Detection of pH 4.6 insoluble beta-lactoglobulin in heat-treated milk and Mozzarella cheese

Different protein aggregates including beta-lactoglobulin (beta-lg) were detected in the pH 4.6 insoluble fraction recovered from actual heat-treated milk samples by gel electrophoresis and immunoblotting. A competitive enzyme-linked immunosorbent assay (ELISA) using anti-beta-lg polyclonal antibodies was developed to analyze the beta-lg partition in the protein fractions obtained upon acidification of both milk and Mozzarella cheese at pH 4.6. According to ELISA determinations, nearly 90% of the pH 4.6 soluble beta-lg included in raw milk was found in the pH 4.6 insoluble fraction of ultrahigh temperature (UHT)-treated milk. As concerns Mozzarella cheese analysis, ELISA results indicated that about 36% of the total beta-lg milk content was transferred from pasteurized milk to Mozzarella cheese, whereas less than 0.5% was transferred from raw milk. The pH 4.6 insoluble beta-lg proved to be a suitable indicator of the intensity of the heat treatment applied to milk. The ELISA-based detection of this parameter was suggested for quality control of both drinking milk and raw milk cheese.