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

摘要

The digestion of milk proteins from various species using an in vitro gastrointestinal model was compared. Raw and heated (95 degrees C, 1 min) samples of cows' milk (pasteurized skim milk), goat milk, human milk and mares' milk were digested by human digestive enzymes. Digestion was performed in 2 x 30 min sequential steps by digestive juices from the stomach (pH 2.5/37 degrees C) and from the duodenum (pH 8.0/37 degrees C). The degradation patterns of the milk proteins were visualized by SDS-PAGE and quantified using the ImageQuant program. The casein fraction of mares' milk was rapidly digested by the gastric juice in contrast to the casein fraction from the other species. During the subsequent digestion by the duodenal juice most of the casein fraction from all 4 species were degraded within 5 min, and within 30 min only traces of casein were detected. The mean casein micellar size varied between species in the range of 146.0-311.5 nm (equine > caprine > bovine > human). alpha-Lactalbumin from all species appeared to be very resistant to both gastric and duodenal digestions. A similar trend was shown for beta-lactoglobulin from mares' milk or the goat milk, of which approx. 60% protein remained intact, while only 25% remained intact in mares' milk after total digestion. Mares' milk contained a high amount of lysozyme, of which 60% remained intact. In heated milk samples from all species, only alpha-lactalbumin degradation increased approx. 12-20% in comparison with digestion of raw milk. It is suggested that mares' milk with fast digestible proteins could be considered as a replacement for cows' milk in the diet of people with special needs, such as infants and the elderly.