Effects of ripening time and combination of ovine and caprine milks on proteolysis of Picante cheese

Proteolysis in Picante cheese was characterized by assaying for breakdown products throughout a 180 day ripening period using different combinations of ewe's and goat's milks. Parameters analysed were total nitrogen (TN), water-soluble nitrogen (WSN) and non-protein nitrogen (NPN) using Kjeldahl and spectro-photometric methods, and casein profile by electrophoresis. WSN at 180 days of ripening was 25-29% TN. The maximum NPN values were attained by 180 days of ripening and corresponded to 87% and 92% of the WSN in 0C and 100C, respectively (where iC denotes a cheese manufactured with i% caprine milk). Statistically significant correlations were obtained between the various analytical methods of assay for nitrogen and ripening time. The spectrophotometric methods using either trinitrobenzenesulphonic acid or cadmium-ninhydrin proved satisfactory in assessing the ripening index (instead of the Kjeldahl method). Degradation of β-caseins at 180 days was 18.8, 26.4, 40.2, 55.6 and 36.5% for 0C, 25C, 50C, 75C and 100C, respectively. Degradation of α(s)-caseins by 180 days was 35.9, 40.2, 81.8, 93.0 and 68.7% for 0C, 25C, 50C, 75C and 100C, respectively. In general, a higher cheesemaking milk fraction of caprine milk was associated with higher amounts of γ-caseins.