Heat treatment of cheese milk: effect on proteolysis during cheese ripening

Two batches of rindless cheese of the type Danbo 45 + (semi-hard cheese with 45% fat in dry matter) were manufactured from milk subjected to heat treatment at 72 degreesC, 80 degreesC or 90 degreesC for 15, 30 or 60 s. The effect of heat treatment on the proteolytic process in the cheeses during a 16-week ripening period was monitored by the use of reversed phase HPLC analysis of pH 4.6 soluble peptides. Peak-areas from peptide profiles were calculated essentially in 5-min intervals, and the resulting areas as well as the total peak-area were examined using principal component analysis (PCA). This resulted in a PCA-model with 5 principal components (PC) which accounted for more than 83% of the total variance in the data. Score plots revealed that PCI separated the cheese samples mainly according to temperature of cheese milk heat treatment, whereas it was found that PC2 separated the samples mainly according to variations in age and trial number. The results were in agreement with observations on plasmin activity and digestion of casein in the experimental cheeses during the ripening period. To verify these observations it was shown that regions in the peptide profiles displaying large variation between cheeses manufactured from milk heated at low and high temperatures, respectively, included peptides created by plasmin digestion of casein. (C) 2001 Elsevier Science Ltd. All rights reserved.