Seasonal variation in conjugated linoleic acid and vaccenic acid in milk fat of sheep and its transfer to cheese and ricotta

The seasonal variation in conjugated linoleic acid (CLA) and vaccenic acid (VA) concentrations in sheep dairy products and the extent of their transfer from milk fat to cheese and ricotta fat were investigated. Samples were collected from two sheep milk processing plants located in North Sardinia (Italy) every two weeks from March through June. Concentrations of fatty acids (FA) in fresh cheese and ricotta fat were primarily dependent on the fatty acid content of the unprocessed raw milk. The content of c9,t11 CLA averaged 1.73, 1.69 and 1.75 mg/100 mg FA methyl esters (FAME), respectively for milk, cheese and ricotta, and differed significantly between cheese and ricotta. The content of VA averaged 3.40, 3.33 and 3.43 mg/100 mg FAME, respectively for milk, cheese and ricotta. The FA composition of dairy products was markedly affected by period of sampling: the mean c9,t11 CLA and VA concentration decreased from March (2.20 and 4.52 mg/100 mg FAME) to June (1.14 and 1.76 mg/100 mg FAME) in all dairy products. No differences in c9,t11 CLA and VA concentration of dairy products were observed between the two dairy companies obtaining milk from the same geographical origin. The seasonal changes in CLA and VA in milk fat were probably related to changes in pasture quality.