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-The aim of this study was to compare the digestion of milk proteins from different species using an in vitro gastrointestinal model. Raw and heated milks from bovine, caprine, human and equine species were digested by human digestive enzymes. Digestion was performed in two 30-min sequential steps by digestive juices from the stomach (pH 2.5/37°C) and from the duodenum (pH 8.0/37°C). The degradation patterns of the milk proteins were visualized by SDS-PAGE and quantified using the ImageQuant program. Caseins in the equine milk were rapidly digested by the gastric juice in contrast to the caseins from the other species. During the subsequent digestion by the duodenal juice most of the caseins from all species were degraded within 5 min, and within 30 min only traces of caseins were detected. The mean casein micellar size varied between species in the range of 146.0-311.5 nm (equine > caprine > bovine > human). The α-lactalbumin from all species appeared to be very resistant to both gastric and duodenal digestions. A similar trend was shown for β-lactoglobulin from bovine and caprine milks, of which~60% intact protein remained, while only 25% remained intact in equine milk after total digestion. Equine milk contained a high amount of lysozyme, of which 60% remained intact in the present study. In heated milks from all species, only α-lactalbumin degradation increased approximately 12-20% in comparison to the raw milk. This study shows that equine milk with fast digestible proteins could be considered as a replacement for bovine milk in the diet of people with special needs, such as infants and the elderly. equine milk / bovine milk / caprine milk / human milk / digestion / whey protein / casein Résumé -Comparaison de la digestion des caséines et des protéines de lactosérum du lait équin, bovin, caprin et humain par les enzymes gastro-intestinales humaines. Le but de cette étude était de comparer la digestion des protéines laitières provenant de différentes espèces en utilisant un modèle gastro-intestinal in vitro. Des laits crus et traités thermiquement des espèces bovines, caprines, équines et humaines ont été digérés par des enzymes digestives humaines. La digestion a été réalisée au cours de deux étapes séquentielles de 30 min par des sucs digestifs gastriques (pH 2,5/37°C) et duodénaux (pH 8,0/37°C). Les profils de dégradation des protéines laitières ont été visualisés par SDS-PAGE et quantifiés à l'aide du programme ImageQuant. Les caséines du lait équin étaient rapidement digérées par le suc gastrique contrairement aux caséines des autres espèces. Au cours de la digestion suivante par le suc duodénal, la plupart des caséines de toutes les espèces étaient dégradées en 5 min, et après 30 min seules des traces des caséines étaient détectées. La taille moyenne des micelles de caséines variait de 146,0 à 311,5 nm selon les espèces (équin > caprin > bovin > humain). L'α-lactalbumine de toutes les espèces apparaissait être très résistante à la fois à la digestion gastrique et duodénale. Une tendance simila...

The objective of this study was to investigate the effects of high and low inhibitor soybean meals on the duodenal enzyme activities and on the possible regulatory role of gastrointestinal hormones in the pancreatic response. After an overnight fast, 11 healthy volunteers received an intraduodenal infusion of saline for 60 min. This was followed by infusion of either of three test meals: extract of raw soybeans (RS), a low inhibitor soy protein isolate (SPI) or bovine serum albumin (BSA), 10 g/h for 60 min. Then saline was again given intraduodenally for 30 min. Gastric juice was collected continuously and duodenal juice and peripheral blood samples were collected every 10 min. Duodenal chymotryptic activity was severely inhibited by RS, whereas SPI and BSA increased the chymotryptic activity. Tryptic activity showed a transient reduction (55%) during RS infusion, whereas BSA and in particular SPI increased the tryptic activity. No change was seen in amylase activity. The lack of total inhibition of tryptic activity has been studied further and is the subject of the accompanying paper. The peripheral plasma levels of cholecystokinin (CCK) increased significantly during BSA but not during SPI or RS infusions. Thus, CCK levels were not increased by the inhibition of the proteolytic activity by RS in duodenal juice.

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The aim of this study was to characterise the individual human gastric and duodenal juices to be used in in vitro model digestion and to examine the storage stability of the enzymes. Gastroduodenal juices were aspirated, and individual variations in enzymatic activities as well as total volumes, pH, bile acids, protein and bilirubin concentrations were recorded. Individual pepsin activity in the gastric juice varied by a factor of 10, while individual total proteolytic activity in the duodenal juice varied by a factor of 5. The duodenal amylase activity varied from 0 to 52.6 U/ml, and the bile acid concentration varied from 0.9 to 4.5 mM. Pooled gastric and duodenal juices from 18 volunteers were characterised according to pepsin activity (26.7 U/ml), total proteolytic activity (14.8 U/ml), lipase activity (951.0 U/ml), amylase activity (26.8 U/ml) and bile acids (4.5 mM). Stability of the main enzymes in two frozen batches of either gastric or duodenal juice was studied for 6 months. Pepsin activity decreased rapidly and adjusting the pH of gastric juice to 4 did not protect the pepsin from degradation. Lipase activity remained stable for 4 months, however decreased rapidly thereafter even after the addition of protease inhibitors. Glycerol only marginally stabilised the survival of the enzymatic activities. These results of compositional variations in the individual gastrointestinal juices and the effect of storage conditions on enzyme activities are useful for the design of in vitro models enabling human digestive juices to simulate physiological digestion.