Abstract: The effect of different concentrations of garlic essential oil on putrescine accumulation by Lactobacillus delbrueckii isolated from smoked horse meat sausages were explored, and the underlying mechanism was elucidated. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to analyze the gene expression of agmatine deiminase in Lactobacillus delbrueckii when cultured in the presence of different concentrations of garlic essential oil. Ultra performance liquid chromatography was used to monitor putrescine produced by the pure culture of Lactobacillus delbrueckii for 48 h. Additionally, the strain was incubated into smoked horse meat sausages with different concentrations of garlic essential oil and cultured for 28 days. Samples were collected during the fermentation period to measure the total number of bacteria, pH, and putrescine accumulation. Results showed that for both culture modes, garlic essential oil could significantly inhibit bacterial growth. It significantly inhibited the decrease in pH in the pure culture, but had little effect on the final pH of smoked horsemeat sausages. Garlic essential oil had little impact on the transcription of the regulatory gene aguR, but significantly inhibited the transcription of the operon aguBDAC (P < 0.01). Increasing garlic essential oil concentration can significantly reduce the generation of putrescine both in pure culture and during the fermentation process of smoked horse meat sausages.

Key words: garlic essential oil, Lactobacillus delbrueckii, putrescine, bacteriostasis, agmatine deiminase, gene expression