Raising the pH of the pepsin-catalysed 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 milk proteins is expected to occur.

Objective: The determination of the degree of hydrolysis by pepsin of the four main proteins of bovine whey, i.e. alpha-lactalbumin (alpha La), beta-lactoglobulin (beta Lg), bovine 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 hydrolysates.

Methods: Whey proteins were successively hydrolysed with pepsin at pH values ranging from 2.0 to 4.0 and with pancreatic enzymes at pH 7.5 using a pH-stat. The resulting hydrolysates were characterized by their degree of hydrolysis, and analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, gel permeation chromatography and immunologically by competitive enzyme-linked immunosorbent assay.

Results: In general, the degree of hydrolysis, the gel electrophoretic patterns, the contents of peptides of molecular mass > 5 kDa and the residual 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 hydrolysis and enhanced residual antigenicity of alpha La, BSA and B-IgG, but not of beta Lg.

Conclusion: The poor and slow degradation of the antigenic epitopes of whey proteins when pepsin digestion occurs under conditions that prevail in the stomach of infants could be of much importance for the development of cow milk hypersensitivity. The immature gastrointestinal mucosal barrier of infants allows large antigenic fragments of these proteins to pass into the systemic circulation.