Effect of Coreopsis tinctoria Essential Oil on Tyramine Production and Related Gene Expression in Enterococcus hirae

The aim of this study was to investigate the effect of different concentrations of Coreopsis tinctoria essential oil on tyramine production by Enterococcus hirae N47. Reverse transcription quantitative real-time polymerase chain reaction (real-time PCR) was used to analyze the expression of the genes involved in the tyrosine decarboxylase (TDC) pathway in E. hirae treated with C. tinctoria essential oil. High performance liquid chromatography (HPLC) was used to detect tyramine. The changes in pH, total viable count and tyramine accumulation in smoked horse sausage with different concentrations of C. tinctoria essential oil inoculated with E. hirae were evaluated during the 28-day fermentation period. The results showed that for both the pure culture of E. hirae and smoked horse sausage, C. tinctoria essential oil significantly reduced tyramine accumulation by inhibiting the growth of microorganisms and the expression of the tyr DC and tyr P genes in the tyrosine decarboxylation pathway (P < 0.05). Tyramine contents in smoked horse sausage with C. tinctoria essential oil at the minimal inhibitory concentration (MIC) and 1/2 MIC were 78.52 and 45.83 mg/kg, respectively, which were 64.72% and 79.41% lower than that in the control group (not added with C. tinctoria essential oil, inoculated with E. hirae), respectively.