Effects of ventilation rate and of dietary protein level in an intensive dairy sheep system on the features of Canestrato Pugliese cheese

Abstract

Effects of ventilation rate and of dietary protein level in an intensive dairy sheep system on the features of Canestrato Pugliese cheese were studied. Cheeses were manufactured from the bulk milk obtained from ewes subjected to four different experimental treatments: (1) low dietary crude protein (CP) of 13% in dry matter (DM) at a low ventilation rate (23·5 m³/h per ewe) (LPLV); (2) low dietary CP at a moderate ventilation rate (47 m³/h per ewe) (LPMV), (3) moderate dietary CP of 16% DM at a low ventilation rate (MPLV); and (4) moderate dietary CP dietary at a moderate ventilation rate (MPMV). Bulk milk and cheeses (at 1, 15, 45 and 90 d of ripening) were analysed for chemical composition, N fractions and plasmin-plasminogen activities. The pH 4·6-soluble and insoluble N fractions were analysed by urea-PAGE. Bulk milk from ewes receiving the low CP diet displayed higher casein and lower urea contents. Ewes subjected to the low ventilation rate displayed a higher plasminogen activity in milk, whereas no differences emerged among treatments in the conversion of zymogen to plasmin. During ripening the plasmin-plasminogen system in cheese did not display significant changes across treatments. At 90 d of ripening, the cheese produced with milk from ewes receiving the low CP diet and exposed to the low ventilation rate displayed more markedly stained bands in the area of γ-caseins in pH 4·6-insoluble N fraction. As from 15 d of ripening, the pH 4·6-soluble fraction showed a greater number of bands in the LPMV and MPMV than in the LPLV and MPLV cheeses. The results showed that Canestrato Pugliese cheese manufactured with milk from ewes fed the low CP diet and exposed to the moderate ventilation rate was characterized by higher protein and casein content in the fresh cheese and by a greater proteolysis after 90 d of ripening.