Comparison of the digestion of caseins and whey proteins in equine, bovine, caprine and human milks by human gastrointestinal enzymes

Abstract

-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...

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