Effect of pasteurization and season on milk composition and ripening of Ras cheese

摘要

The objective of this study was to compare between the raw and pasteurized Ras cheese from cow's milk through the season. The chemical composition of cheese was also demonstrated as the ripening period progressed. High solids in winter milk and low solids in summer milk were observed and were attributed to the hot weather and the poorer quality pastures. Casein as a percentage of true protein and the casein to fat ratio were higher in spring and summer milk. Fat in the cheese made from winter milk was higher and the total protein was lower than that in spring and summer cheeses. The chemical changes during ripening period of six months were examined for composition, flavour intensity, acidity, pH, soluble protein and total volatile fatty acids. Raw or pasteurized cheese in each period of winter, spring and summer were evaluated for flavour, body and texture and appearance at the end of ripening. Fat and protein recovery in the cheese were not affected by season. Cheese yield from winter milk was higher than from spring and summer milk and was a result of the higher casein and fat in the milk. Raw milk cheese in winter and spring scored higher values for flavour compared to summer cheese. There was a close relationship between the good flavour and the high total volatile fatty acid. Milder flavour was associated with moderate soluble protein and low volatile fatty acid. On the other hand, pasteurized milk cheese in winter, spring and summer with adding yoghurt starter had a more compact body and smoother texture and more holes and cracks. In general, Ras cheese made from pasteurized milk achieved higher score in body and texture and lower score in flavour in comparison to Ras cheese made from raw milk through the season.