Essential oil in vapor phase in combination with Enterococcus mundtii STw38 to improve refrigerated hake fillets shelf-life

Abstract

Essential oils (EOs) in vapor phase were applied together with the bacteriocinogenic strain E. mundtii STw38 to improve the shelf life of Argentinean hake -Merluccius hubbsi-. Evaluated EOs were oregano, thyme, rosemary, and lemongrass. In vitro results demonstrated their effectiveness against foodborne pathogen surrogate Listeria innocua, as well as against Lactobacillus plantarum, Shewanella putrefaciens, and fish indigenous biota. The most effective were oregano and lemongrass, showing the lowest minimal inhibitory concentration, and synergic activity when combined against L. innocua and S. putrefaciens. Furthermore, synergic mixtures promoted changes in target microorganisms cell wall. The composition of the volatile phase of a synergic EOs mixture showed a higher presence of oregano components. When applying the EOs alone in hake fillets, total bacteria count increased 3.3 log cycles whereas in the control system the increase was higher than 5 log cycles, and consumers evaluated similarly in taste and smell both the control and the EOs synergic mixtures. When adding the most concentrated synergic mixture (0.147 μL lemongrass/mL headspace and 0.195 μL oregano/mL headspace) together with the bioprotective culture, in 7 days total bacteria count only increased 3 log cycles, showing the effectiveness of the use of EOs together with E. mundtii STw38.