Differential influence of the degree of processing on immunogenicity following proteolysis of casein and -lactoglobulin

Simulated gastric fluid digestion was used to investigate how heat processing and fat content influence effects of proteolytic digestion on milk protein immunogenicity in milk with varying fat content and degree of processing. Changes in antigenicity and allergenicity of casein and -lactoglobulin (-LG) were demonstrated, using polyclonal antibodies and milk-allergic patient sera in immunoblot and enzyme-linked immunosorbent assay (ELISA) inhibition. Heat-induced changes in ultra-high temperature processed (UHT) milk increased stability of IgE and IgG casein epitopes to digestive proteolysis, but had little effect on specific IgE or IgG binding. Native -casein may be more resistant to digestion, but this was abrogated by heat treatment. Although -LG's digestive stability decreased in UHT milk, immunogenicity was retained after hydrolysis in both processed (UHT) and non-processed (semi-skimmed) milks. Differences in fat levels in three milk matrices which had been processed similarly did not appear to influence digestibility. The possible clinical significance of these findings remains is discussed.