Temperature Dependent Antimicrobial Activity of Menhaden Fish Oil in vitro and on Pet Food Kibbles Against Salmonella spp.

Abstract

Fish oil inclusion into a dry pet food provides a source of long-chain omega-3 fatty acids. Polyunsaturated fatty acids (PUFA) in fish oil have antibacterial activity against various foodborne pathogens such as Salmonella and pathogenic Escherichia coli. The purpose of this study was to determine the effect of temperature applied to dry pet food kibbles on the antimicrobial activity of Menhaden fish oil against Salmonella spp. Sterile Menhaden oil was inoculated with ~8 logs of Salmonella cocktail (~3 % moisture; S. Enteritidis , Heidelberg, and Typhimurium) and incubated at 25°C, 37°C, and 45°C. Microbiological evaluation of the water phase was done after 2h on TSA agar. Sterile kibbles were coated with fish oil (7.0 % w/w). Canola oil coating was kept as a control. One hour after coating, the kibbles were inoculated with ~9 logs of Salmonella and incubated at their respective temperature. The microbiological evaluation was conducted at 0h, 2h, 6h, 12h, and 24h. The oil phase of the fish oil system was negative for Salmonella after 2h of incubation and confirmed by enrichment and PCR. From the water phase, 8.1 and 7.3 logs were recovered at 25°C and 37°C respectively and no Salmonella was detected at 45°C. On the kibble, Menhaden oil had higher antimicrobial ( p ≤ 0.05) activity after 12h at 25°C, and throughout the experiment at 37°C. At 45°C, the fish oil had a superior antimicrobial activity against Salmonella cocktail after 2h. When the fish oil alone was compared at different temperatures a higher antimicrobial activity was observed at 37°C and 45°C across all time points. The results indicate antimicrobial activity of the Menhaden oil increases with temperature. This is an important finding to the pet food industry; wherein a higher fat holding temperature (~ 45ºC) and the application process may help mitigate Salmonella on extruded kibbles.