Influence of Residual Milk-Clotting Enzyme on αs1 Casein Hydrolysis During Ripening of Reggianito Argentino Cheese

Milk-clotting enzyme is considered largely denatured after the cooking step in hard cheeses. Nevertheless, typical hydrolysis products derived from rennet action on α s1 -casein have been detected during the ripening of hard cheeses. The aim of the present work was to investigate the influence of residual milk-clotting enzyme on α s1 -casein hydrolysis in Reggianito cheeses. For that purpose, we studied the influence of cooking temperature (45, 52, and 60°C) on milk-clotting enzyme residual activity and α s1 -casein hydrolysis during ripening. Milk-clotting enzyme residual activity in cheeses was assessed using a chromatographic method, and the hydrolysis of α s1 -casein was determined by electrophoresis and high performance liquid chromatography. Milk-clotting enzyme activity was very low or undetectable in 60°C- and 52°C-cooked cheeses at the beginning of the ripening, but it increased afterwards, particularly in 52°C-cooked cheeses. Cheese curds that were cooked at 45°C had higher initial milk clotting activity, but also in this case, there was a later increase. Hydrolysis of α s1 -casein was detected early in cheeses made at 45°C, and later in those made at higher temperatures. The peptide α s1 -I was not detected in 60°C-cooked cheeses. The results suggest that residual milk-clotting enzyme can contribute to proteolysis during ripening of hard cheeses, because it probably renatures partially after the cooking step. Consequently, the production of peptides derived from α s1 -casein in hard cheeses may be at least, partially due to this proteolytic agent.