Effect of starters on proteolysis of Graviera Kritis cheese

Abstract

Four cheesemakings of Graviera Kritis cheese (cheeses A-D) were made from a mixture of ewe's and goat's milk. Three of these were made with mixed cultures of thermophilic + propionie 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 tractions 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 pII4.4-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 mmol-kg-1 after 180 d of ripening. The changes in total FAA and in the most abundant FAA during the ripening were significantly correlated with cheese age (r > 0.940). The ripening at higher temperature increased the main FAA and the total FAA content in all types of cheeses, in particular in the cheese made without starter cultures. © Inra/Elsevier, Paris.