Screening Of Lactic Acid Bacteria Starters From "Yucha" And Evaluation Of Their Application

“Yucha”is fermented with fish and rice in anaerobic condition under room temperature.In order to improve the quality of“Yucha”and speed up the fermentation process,this project studied the quality and microbial community structure of spontaneously fermented“Yucha”at different temperatures,and screened strains suitable for fermented“Yucha”as starters to inoculated fermentation.Effect of starters on quality and microbial distribution in inoculated“Yucha”were also studied.The detailed results were as follows??1?At different fermentation temperatures?15°C,20°C,25°C and 30°C?,the hardness and elasticity of the fish in each group showed a decreasing trend.The recovery and chewiness rose at 7 d and then decreased.The fish had the best texture at 20°C.The higher temperature,the more lactic acid in“Yucha”.The pH values of all samples were below 4.5 at 7 d,and then maintained 3.7-4.1.The predominant microbes of each group were established from the third week of fermentation.Redundancy analysis results showed that temperature was the most significant factor on the bacterial distribution.The dominant strains of fermented“Yucha”were Lactobacillus sakei and Lactobacillus plantarum at 15°C,while the dominant strain was L.plantarum at 20°C and 25°C;the dominant strain was the Lactobacillus brevis at 30°C.?2?Lacotococcus lactis?Ll?,L.sakei?Ls?,Enterococcus avium?Ea?and L.plantarum strains1-6?Lp1-6?were isolated and identified from spontaneously fermented“Yucha”,then their salt tolerance,acid resistance,bile salt resistance and antibacterial properties were evaluated.Lp1,Lp3,Lp6 reached 20×10⁹ cells/mL after 24 h growth in 6%NaCl environment.The OD_600nm values of Lp1,Lp3,Lp5,Lp6 reached 0.25 after 24 h at pH 3.0.The OD_600nm00nm values of Lp1,Lp5,Lp6 in 0.1 mg/100 mL bile salt were more than 0.7 after 24 h.Lp1,Lp4,Lp5 and Lp6 showed significant inhibition on Staphylococcus aureus and Salmonella.Lp1 and Lp5 have outstanding overall performance and have the potential value of developing an effective starter.?3?Lp1,Lp5 and Ll were inoculated into“Yucha”,and spontaneously fermented“Yucha”was used as a control group,the acid production rate of the inoculated groups were faster,indicating that inoculated fermentation accelerated the fermentation process.L.plantarum was the dominant strain of the four groups,although the Ll group was inoculated with L.lactis and finally replaced by L.plantarum.The variety and contents of volatile compounds in inoculated groups were more abundant,and enhanced the flavor of“Yucha”.Cluster analysis showed that the flavor profiles of Lp1 and Lp5 groups were similar at the end of fermentation.The volatile compounds profile of L1 group significantly changed during fermentation,and the Hexanal proportion increased from 1.18%to 31.62%at 28 d.From the analysis of volatile compounds interactions,it can be presumed that 1-methylnaphthalene may be used as a detection index for the maturation of“Yucha”.