Influence of pasteurization of milk and addition of starter cultures on protein breakdown in ovine cheeses manufactured with extracts from flowers of Cynara cardunculus

Ovine cheeses were manufactured from raw milk (R), pasteurized milk without starter addition (P), and pasteurized milk with starter addition (PS), using in all cases extracts of Cynara cardunculus as rennet and mimicking as far as possible the traditional manufacture process. The microbial counts were higher in R cheeses than in P cheeses, and the lowest microbial counts were found for PS cheeses. Such physicochemical characteristics as moisture, fat, protein, NaCl content, and pH of the three types of cheeses were similar to one another at each sampling time. In particular, pasteurization had no significant effect on protein breakdown as evaluated by either the water-soluble nitrogen, the trichloroaceticacid (TCA)-soluble nitrogen, or the phosphotungstic acid (PTA)-soluble nitrogen fractions. However, the TCA-soluble and the PTA-soluble fractions for the PS cheeses ripened for more than 28 days were higher than those for the R or P cheeses at similar ripening times. The cheeses and their water-soluble extracts could not be distinguished by urea-polyacrylamide gel electrophoresis for up to 7 days, but clear differences were apparent at 68 days of ripening for the PS cheeses with respect to the R and P cheeses.