Survey of Retail Milk: Comparison of the Fatty Acid Composition of Conventional Milk and Milk Labeled as 'rbST-Free' and 'Organic'

摘要

In recent years, milk selection in retail stores has expanded. Conventional, rbST-free and organic labeled milk are characterized by different management practices. The fatty acid composition of milk can be modified by manipulating the cow's diet; however it is unclear whether the milk labeling differences in cow management affect the composition of milk fat. The objective of the present study was to compare the fatty acid composition of conventional milk with that labeled as rbST-free or organic. A total of 296 samples were collected in blocks containing conventional, rbST-free and organic milk from retail stores in the 48 contiguous states. Fatty acids were extracted, methylated, and gas chromatography was used to quantify individual fatty acids. Conventional and milk labeled as rbST-free showed no differences in fatty acid composition. Organically labeled milk was similar, with minor statistical differences from conventional and rbST-free milk. These differences included greater levels of trans-11 18:1 (vaccenic acid; VA), cis-9, trans-11 C18:2 (rumenic acid; RA), as well as greater total saturated fatty acids, lower monounsaturated fatty acids and lower total trans fatty acids. The variation in RA and VA in organic milk was greater as compared to the variation observed for conventional and rbST-free milk samples. Overall, some differences were significant in organic milk fatty acid composition, but these were minor and quantitatively of no biological importance in comparing conventional, rbST-free and organic milk.