A cross-linking approach for studying mutual spatial relationships of protein components in cheese

A cross-linking approach was developed to investigate the distribution of casein components in milk and in commercial cheeses. Cross-linking was carried out with glutaraldehyde, followed by electrophoretic separation of reaction products obtained after different times of exposure to glutaraldehyde. in raw milk alpha(s)-casein and beta-casein showed nearly identical reactivity with glutaraldehyde, while whey proteins did not react. Thus, the method appeared suited to reveal spatial proximity of the reacting proteins. On these bases, the cross-linking procedure was applied to homogenates of 4 commercial cheeses, differing in ripening time, thermal treatment and texture (Mozzarella, Caciotta, Taleggio, and Processed cheese). Kinetics of cross-linking of individual casein components allowed to differentiate among thermally processed and unprocessed ones, with the former giving a reactivity to glutaraldehyde dose to that observed with raw milk. Major differences were found between Taleggio and Caciotta, in which beta-casein and para-kappa-casein seemed the most sensitive indicators of changes in micellar structure associated with cheese ripening.