Evaluation of volatile compounds and free fatty acids in set types yogurts made of ewes', goats' milk and their mixture using two different commercial starter cultures during refrigerated storage.

Six different types of yogurt were manufactured from Damascus goat milk, Awassi ewe milk and a mixture of equal portions of the 2 species of milk using 2 types of commercial yogurt cultures (CH-1 and YF-3331). Yogurts were chemically analysed at 1, 7, 14 and 21days of storage. Results showed that cultures significantly affected acetaldehyde (P<0.05), acetone (P<0.05) and diacetyl (P<0.001) contents. Type of milk significantly influenced acetaldehyde (P<0.05), diacetyl (P<0.001), acetoin (P<0.001) and ethanol (P<0.05) levels. Significant variations occurred in acetaldehyde (P<0.001) and acetoin (P<0.05) contents during the storage. Short-chain free fatty acids were the highest in ewes' milk yogurt made with culture YF-3331, and increased during storage, while the levels of medium-chain free fatty acids, except for decanoic acid, were unchanged and the amount of long-chain free fatty acids decreased during storage. Cultures used and types of milk had no effect on long-chain free fatty acids in yogurts.