Effect of starters on proteolysis of Graviera Kritis cheese

Four cheesemakings of Graviera Kritis cheese (chee ses A-D) were made from a mixture of ewe' s and goal' s milk. Three of these were made with mixed cultures of thermophilic + propionic or mesophilic + thermophilic + propionic starters, while the fourth one was made traditionally without starter cultures. The effect of increasing the temperature of ripening was also determined. The pH 4.4-soluble nitrogen (SN) and trichloroacetic acid (TCA-SN) fractions increased mainly during the warm room ripening. The use of starters caused no significant differences in the ratios of nitrogen fractions of the four mature cheeses (age> 90 d), whatever the ripening temperature. Nitrogen fractions were significantly correlated with cheese age. At 180 d of ripening, the percentage of pH 4.4-SN in total nitrogen (TN) was 20.7-22.8 % and that of TCA-SN in TN was 19.1-19.3 %. Polyacrylamide gel electrophoretic (PAGE) results showed that chymosin and plasmin action was intense during the maturation of the cheeses. The proportion of hydrophilic peptides was higher in the water soluble nitrogen (WSN) fraction of the cheeses made with starter cultures at both ripening temperatures. Free amino acids (FAA) were not significantly different in the four types of cheeses, reaching 208-246 mmolkg-' after 180 d of ripening. The changes in total FAA and in the most abundant FAA during the ripening were significantly correlated with chee se age (r > 0.940). The ripening at higher temperature increased the main FAA and the total FAA content in ail types of cheeses, in particular in the chee se made without starter cultures. InralElsevier, Paris.