Efect of season and geographic area on the composition of fatty acids in cow milk

Abstract

A study of the fatty acid composition of milk fat, and of its variation due to geographical and seasonal effects is necessary to better understand rheological properties of milk fat (melting, spreadability, hardness), to facilitate detection of possible adulterations, and to give more information regarding the levels of butyric acid and conjugated linoleic acid C18:2, due to their nutritional importance.
Milk samples were collected on a monthly basis during one year (from June 1998 to May 1999) at tank level in six dairy plants of the VIII^th, IX^th and X^th regions. Fatty acids from cow’s milk were analysed as methylesters using gas-liquid chromatography. As sampling was done at tank level of dairy plants, emphasis was placed on seasonal and regional variations. For the analysis of seasonal and regional variations, the quantified fatty acids were classified according to their chain length: short chain (C4 – C10), intermediate chain (C12 – C16) and long chain (C18 – C18:2 conjugated).
An effect of season was observed only in the case of short chain fatty acids, with an average value significantly (p < 0.05) lower in summer than in spring. Analysis with geographic area revealed significant differences (p < 0,05) for all fatty acids. The average values for the content of short chain fatty acids in milk from the IX^th region were significantly (p < 0,05) lower (8,24 %) than those in milk from the VIII^th and X^th regions; the intermediate chain fatty acids had an average value significantly (p < 0,05) higher (42,9 %) in milk from the VIII^th region than those found in milk from the IX^th and X^th regions; in contrast the long chain fatty acids within milk from the VIII^th region had a significantly (p < 0,05) lower value than those found in milk from the IX^th and X^th region.
Conjugated linoleic acid, which has been shown to inhibit carcinogenesis in test animals, was found in significantly (p < 0,05) higher concentration in samples from the IX^th region, with an average value of 1,75 % in comparison with an average of 1,41 % in milk from the VIII^th region. At seasonal level, the highest value was found during the spring-summer period (1,75 %), while for the autumn-winter period the values (1,59 %) were lower.
The factors of season and geographic area cause significant differences in the composition of fatty acids in cow milk fat.