UC Davis

Organic bovine milk in the U.S. is considered and labeled differently from conventional bovine milk because of the regulations and certification by the USDA. These regulations by the USDA for organic bovine milk in the U.S. are claimed to change the fatty acid profile of organic milk and increase levels of n-3 fatty acids. This study investigated differences in fatty acid profiles between 12 organic and 12 conventional retail bovine milk brands in California to test the hypothesis that organic milk will contain more n-3 fatty acids. The milk samples were collected from U.S. retail stores in California, once each in the early late Winter of March in 2020 and late Summer of August in 2020 to account for seasonal variations of the fatty acid profiles between organic and conventional milk. Milk samples from dairy farms in California were selected to consider regional variations. Milk fatty acids were identified and their levels in each sample measured through a GC-FID. Two Sample T-Test showed that levels of caprylic, myristic, myristoleic, and α-linolenic acid (ALA) were significantly (P<0.05) greater in organic retail milk (OM) than conventional retail milk (CM) and levels of linoleic (LA) and stearic acid were significantly greater in CM than OM in both Winter and Summer. ANOVA Single Factor with Tukey HSD Test resulted in levels of myristic, myristoleic, and ALA to be significantly greater in OM than CM and levels of LA to be significantly greater in CM than OM. OM demonstrated no significant differences (P>0.05) in levels of any of the 13 identified fatty acids between Summer and Winter samples through T-Test and ANOVA Single Factor with Tukey HSD Tests. CM demonstrated significant differences, through T-Tests, in levels of fatty acids capric, lauric, myristic, oleic/elaidic, and LA between Winter and Summer samples. ANOVA Single Factor with Tukey HSD Test on CM resulted in no significant differences in levels of any of the fatty acids between Winter and Summer samples. Through performing linear discriminant analysis, we were able to accurately authenticate organic and conventional retail milk samples using their fatty acid profiles with an accuracy of 95.83% without considering seasons, Winter and Summer. The accuracy of the linear discriminant analysis dropped to 83.33% when having to also authenticate organic and conventional retail milk samples in their respective Winter and Summer sample groups. Overall, this thesis demonstrates significantly greater ALA in organic retail milk than conventional retail milk in California.