RAISING THE PH OF THE PEPSIN-CATALYZED HYDROLYSIS OF BOVINE WHEY PROTEINS INCREASES THE ANTIGENICITY OF THE HYDROLYSATES

Background Hypersensitivity to cow milk protein is frequently observed in infancy. Since the pH in the infant's stomach is relatively high ( pH 3-4) compared with adults (pH 2), an incomplete digestion of the mi lk proteins is expected to occur. Objective The determination of the d egree of hydrolysis by pepsin of the four main proteins of bovine whey , i.e. alpha-lactalbumin (alpha La), beta-lactoglobulin (beta Lg), bov ine serum albumin (BSA) and bovine immunoglobulin G (B-IgG), in the pH range 2.0-4.0 and of the antigenic properties of the resulting hydrol ysates. Methods Whey proteins were successively hydrolysed with pepsin at pH values ranging from 2.0 to 4.0 and with pancreatic enzymes at p H 7.5 using a pH-stat. The resulting hydrolysates were characterized b y their degree of hydrolysis, and analysed by sodium dodecyl sulfate p olyacrylamide gel electrophoresis, gel permeation chromatography and i mmunologically by competitive enzyme-linked immunosorbent assay. Resul ts In general, the degree of hydrolysis, the gel electrophoretic patte rns, the contents of peptides of molecular mass > 5 kDa and the residu al human-immunoglobulin E and G antigenicities of the hydrolysates did not differ much whether the pepsin incubation was done at pH 2.0 or 3 .0. Pepsin incubation at pH 4.0, however, resulted in a decreased hydr olysis and enhanced residual antigenicity of alpha La, BSA and B-IgG, but not of beta Lg. Conclusion The poor and slow degradation of the an tigenic epitopes of whey proteins when pepsin digestion occurs under c onditions that prevail in the stomach of infants could be of much impo rtance for the development of cow milk hypersensitivity. The immature gastrointestinal mucosal barrier of infants allows large antigenic fra gments of these proteins to pass into the systemic circulation.