No abstract

-A lamb rennet paste preparation was studied to determine its suitability for the manufacture of the three main Spanish raw ewe's milk cheeses with Protected Designation of Origin (Manchego, Idiazabal and Zamorano) from the hygienic and sensory points of view. Cheeses were manufactured with lamb rennet paste or with commercial rennets (bovine powder rennet for Manchego cheese and liquid lamb rennet for Zamorano and Idiazabal cheeses) at identical levels of coagulating strength. Free fatty acids and partial glycerides were also analysed to study lipolysis levels and to relate them to sensory properties. No statistically significant differences were detected in microbiological counts for any of the species analysed between cheeses manufactured with lamb rennet paste and cheeses manufactured with non-paste commercial rennet. We conclude that the hygienic quality of the cheeses made in this study with lamb rennet paste was comparable with that of cheeses made with non-paste commercial rennet. Cheeses made with lamb rennet paste showed a higher lipolysis level than cheeses made with non-paste commercial rennet. Sensory differences between cheeses made with either type of rennet were mainly detected in Idiazabal cheese, whereas the sensory profile of the cheeses made with lamb rennet paste or with non-paste commercial rennet was rather similar for Manchego and Zamorano cheeses. Idiazabal cheeses manufactured with lamb rennet paste showed the highest scores for odour and flavour intensities, sharp odour, rennet odour and flavour, butyric flavour and pungent character. On the other hand, Idiazabal cheeses made with non-paste commercial rennet had higher scores for milk and buttery odour attributes than cheeses made with lamb rennet paste.

The use of artisan-produced lamb rennet pastes, but not any of the other commercial animal rennets, imparts a characteristic flavour to the cheese, so most Mediterranean ewes' milk cheeses are coagulated with this kind of rennet paste. In contrast to the advantages of using lamb or kid rennet pastes from the sensory point of view, questions are still raised as to their hygienic quality. The goal was to examine the microbiological and enzymic quality of lamb rennet pastes prepared by cheese manufacturers for their own use, and evaluate the hygienic quality of raw sheeps' milk cheeses made with them, using Idiazabal cheese as a model. Lamb rennet pastes prepared by artisan cheese makers from the Basque region of Spain (27), and Italy (8) were evaluated. For cheese making experiments 5 different lamb rennet pastes were selected among the 27 samples from the Basque Country region of Spain. Microbiological analyses were carried out on samples from rennet pastes, rennet extracts, milks and cheeses during ripening. Enzymic activities studied in rennet paste were: total coagulating strength and lipase. Analysis of variance and Student's t-tests was performed. The results show that the artisan-produced rennet pastes contain high levels of a variety of microorganisms. After 60 ripening days, which is the minimum ripening period required for Idiazabal cheese prior to its commercialization, no Eschericia coli, Clostridium, Salmonella spp. or Listeria monocytogenes were detected, and levels for the rest of the microorganisms were below the limits of the European legislative standards for cheese manufactured with raw milk. We can conclude that the use of artisan-produced lamb rennet pastes of questionable hygienic quality for the manufacture of raw milk hard cheeses yields products of good hygienic quality.