Effect of fatty acids in goats' milk on the response of microbial inhibitor tests

Autores UPV
CONGRESO Effect of fatty acids in goats' milk on the response of microbial inhibitor tests


The goal of this study was to evaluate the inhibitory effect of different fatty acids on the response of microbiological inhibitor methods for the detection of antibiotics in goats¿ milk. Milk from four individual goats not treated with antibiotics the last months was commingled to be used as ¿blank milk¿. A 0.15% (w/v) of the following fatty acids: butyric, capric, caproic, caprylic, elaidic, lauric, linoleic, α-linolenic, myristic, oleic, palmitic, palmitoleic, stearic and vaccenic acid was added to blank goat milk. The milk samples were analysed in triplicate by various microbial inhibitor tests (BR-AS Special, CMT-Copan Milk Test, Delvotest SP-NT, Delvotest T, Brilliant Black Reduction Test MRL, Charm Blue Yellow II, CowSide II, Eclipse 100 and Eclipse 3G) to determine the false positive rate of results. All positive milk samples were also analysed after application of a heat treatment (10 min at 80°C) to try to reduce or to eliminate the interference by fatty acids on the tests. It was observed that the fatty acids caproic (3 out of 9 tests), caprylic (6 out of 9 tests), capric (all 9 tests), lauric (5 out of 9 tests), myristic (1 out of 9 tests), palmitoleic (4 out of 9 tests) and α-linolenic acid (5 out of 9 tests) were causing positive results in one or more tests. Delvotest SP-NT and CMT were only affected by capric acid and where hence the most robust tests. In general, the heat treatment did not improve the robustness of microbial methods; only negative results were obtained for caproic and myristic acid after heat treatment for Eclipse 3G and CowSide II, respectively.