Cheddar cheese production, structure and in-vitro semi-dynamic gastric digestion: The role of β-casein phenotype

The objective of this study was to establish the impact of β-casein A1/A1, A1/A2 and A2/A2 phenotypes on the cheese-making process, cheese structure and on the subsequent in vitro gastric digestion properties of the cheese samples. The time required for curd cutting in cheese milk containing β-casein A2/A2 was significantly delayed, compared to milks containing β-caseins A1/A1 and A1/A2. After 180 days of ripening no differences were observed in the level of soluble nitrogen at pH 4.6 between any of the cheese samples, with a decrease in the level of aggregated β-sheets and increase in the level of β-turns and random coils observed in all cheese over the ripening period. During simulated gastric digestion, cheese samples took between 15 and 20 min to form the initial digesta coagulum, which occurred between pH 4.3 and 4.0. The rate of protein breakdown was slower in A2/A2 cheese, with less cheese structure degradation occurring, compared to β-casein A1 containing cheeses. This study has shown that rennet coagulation takes significantly longer in cheese milk containing only β-casein A2/A2, and that there was less protein breakdown during its simulated gastric digestion.