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Influence of Residual Milk-Clotting Enzyme on _s1 Casein Hydrolysis During Ripening of Reggianito Argentino Cheese

Programa de Lactología Industrial, Facultad de Ingeniería Química, Universidad Nacional del Litoral, Santiago del Estero 2829, S3000AOM Santa Fe, Argentina

Corresponding author: E. R. Hynes; e-mail: ehynes{at}fiqus.unl.edu.ar.

Milk-clotting enzyme is considered largely denatured after the cooking step in hard cheeses. Nevertheless, typical hydrolysis products derived from rennet action on _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 _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 _s1-casein hydrolysis during ripening. Milk-clotting enzyme residual activity in cheeses was assessed using a chromatographic method, and the hydrolysis of _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 _s1-casein was detected early in cheeses made at 45°C, and later in those made at higher temperatures. The peptide _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 _s1-casein in hard cheeses may be at least, partially due to this proteolytic agent.

Key Words: milk-clotting enzyme • hard cooked cheese • proteolysis • _s1-casein

Abbreviation key: CMP = casein macro peptide, CT = cheeses in which the cooking step was performed at control temperature (52°C), HT = cheeses in which the cooking step was performed at high temperature (60°C), LT = cheeses in which the cooking step was performed at low temperature (45°C), PC = principal component, PCA = principal component analysis

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