurt calcium seems to be between 15 and 25%; 1284 5) Fresh cheeses (Petit Gervais type) appear to have a higher calcium absorption at around 42%.

1285

In the end, it remains difficult to draw firm conclusions as experimental designs and dairy 1286 products differ from one study to another. However, the fractional absorption of calcium measured 1287 in the rat is generally greater than that measured in humans. Moreover, according to the matrices, it 1288 is probably with the cheeses that the variations of the absorption of the calcium are the strongest, 1289 especially in the rat (Table 2). This is not surprising given the multiplicity of matrices and 1290 nutritional compositions in the large « family » of cheeses. Finally, Dr. Guéguen recalls that "The 1291 absorbability of calcium depends relatively little on its solubility in water, but especially on its 1292 solubility in acid medium (Heaney et al., 1990). If the absorption of calcium from milk is often 1293 taken as a reference, it must be admitted that it is not significantly higher than that of most calcium 1294 mineral salts (carbonate, phosphate, sulfate, chloride, etc.) and is sometimes a little lower than that 1295 of organic salts (lactate, gluconate, citrate, citromalate, etc.). However, differences between good 1296 sources of calcium remain low [START_REF] Gueguen | Calcium bioavailability 1552 from -type cheeses produced by high heat-acid method of milk coagulation[END_REF], the actual absorption coefficient (in 1297 humans) being most often found, under the most favorable physiological conditions, for milk as for 1298 good calcium salts, between 25 and 30% » (page S9) [START_REF] Gueguen | Milk calcium: functions, benefits, requirements and bioavailability -Le 1510 calcium du lait: fonctions, interets, besoins, biodisponibilite[END_REF] -Digestion of yoghurt results in different peptide profiles than milk

In vivo :

-Digestibility ≥ 95%

-Proteolysis during fermentation may lead to the formation of new peptides during gastrointestinal digestion

In vitro :

-More cohesive, compact, elastic and structured cheeses would disintegrate less rapidly during digestion, especially at the gastric level, resulting in slower proteolysis

In vivo :

-Digestibility ≥ 95%

Lipids

In vitro :

-The digested milk contains nearly 41% free fatty acids with respect to the total milkfat (this value corresponded to 100% of the triglycerides) ;

-More short chain fatty acids are released after digestion compared to the relative distribution of total fatty acids in milk before digestion ;

-The size of the lipid droplets influences the kinetics of lipolysis ;

-The initial size of fat globules controls the type of free fatty acids generated but not the degree of

In vivo :

-Fermented milk results in a significantly slower rate of gastric emptying, probably because of higher viscosity ;

-Fermented milk results in a greater increase and a more rapid decrease in the content of triglycerides in all lipoprotein fractions.

In vitro :

-The properties of the cheese matrix influence the access to the lipids of the cheese by controlling the release of the free fat and also via the restriction of the diffusion of the enzyme and the fatty acids ;

-Calcium influences both the structure of the cheese and the kinetics of lipolysis.

In vivo :

-Hard cheeses cause levels of LDL cholesterol, and probably total cholesterol, significantly lower than butter ;

Page 52 of 56 URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and Nutrition In vivo :

-Short-and medium-chain fatty acids are released faster than long-chain fatty acids ;

-The viscosity, the type of emulsion, the size of the particles and possibly also the protein content, influence the digestion and absorption of dairy fat, and probably affects the lipemic response ;

-The small fat globules release probably less atherogenic fatty acids.

-Two different cheeses can have a different impact on total cholesterol.

Calcium

In vitro :

-Calcium is apparently almost completely solubilized, and fermentation of milk could further increase this solubilization ;

-The dialysability of calcium varies from 20 to 28% without apparent effect of the fat content ; -In the presence of cereal products, solubilization of calcium is reduced.

In vivo : rats -The apparent absorption of calcium varies from 74 to 80% ;

-The absorption of calcium is decreased with aging.

In vivo : humans -The absorption of calcium is between 17 and 55%, with a majority of studies giving values between 20 and 30% ;

-The fractional absorption of milk calcium is similar to that of mineral water.

In vitro :

-The dialysability of calcium varies from 28 to 33% without effect of the fat content or the acidity of the products ;

-While the calcium fraction released is about 67%, this fraction is always lower in the presence of cereal products or additives.

In vivo : rats -The apparent absorption of calcium varies from 72 to 83% ;

-The apparent absorption of calcium from fermented milks is higher than that of normal yoghurt and that of milk.

In vivo : humans -The fractional absorption of calcium seems to be between 15 and 25%.

In vitro :

-The calcium dialysability of cheese ranges from 14 to 32%, and may depend on the ratio of phosphorus to calcium (P/Ca).

In vivo : rats -The apparent absorption of calcium varies from 12 to 90% according to cheese matrices ;

-Absorption and retention of calcium is superior for fresh cheese compared to ripened or unripened cheese;

-Calcium absorption of Cheddar cheese is decreased with aging;

-Lipid content may increase calcium absorption and decrease bone resorption;

-The refining time of a cheddar cheese has no significant effect on the absorption of calcium;

-The absorbability of calcium is not increased by the addition of lactose (considered favorable to absorption and absent or in small quantity in most cheeses)

In vivo : humans -There is a high probability that the bioavailability of calcium in cheese will not be different from that of calcium in milk;

-Cheddar cheese has a fractional absorption of calcium (37%) slightly higher than milk (33%), processed cheese (33%) and yogurt (24%);

  yogurt. Authors identified 19 peptides from casein α s1 with raw milk, 16 for 193 pasteurized milk and 51 for yogurt. Finally it was concluded that milk processing increases casein 194 resistance to digestion in the condition of this study.

200

  were similar except for homogenized UHT-sterilized whole milk and UHT-sterilized skim milk 201 which showed a smearing of the bands indicative of new disulfilde bond formation (Wada and same conclusion than in their first study, i.e., « the modification of fat content 298 in cheese, affecting cheese texture and microstructure, could regulate the protein digestion, which 299 may further affect acute protein metabolic response and some physiological functions » (Fang et al., 300 2016b).

310

  Qureshi et al. studied in vitro gastrointestinal protein digestibility of two other types of 311 cheese (Norwegian): the Gamalost (granular cheese, ripened for 10 and 30 days) and the Norvegia

  312

  331secretions. Compared to milk, yogurt delayed intestinal release of liquid phase and of chyme 332 One hour after consumption, 84 and 64% of exogenous nitrogen remained in the

393

  From data collected in minipigs towards the digestion of different dairy matrices, Le 394 Feunteun et al. developed a mathematical model for dairy protein digestion (Le Feunteun et al., 395 2014). For collecting data they used six 18-month-old female adult mini-pigs and six distinct dairy 396 matrices (same as those described in the paragraph above) with identical composition based on a 397 skimmed milk powder. Model was therefore developed to correspond to in vivo data. To summarize 398 the collected data clearly showed that dairy matrix structures impact protein digestion kinetics, and 399 the great differences between amino acid absorption kinetics can be entirely understood by 400 considering the behaviour of dairy matrices in the stomach. Thus the raw rennet gel clearly 401 exhibited the more sustained and low appearance of plasma amino acids while raw milk led to the 402 plasma amino acids only after 20-30 minutes digestion. Other matrices had 403 intermediary behavior but the tendency for amino acid absorption appears to be in decreasing order: 404 milks > acid gels > rennet gels. These results well emphasize that it may exist slow and rapid dairy 405 protein only according to matrix structure, not composition, as was demonstrated earlier with whey 406 versus casein (Boirie et al., 1997). 407 Although composition of infant formula has been significantly improved during the last 408 decade, major differences with the composition and structure of breast milk still remain and might 409 affect nutrient digestion and gut biology. The incorporation of dairy fat in infant formulas could 410 modify their physiological impacts by making their composition closer to that of human milk. The 411 effect of milk fat and milk fat globule membrane (MFGM) fragments in infant formulas on gut 412 digestion, mucosal immunity and microbiota composition was evaluated (Le Huërou-Luron et al., 413 2016). Three formulas containing either (1) vegetable lipids stabilized only by proteins (V-P), (2) 414 vegetable lipids stabilized by a mixture of proteins and MFGM fragments (V-M) and (3) a mixture of milk and vegetable lipids stabilized by a mixture of proteins and MFGM fragments (M-M) were 416 automatically distributed to 42 newborn piglets until slaughter at postnatal day 7 or 28, and 417 compared to a fourth group of sow's suckling piglets used as a breast-fed reference. At both 418 postnatal day, casein and β-lactoglobulin digestion was reduced in M-M proximal jejunum and 419 ileum contents compared to V-P and V-M ones leading to more numerous β-casein peptides in M-M 420 contents. In conclusion, the incorporation of both milk fat and MFGM fragments in infant formula

  472

  texture, cheeses such as Camembert (soft cheese), blue-veined cheese, young 522 and aged Cheddar cheese, and Mozzarella (elastic structure) have different disintegration and 523 digestion patterns during gastric digestion. Thus, the disintegration at the end of gastric digestion is 524 higher when the initial hardness, cohesion and chewability are lower. Thus, Mozzarella, with higher 525 initial cohesion and hardness values, is disintegrated slowly and continuously during gastric 526 digestion. At the end of gastric digestion, elastic-type cheeses (Mozzarella) are about three times 527 less disintegrated in comparison with ripened soft cheeses with a high fat content (Camembert, aged 528 Cheddar); and the release of peptides/proteins, in agreement with the disintegration kinetics, is 529 globally two times lower. Textural properties and structural characteristics such as protein matrix 530 density and fat distribution also affect degradation during the duodenal phase. 531 Concerning Norwegian cheeses Gamalost (grained cheese) versus Norvegia (firm cheese) 532 more peptides are detected in digested Gamalost compared to Norvegia cheese. Moreover, most of 533 the Gamalost peptides are derived from β-caseins, some from casein αs1, and very little from casein 534 αs2 and casein κ. Gamalost and Norvegia cheeses therefore have different protein digestibility 535 profiles, underlining an important "matrix" effect. 536 If we can attempt a first general conclusion on the influence of cheese matrices on 537 proteolysis, it would appear that more cohesive, compact, elastic and structured cheeses disintegrate 538 less rapidly during digestion, especially at the gastric level, resulting in slower proteolysis. This 539 result would be in line with what has been observed with breads, i.e., those with more dense crumb 540 give more time-spreading glycemic responses and have lower glycemic indexes (Burton and 541 Lightowler, 2006; Saulnier and Micard, 2012).

552

  peptide profiles. Whether for milk or yogurt, digestion of β-casein gives a very significant number 553 of peptides covering almost the entire sequence of this protein. It is believed that lactic fermentation 554 is responsible for the formation of new peptides during gastrointestinal digestion. Compared to 555 milk, yoghurt could also delay intestinal nitrogen delivery, but not final absorption. Concerning 556 fermented milks, there is little data: fermentation of milk affects the release of certain amino acids 557 during in vitro digestion. Proteolysis during fermentation can lead to the formation of new peptides 558 during gastrointestinal digestion.

  and derived products 573 Very few studies have investigated in vitro lipolysis of dairy products with different matrix. The 574 first study was led with fresh raw bovine milk submitted to in vitro gastrointestinal digestion 575[START_REF] Gallier | Structural changes of bovine milk fat globules during in 1485 vitro digestion[END_REF]. Briefly fat globules were stable in acidic conditions within stomach due to 576 phospholipids. Then at intestinal level, lipolysis products (released from the hydrolysis of 577 Page 17 of 56 URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and destabilized fat globules and provoked their coalescence or aggregation. 578 Thereafter lipolysis products accumulated to the surface of fat globules forming a lamellar phase. 579 Their solubilisation by bile salts led to the formation of disk-shapes micelles. Finally the free fatty 580 acid release after one hour of gastric digestion and two hours of intestinal digestion followed a 581 logarithmic-type curve (without lag phase), and reached 114 µmol free fatty acids/mL of 582 subsample.

  583

597(

  images during in vitro digestion showing smaller lipid droplets for homogenized HTST-pasteurized 598 whole milks. The fatty acids profiles were also determined but their release was not affected by the 599 processing treatments used in this study.600Finally, the in vitro study byYe et al. provides interesting evidence on the role of the matrix 601 effect of milk by comparing the digestion of the fat globules of a raw native milk and a recombinant 602 milk from skim milk mixed with 4 % of anhydrous milk fat[START_REF] Ye | Effect of the fat globule membrane on in vitro digestion of 1691 milk fat globules with pancreatic lipase[END_REF]. The fat globules in 603 raw milk are coated by natural milk fat globule membrane that is composed predominantly of 604 phospholipids and milk fat globule membrane proteins whereas the fat globules in recombined milk 605 are coated by casein micelles and whey protein. Overall there was a lower lipolysis in the raw milk 606 than in the recombined milk. Authors suggested that « this is probably because of the inhibitory 607 effect of components in the milk fat globule membrane on the activity of lipase »[START_REF] Ye | Effect of the fat globule membrane on in vitro digestion of 1691 milk fat globules with pancreatic lipase[END_REF]. 608 Thus, the conversion of fat globules with their membrane (as in raw milk) into fat globules with 609 superficial layers of casein and serum proteins (as in recombinant milk) increases lipolysis rate of 610 dairy fat, involving an inhibitory effect of the membranes of the fat globules on the hydrolytic 611 action of the pancreatic lipase. In this study authors also reported that the rate and degree of 612 to be influenced by the initial size of the fat globules. Finally after 5 hours of Mu and Porsgaard, 2005) favoring an increased fatty acid release for the control and olein 648 anhydrous milk fat cheeses, both rich in short-and medium fatty acids (Ayala-Bribiesca et al., 649 2017). For high calcium cheeses, the kinetics of lipolysis was significantly different during 650 digestion. Within the first 15 min, lipolysis was significantly increased for olein cheese compared to 651 stearin and was maintained until 240 min. At the end of the duodenal digestion, lipolysis increased 652 for the stearin cheese to reach a similar value than the other cheeses. 653 Lamothe et al. added that although composition factors (total lipid and calcium 654 concentrations) are known to influence the lipolysis rate, the characteristics of the cheese matrix are 655 also an important factor affecting the release of fatty acids, in particular via the restriction of 656 enzyme and fatty acids diffusion[START_REF] Lamothe | Influence of cheese matrix on 1566 lipid digestion in a simulated gastro-intestinal environment[END_REF]. In their study, lipids are released from 657 cheese matrices differently during the gastric phase, with aged Cheddar releasing fats faster than 658 mild Cheddar and Mozzaralla, than light Cheddar, but the release rates are the same after 4 hours of 659 gastroduodenal digestion for all cheeses[START_REF] Lamothe | Influence of cheese matrix on 1566 lipid digestion in a simulated gastro-intestinal environment[END_REF]. Authors explained that the stronger, 660 denser and more cohesive matrix structure of light Cheddar could explain the lower rate of lipid 661 digestion relative to other cheeses during gastric digestion. In addition free oil was strongly 662 correlated with cheese disintegration during the different stages of cheese digestion. However, 663 concerning free fatty acid release following lipid hydrolysis during the duodenal digestion the 664 higher moisture and lower fat content of light Cheddar cheese make it easier for the enzymes to 665 diffuse within the cheese matrix and react with fat droplets. On the contrary, according to authors 666 the much lower degree of cohesion of aged Cheddar could promote matrix disruption into fine 667 particles for which the greater firmness and lower porosity could contribute to the resistance of 668 lipids to lipase attack. Then the greater extent of matrix disruption for aged Cheddar probably 669 explains why its rate and extent of free fatty acids production were slightly greater after 60 min of 670 duodenal digestion compared to mild Cheddar.

  homogenization on gastric lipolysis was studied by investigating the semi-dynamic 677 gastric in vitro digestion of three matrices (three model infant formulas): a standardized milk 678 emulsion containing native milk fat globules referred to as minimally-processed emulsion, and two 679 processed model infant formulas (homogenized or homogenized/pasteurized) (Bourlieu et al., 680 2015). Gastric conditions mimicked those reported in newborns. The minimally-processed emulsion 681 was lipolyzed and proteolyzed slower than processed formulas. The difference in initial structure 682 digestion. The surface of the droplets was the key parameter to control gastric 683 lipolysis kinetics; it ranged from 1.81 m²/g of lipid for minimally-processed formula to 31.90 m²/g 684 of lipid for the most processed one. The pattern of released fatty acids and proteolysis by faster 685 hydrolysis of adsorbed proteins was also significantly affected by homogenization. the study by Fruekilde et al. was to examine in the rat for the effects of the 689 physicochemical properties of dairy products on lipid absorption at the lymphatic level (Fruekilde 690 and Hoy, 2004). Although with very different fat contents (21 to 80%), the five dairy products 691 tested (cream cheese, cream, sour cream, butter and melted butter) differ little in terms of their fatty 692 acid composition. Administration of cream and sour cream leads to a faster absorption of the lipid 693 fraction at the lymphatic level than with cream cheese, butter and melted butter, and a higher 694 cumulative absorption after 8 hours. The lymphatic absorption of the fat after administration of the 695 cream cheese is similar to the absorption after consumption of butter and melted butter for up to 4 696 hours; then it increases to a level between that obtained with the consumption in the rat of cream or 697 sour cream, and of butter or melted butter. Overall, these results demonstrate different profiles of 698 lymphatic absorption of dairy fat by their physicochemical properties. Because the fatty acid 699 composition of dairy products differs only slightly, this indicates that the viscosity, the type of 700 emulsion, the particle size and possibly also the protein content, influence the digestion and 701 absorption of the dairy fat, and probably affects the lipemic response.

712

  After 4 h there was no difference in serum increases in triglyceride concentrations and in the 713 triglyceride iAUC 0-8 h (area under curve) for the three dairy matrices. The most notable result was 714 the significantly higher triglyceride response induced by the cream cheese (change from baseline: 715 +44%) than those induced by butter (change from baseline: +24%) and cheddar cheese (change 716 from baseline: +16%). According to authors the fat globule organization within cheese matrices the postprandial lipid response. In effect homogenization of the cream cheese 718 increases the number and stability and decreases the size of lipid droplets. Thus, the diameter of a 719 lipid droplet from cream cheese is ≈0.5 µm, approximately one-sixth the size of a cheddar cheese 720 lipid droplet (≈3.0 µm), increasing contact surface for lipase.The second study has been led during 8 weeks in 153 Norvegians aged above 18 years with 722 (n = 44) and without (n = 102) metabolic syndrome(Nilsen et al., 2015). The subjects were divided 723 into three groups: 1) Gamalost cheese (50 g/day) which is a traditional Norwegian skimmed milk 724 cheese naturally free of salt and fat, containing only 160 mg calcium/100 g, and which has a high 725 protein content and a high amount of bioactive peptides; 2) Norwegia, a gouda-type cheese (n = 50) 726

  751

  a randomized cross-sectional study compared in 49 healthy adult males and females 752 the effects of daily consumption of hard cheese (Samsø with 27% fat) for 6 weeks compared to 753 butter (bringing the same amount of lipids, accounting for 13% of energy intake) (Hjerpsted et al., 754 2011

780 1981 )

 1981 were compared to milk towards lipemia. The study by Sanggaard et al. had the main 781 objective of comparing the effects of whole milk and fermented whole milk (with a mixture of 782 Lactobacillus acidophilus and Lactococcus cremoris) on postprandial lipid and carbohydrate 783

  milk results in a greater increase and a more rapid decrease in the triglyceride 787 content in all lipoprotein fractions (LDL fractions, p < 0.005; other fractions HDL, VLDL and 788 chylomicrons, p < 0.001). The more prolonged and lower triglyceridemic response to milk 789 consumption may be due to coagulation of milk in the stomach. These effects were attributed to the 790 higher viscosity of the fermented milk and could therefore be applied to fresh cheeses. Finally, 791 Rossouw et al. conducted a short, 3-week randomized controlled study in 32 healthy adolescents 792 who consumed 2 liters of skimmed milk, yoghurt or whole milk cream per day (Rossouw et al., 793 1981) in addition to their usual diet. Compared with pre-intervention values, plasma LDL-794 cholesterol concentrations were reduced in the skimmed milk group but increased in the yoghurt 795 and cream groups. 796 Finally in a randomized controlled trial, eight hospitalized tube-fed preterm infants were 797 their own control to compare the gastric digestion of pasteurized human milk and of homogenized 798 pasteurized human milk. Pasteurized human milk was obtained from donors and, for half of it, was 799 homogenized by ultrasonication (de Oliveira et al., 2017). Over a six-day sequence, gastric aspirates 800 were collected twice a day, before and 35, 60 or 90 min after the start of pasteurized human milk or 801 homogenized pasteurized human milk ingestion. The impact of homogenization on pasteurized 802 human milk digestive kinetics and disintegration was tested using a general linear mixed model. 803 Results were expressed as means ± SD. Homogenization led to a six-fold increase in the specific 804 surface (P < 0.01) of lipid droplets. The types of aggregates formed during digestion were different 805 between pasteurized human milk and homogenized pasteurized human milk, but the lipid fraction 806 kept its initial structure all over the gastric digestion (native globules in PHM vs. blend of droplets 807 in PHHM). Homogenization increased the gastric lipolysis level (p < 0.01), particularly at 35 and 808 60 min (22 and 24% higher for homogenized pasteurized human milk, respectively).809Homogenization of pasteurized human milk increased the gastric lipolysis level. This could be a 810 potential strategy to improve fat absorption, and thus growth and development in infants fed with 811 pasteurized human milk; however, its gastrointestinal tolerance needs to be further investigated.

  821

  the viscosity of different cheeses (soft fresh cheeses versus hard cheeses in particular) 822

852 3 )

 3 Two different cheeses can have a different impact on total cholesterol; 853 4) A Camembert and a whole yogurt give similar cholesterolemia; 854 5) Compared to native milk, fermented milk results in a slower gastric emptying than liquid 855 milk, as well as a higher increase and a faster decrease in triglyceride levels in all plasma 856 Page 25 of 56 URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and These effects were attributed to the higher viscosity of the fermented 857 milk and could therefore be applied to fresh cheeses; 858 6) While the physical structure of the different dairy products does not appear to have a major 859 effect on plasma levels of postprandial triglycerides, it is still able to influence the time of 860 onset of the triglyceride peak, and gastric emptying time does not seem to play a major role 861 in modulating the triglyceridemic postprandial response.

  are measured only the bioaccessibility or the solubilisation of the calcium: the percentages 867 do not reflect in any way the actual bioavailability of calcium in vivo. However, they may give an 868 indication of its potential absorbability by the intestine, notably after dialysis.

869

  In the study byUnal et al. several dairy products purchased from local Turkish supermarkets 870

889

  In the Cameroonian study of Ngounou et al. wild strains of Streptococcus thermophilus and 890 Lactobacillus bulgaricus, isolated from Cameroonian zebu milk, were used to ferment skimmed 891

898

  characterization in order to better define their contribution to the quality of the local fermented 899 milks. 900 In their review of 2014, Klobukowski et al. recalled that in an in vitro experiment carried 901 out in 2005 all the calcium in the milk was released in solution after digestion (Klobukowski et al., 902 2014). Then, Klobukowski et al. briefly reported the results of a study conducted in 2005 but 903 unpublished with respect to the solubilization of milk calcium in the presence of cereal products. 904 Breakfasts based on milk alone or with cereal products were digested in vitro. Almost all calcium 905 from milk alone is released in solution. However, while corn and barley flakes and semolina 906 slightly decrease the amount of calcium measured in solution after digestion, wholemeal bread and 907 rolls retain about 50% of the calcium; which is a surprise for the authors as the rolls were made 908 from white flour. Then the authors reported the results of an earlier in vitro digestion study by 909 Skibniewska et al. wherein the calcium solubility of a commercial yoghurt was measured in the 910 presence or absence of cereal products (i.e., corn flakes, wheat flakes, muesli, oat flakes, wheat and 911rye bread slice, and slice of wholemeal bread)[START_REF] Skibniewska | Calcium availability from yogurt by itself or yogurt-cereal-containing products[END_REF]. While the calcium 912 fraction released from the yogurt after digestion is about 67%, this fraction is always lower in the 913 presence of any cereal products, i.e., from about 38 (oat flakes) to 65 % (slice of wheat and rye

938

  The study byBuchowski et al. has compared the bioavailability of double-labeled calcium 939 from different dairy matrices, i.e., skimmed milk, yoghurt and fresh cheese curds (Buchowski et al., 940 1989). The radiolabeling was carried out intrinsically on goat milk with 45 Ca (injected into the 941 jugular vein of the goat) and extrinsically (calcium solution added before the final incubation of 24 942

  945 absorption (3.3-3.5%) of47 Ca. Expressed as a percentage of the dose administered, absorption of 946 47 Ca was also strongly correlated with bone content in 47 Ca and 45 Ca (R = 0.923 for the correlation 947 between the 47 Ca and 45 Ca content of the tibia). For each product tested, the extrinsic 47 Ca was 948 absorbed similarly to the intrinsic 45 Ca. Finally, the percentage of radioactive dose retained in bone 949 appears to be a valid indicator of the relative bioavailability of dietary calcium.

950

  In the study by Poneros et al. dried skimmed milk powder, freeze-dried Mozzarella cheese 951

959

  In the study byKaup et al. several groups of rats have received different diets in which the 960 calcium carbonate provides either the whole of the calcium or half which is then added half by 961 dried skimmed milk with or without lactic acid, 2) traditional yogurt (cultured with 962

  the El-Gawad et al. study was to evaluate and compare the effect of cow's milk 1000 (3.2% fat) and various yogurts with (Bifidobacterium lactis Bb-12 or Bifidobacterium longum Bb-1001 46) or without probiotics on the bioavailability of calcium and bone mineralization in 48 male 1002 albino rats fed 45 days (El-Gawad et al., 2014). The serum calcium levels did not differ 1003 significantly between the different dairy matrices. However, the highest apparent calcium 1004 absorption was observed in rats fed the yogurt-based diet cultured with Bifidobacterium lactis Bb-1005 12 (83%) followed by the yogurt cultured with Bifidobacterium longum Bb-46 ( 82%), plain yogurt 1006 (78%) and cow's milk (76%). The authors suggest that peptides released by the degradation of 1007 caseins by digestive enzymes can promote the absorption of calcium by intestinal cells by 1008 preventing the precipitation of insoluble salts (Meisel et al., 2003). Otherwise, bone mineral density 1009 of the femur is significantly higher with yogurt cultured with Bifidobacterium lactis Bb-12 1010 compared to other dairy matrices. Moreover, the rupture force of the femur does not differ 1011 according to the matrices. According to the authors, the suggested mechanisms of the positive effect 1012 of probiotics on mineral bioavailability and bone properties may include: 1) increased mineral 1013 solubility due to increased bacterial production of short-chain fatty acids, and 2) enlargement of the 1014 absorptive surface due to the promotion of enterocyte proliferation mediated by bacterial 1015 fermentation products

  cheese have been tested in rats for their calcium bioavailability. First, based on 1022 studies in animals,Klobukowski et al.

  out in the rat, tested the absorption of calcium from a white cheese supplemented or in rats from CaCl 2 (28 mM), CaCO 3 , milk (fresh and adjusted to pH 5.35 1066 -Cheddar pH) and Cheddar cheeses (≈35% fat) ripened for various periods -using double-labeled 1067 cheeses with 45 Ca and 47 Ca(Buchowski and Miller, 1990). The cheeses were made from pasteurized 1068 cow's milk. The bioavailability of calcium was determined by two methods: 1) the measured 1069 absorption based on the whole body radioactivity count; and 2) availability for bone metabolism 1070 assessed by bone radioactivity measurements. Calcium absorption varies from 72.8 (Cheddar at 0 1071 day ripening) to 81.2% (Cheddar as a slurry in a lactose solution). The ripening time of the cheese 1072 had no significant effect on calcium absorption. The calcium absorption from milks and CaCl 2 and 1073

  to note that bioavailability studies in humans are generally rather old, probably due 1078 to (1) the development of more recent, cheaper and faster in vitro digestion studies, (2) the high cost 1079 of studies using stable isotopes, (3) non-authorization of radioisotopes, and (3) investment in time 1080 for this type of study. have simultaneously compared milk, yogurt and cheese for their calcium 1084 fractional absorption. In the first one, four different dairy matrices were tested in healthy young 1085

  studies comparing calcium fractional absorption in milk as compared with other 1095 foods or beverages (especially mineral waters), and also calcium carbonate.

  waters 1098 Brandolini et al. recalled that it is well known that the intestinal availability of calcium from 1099 mineral waters rich in calcium is equivalent to that of milk(Brandolini et al., 2005). However, the 1100 Page 32 of 56 URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and anions on urinary calcium losses has not been studied. Their study was carried 1101 out in cross-over in 37 healthy women over a period of 4 x 3 weeks and consuming the same 1102 amount of calcium from a SO 4 -rich milk or mineral water (for anions SO 4 2-

  1106

  during the rapid growth period in 195 healthy girls aged 10-12 years with dietary 1171 calcium intakes < 900 mg/day(Cheng et al., 2005). Four groups involved 1) 1000 mg calcium 1172 carbonate + 200 IU (5 µg) vitamin D daily; 2) 1000 mg calcium carbonate daily + vitamin D 1173 placebo; 3) 1000 mg calcium daily from supplemented dairy products (mainly low-fat cheese); and

  the calcium bioavailability from cheeses has been reviewed and some first conclusions 1204 were already proposed (Guéguen, 2008) : 1) The actual absorption coefficient of calcium in milk 1205 Page 35 of 56 URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and

  based on this review, we propose new updated conclusions for all dairy products and calcium dialysability of cheese varies from 14 to 32%, and may depend on the ratio of 1241 phosphorus/calcium (P/Ca); 1242 5) In the presence of cereal products, solubilization of calcium from milk is reduced: while maize 1243 and barley flakes and wheat semolina slightly decrease the amount of calcium measured in solution 1244 after digestion, wholemeal bread and small rolls retain about 50% of the calcium ; 1245 6) While the calcium fraction released from the yogurt after digestion is about 67%, this fraction is 1246 always lower in the presence of any cereal products, i.e., about 38 (oat flakes) to 65% (slice of 1247 wheat and rye bread).

  of studies in the adult rat the percentages of apparent absorption of calcium are 1251 summarized in Table

  ://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and

  1280

Figure 1 .

 1 Figure legends

F

  of the milk fat cell membrane affects the rate of lipid hydrolysis.

F

  Figure 1.

Table 1

 1

	):

  . The bioavailability of

	Page 29 of 56	Critical Reviews in Food Science and Nutrition
	996	calcium compared to that of the control group receiving calcium sulfate (bioavailability considered
		100%) is higher with milk (113.3%) than with bread (99.4 and 104.4%).
		F o r
		P e
		e r
		R e
		v
		i e
		w
		O
		n l
		y
	995
		30

URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu

  .El-Zahar, K., Sitohy, M., Choiset, Y., Metro, F., Haertle, T., and Chobert, J. M. (2005). Peptic Matar, C., Amiot, J.,Savoie, L., and Goulet, J. (1996). The effect of milk fermentation bySheikh, M. S., Santa Ana, C. A., Nicar, M. J., Schiller, L. R., and Fordtran, J. S. (1987).

	digestibility of their protein fraction (≥ 95%). For the lipid fraction, the data are too still few to
	F o r F o r F o r F o r F o r F o r F o r F o r F o r F o r F o r
	P e P e P e P e P e P e P e P e P e P e P e
	e r e r e r e r e r e r e r e r e r e r e r
	R e R e R e R e R e R e R e R e R e R e R e
	v v v v v v v v v v v
	i e i e i e i e i e i e i e i e i e i e i e
	w w w w w w w w w w w
	O O O O O O O O O O O
	n l n l n l n l n l n l n l n l n l n l n l
	y y y y y y y y y y y
	39 43 47 49

-

  Fresh cheeses appear to have a higher calcium absorption at about 42%; -The calcium absorption of a cooked pressed cheese is significantly higher than that of calcium from various plants. Syntheses and conclusions based on data from the literature presented in this report Calcium apparent absorption from different dairy products as measured in adult rats *

	Page 53 of 56		Critical Reviews in Food Science and Nutrition Critical Reviews in Food Science and Nutrition	Page 54 of 56
	1699
	1700
		Dairy products	Apparent absorption (%)
		Whole cow milk	76, 74-77, 77
	1698	Skimmed milk	15, 69 a , 80
		F o r P e Fresh cheese (acid coagulation) Plain yogurt Probiotic yogurt Ripened cheese Unripened Ricotta cheese White cheese Monterey Jack cheese Cheddar (31% fat) F o r P e e r R e v i e w 15, 72 a , 78 82-83 90 60-76 57-61 90 53 20 Cheddar (7% fat) 12 e r R e Cheddar (35% fat, 0 day ripening) 78 Cheddar (35% fat, 70 days ripening) 73 L'Envol cheese (4% fat) 35 v e i Goat fresh cheese curds 59 a	O n l y
			w
			O
			n l	54
			y

URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu a URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu 55 Tableau 2. * Percentages separated by a comma correspond to separate studies. a Goat milk 1701 1702 Page 55 of 56 URL: http://mc.manuscriptcentral.com/bfsn Email: fergc@foodsci.umass.edu Critical Reviews in Food Science and Nutrition

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additional conclusions can be proposed: