Increase in degranulation of mucosal mast cells in rats sensitized with milk whey protein hydrolysates compared with native proteins

The allergenicity of two types of whey protein hydrolysates-bacterial protease hydrolysed whey protein (BHW) with a molecular mass less than 3500 and trypsin hydrolysed whey protein (THW) with a molecular mass less than 6500-was compared with that of whey protein concentrate (WPC) or β-lactoglobulin (β-LG) in vivo by their ability to release rat chymase II (RChyII), an indicator of muccsal mast cell degranulation in the intestine. Antigen-specific reaginic activity and immunoglobulin (Ig)G in serum were markedly lower in rats primed with BHW than in those with WPC or β-LG, although these were not lowered in THW-primed rats. In contrast, rats primed with either hydrolysate and subsequently orally challenged with the primed antigen increased the release of RChyII to a greater extent than did rats primed and challenged with the native proteins. The extent of the release was primarily attributed to the nature of primed rather than challenged antigen. These results indicate that determination of circulatory RChyII is a sensitive in vivo method to evaluate the allergenicity of milk protein hydrolysates. The improper hydrolysis of dietary protein may enhance allergic reactions.