Changes Of Biogenic Amines In Cowpea Pickles Produced By Multi Round Fermentation And Characteristics Of Biogenic Amines Production By Strains

Pickles has unique flavor,rich nutrition and other characteristics,but the biogenic amines(BAs)pollution may exist in the production process of pickles,leading to food safety hazards.In this study,to fully grasp the variation character of BAs during the fermentation process of pickles and improve the food safety of traditional pickles,cowpea was used as raw material,production methods of natural fermentation and brine inoculation fermentation were used to carry out continuous multiple rounds of fermentation.The BAs content and related physical and chemical properties were measured and analyzed,and the strains producing BAs in pickles were screened by selecting culture media combined with HPLC,identified by molecular biology techniques.The characteristics of BAs produced by strains with high BAs content under different environmental conditions were explored.The main research findings are as follows:1.The analysis and detection results of organic acids,free amino acids,BAs and other physical and chemical components in two kinds of pickles show that: the total acid content continuously accumulates with fermentation at the end of each fermentation cycle,and brine fermented pickle(BFP)is higher than natural fermented pickle(NFP),the nitrite content was lower than 5 mg/kg,and the number of microorganisms in NFP was higher than BFP.Four kinds of organic acids were detected by HPLC,including oxalic acid,tartaric acid,lactic acid and citric acid,the content of lactic acid was the highest.Fifteen free amino acids were detected by automatic amino acid analyzer.Threonine,serine,glycine,isoleucine and lysine were the five highest amino acids in pickles.BFP’s free amino acid content was higher than NFP.Four kinds of BAs were detected by HPLC,including tryptamine,putrescine,histamine and spermidine.The content of putrescine and histamine was the highest.The BAs average content of BFP was 224.45 mg/kg,much higher than 91.46 mg/kg of NFP.The content of histamine in NFP gradually decreased with fermentation,while BFP showed the opposite trend.The content of NFP biogenic amines increased first and then decreased with fermentation,while the content of BFP biogenic amines was relatively stable,fluctuating between 206.92 and 244.61 mg/kg.Pearson correlation analysis showed that there was a significant negative correlation between histamine content and organic acid content in the two pickles,but there was no significant correlation between histamine content and free amino acid content.2.A total of 26 strains with the ability to produce BAs were screened from the fermentation process of pickles,and identified by 16 S r RNA technology as 10 strains of Enterobacter sp.,4 strains of Klebsiella sp.,2 strains of Leclercia sp.,2 strains of Leriotia sp.,1 strain of Pseudocitrobacter sp.,1 strain of Pantea sp.,5 strains of Weissella sp,1strain of Lactobacillus sp.Quantitative analysis by HPLC found that the production of BAs of lactic acid bacteria was very low,while other strains of enterobacteriaceae had strong ability to produce BAs,and the total production of BAs was much higher than 1000 mg/L.Putrescine and cadaverine were the main types of BAs-producing bacteria,which also confirmed that microbial production of BAs has strain specificity.3.In order to explore the effect of different environmental conditions on the ability of BAs-producing strains to produce BAs,five BAs-producing strains(C3,C6,C7,C16,C19)with different characteristics of BAs-producing strains were selected and cultured in 0.5%amino acid broth at different p H(3.5,4.5,5.5,6.5),different salinity(2%,4%,6%,8%)and different temperature(10℃,20℃,28℃,37℃)for 48 hours,and the content of BAs in the culture solution was determined.The results showed that p H value and salinity could significantly affect the content of BAs-producing strains,and the ability of BAs-producing strains was relatively less affected by temperature.When p H was lower than 3.5 or salinity was increased to 8%,most strains could hardly produce BAs.In summary,cowpea pickles has a high content of BAs during multiple rounds of fermentation,with an average content of more than 100 mg/kg,and BFP is higher than NFP.Enterobacteriaceae strains are microorganisms with strong BAs production capacity in pickles.Adjusting the culture environment can significantly affect their BAs production capacity,p H and salinity have the most obvious effects.Therefore,this study deepened the understanding of BAs in the traditional fermentation process of pickles,and provided a theoretical reference for the control of BAs in pickles.