This study investigated the effects of cinnamaldehyde on putrescine production by Obesumbacterium proteus in pure cultures and Xinjiang sausage. Scanning electron microscopy was used to analyze the cell morphology of the test bacteria, and reverse transcription real-time fluorescence quantitative polymerase chain reaction was employed to analyze the gene expression of arginine decarboxylase and ornithine decarboxylase of the test bacteria at different cinnamaldehyde concentrations. Single-molecule real-time sequencing was utilized to identify the species composition of the sausage. Moreover, relevant parameters such as putrescine accumulation and microbial growth were evaluated. The results indicated that cinnamaldehyde inhibited the growth of O. proteus by leaking its contents and changing membrane permeability, and significantly reducing putrescine accumulation by inhibiting the expression of arginine decarboxylase (adiA) and ornithine decarboxylase (speF) genes. The cinnamaldehyde concentration revealed an inverse relationship between gene expression and putrescine accumulation. Besides, cinnamaldehyde significantly reduced the abundance of harmful bacteria (Enterobacteriaceae and Pseudomonas), alleviate putrescine content and stimulate the release of amino acids in the sausage. Therefore, adding cinnamaldehyde is an effective method to inhibit putrescine accumulation and reduce the growth of spoilage microorganisms in the sausage.

This study aimed to prepare an inclusion complex ferulic acid (FA) with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and evaluate its effects on the pH, growth, gene expression, and tyramine accumulation in the cultured broth of Enterobacter cloacae L63 and tyramine accumulation in smoked horsemeat sausage inoculated with this strain. Real timequantitative polymerase chain reaction (qPCR) was used to measure the expression of the tyrosine decarboxylase (tdcA), tyrosine/tyramine antiporter (tyrP), tyrosine t-RNA synthetases (tyrS) and Na⁺/H⁺ antiporter (nhaC) genes in the tyramineproducing pathway. In addition, high performance liquid chromatography (HPLC) was employed to detect tyramine accumulation during 48 h of culture of Enterobacter cloacae L63. The results showed that FA and its inclusion complex with HP-β-CD reduced the expression of tdcA and tyrP (P < 0.05), had a strong antibacterial activity against E. cloacae L63, inhibited the increase in the pH of the cultured broth and smoked horsemeat sausage and reduced tyramine accumulation. The inclusion complex was more effective against tyramine accumulation (P < 0.05).

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.