Degradation Mechanism Of Biogenic Amines By Pediococcus Pentosaceus 37X-9 And The Bacterial Diversity Of Traditional Beef Jerky

Beef jerky,as a traditional meat product in China,has a long history of production,unique taste and national characteristics.It has certain potential food safety problems due to it is easy to produce biogenic amines produced by nitrogen compounds metabolism.The accumulation of biogenic amines is also an urgent problem in the meat product industry,as consumers pay more and more attention to the safety of meat product.The bacterial diversity in traditional beef jerky from Inner Mongolia were determined by High-throughput Sequencing,and the correlation of bacterial diversity and biogenic amine content was investigated.Meanwhile,lactic acid bacteria with biological amine degradation and high-yield signaling molecule AI-2 were screened from sausage and jerky.The effects of culture conditions on the physiological characteristics,biogenic amine-lowering capacity,and the Lux S/AI-2 QS system of lactic acid bacteria were examined.The mechanism of lactobacillus on the metabolism of biological amine based on the signaling molecule AI-2 were explored by Proteomics and Metabolomics.These results focuses on providing extensive information on target-mediated specific lactobacillus functions and the safety of traditional meat products.These results were followed:The bacterial diversity of sixteen different kinds of beef jerky samples from different regions of Inner Mongolia was determined and analyzed by high-throughput sequencing technology.The results revealed that the major dominating bacteria phylum in beef jerky were Proteobacteria and Firmicutes,and the dominant bacteria genus were Pseudomonas and Ralstonia.The contents of eight BAs were detected in beef jerky,and the contents of overall BAs were significant difference(308.29～1691.73 mg/kg).The amounts of putrescine were found to be positively correlated with the abundance of unclassified＿f＿Enterobacteriaceae and Staphylococcus,while the contents of phenylethylamine,cadaverine,and tyramine were positively correlated with unclassified＿f＿Enterobacteriaceae,norank＿f＿norank＿o＿Chloroplast and Aeromonas by analyzing the correlation between 33 genera of bacteria and 8 kinds of BAs.The 41 lactic acid bacteria strains were screened from 50 strains which not-producing BAs or low-producing BAs by the microbial color method and high performance liquid chromatography.The degradation ability of lactobacillus to putrescine,tyramine,cadaverine and histamine was tested,found that 36 strains can degrade at least one biogenic amine,the strains 37X-9,30X-5 and X3-4B showed relatively high degradation rates of the putrescine,cadaverine,histamine,and tyramine.The activity of multicopper oxidase with 30X-4,30X-5 and 37X-9 strains were significantly higher than other strains(P<0.05),the activity of signaling molecule AI2 with 37X-9,30X-7 and X3-4B strains was significantly higher than the positive control(P<0.05).The Pediococcus pentosaceus 37X-9 had high degradation ability of biogenic amine and activity of multicopper oxidase(>10 U/L)and signaling molecule AI-2.The signal molecules AI-2 activity and the BAs-degradability of P.pentosaceus37X-9 were inhibited under relatively strong acid conditions(p H 4.5),and the level of MCO(multicopper oxidase)gene transcription was significantly lower than in other groups(P<0.05).The activity of the signaling molecule AI-2 was decreased at 20°C,and the capacity of degrading BAs and the level of MCO gene transcript were significantly lower than in the control group(P<0.05).The MCO gene transcription and signal molecule AI-2 activity were promoted under 1.5% Na Cl stress.The optimal condition for the biogenic amine ability of P.pentosaceus 37X-9 were p H 6.5,temperature 37°C,and without Na Cl.The ability degrading tyramine of P.pentosaceus 37X-9 was significantly improved by the addition of the signaling molecule AI-2(P<0.05),and was maximum at a final concentration of 1700 nmol/L.According to the q PCR results,the expression of the MCO gene was significantly increased(P<0.05)by AI-2,but the AI-2 had no discernible effect on P.pentosaceus 37X-9’s capacity to degrade histamine,cadaverine,and putrescine(P>0.05).The 297 proteins had significantly differential down-regulation and 382 proteins had significantly differential up-regulation by the proteomic sequencing.The 9 proteins,including Mod F,Sec A2,Ddp C,Sec Y,and Fts Y,were significantly up-regulated in the experimental group,and the proteins involving in pyruvate metabolism,ABC transport,and metabolic processes played crucial roles.By using untargeted metabolomics,the total of 539 significantly different metabolites were found which were mostly included amino acids,peptides and analogs,amines,carbohydrates and binders,purine and purine derivatives,etc.Tyramine,spermidine,spermidine,L-tyrosine,and ornithine were all significantly reduced,which indicated that the content of BAs was significantly decreased by the addition of signaling molecules(P<0.05).Correlation analysis between differential proteins and differential metabolites showed that the difference of tyramine reducing ability of P.pentosaceus 37X-9 may be related to ABC transport,and biosynthesis of cofactors.