Digestion of α-Lactalbumin in Rat Gastrointestinal Tracts

The digestion process for α-lactalbumin was investigated and compared with that of ovalbumin using their antigenicity as an index. α-Lactalbumin did not lose its antigenicity by incubation even at high temperature or acidic pH levels. By measuring the residual antigen, α-lactalbumin is shown to be hydrolysed rapidly by pepsin (1:66) or pancreatin (1:25) in vitro without any previous denaturation treatment. The α-lactalbumin antigen also rapidly disappeared in the gastrointestinal tracts of rats. One hour after administering 250 mg of whey protein which contained 42 mg of the α-lactalbumin antigen, the α-lactalbumin antigen remaining in the stomach was only 3.95±0.4 mg. In the small intestine, a trace amount of the antigen was detected. In more distal parts of the tract, no antigen was found. Rapid gastric emptying was achieved by using α-lactalbumin in a 0.9% NaCl solution without carbohydrate and lipids. However, the antigen recovered from the small intestine remained at a trace level. Thus the capacity for α-lactalbumin digestion in the small intestine may be very large. In the previous examination, a significant amount of the intact ovalbumin antigen was detected in the stomach and small intestine. These results suggest that the digestion of α-lactalbumin measured by the disappearance of its antigen is significantly different from ovalbumin digestion.