Driving Factors Of Acid Production By Acetobacter Pasteurium

There are some problems in high acid vinegar fermentation,such as low utilization rate of substrate,insufficient acid production and poor flavor.Nitrogen sources promote the synthesis of cellular substances and nitrogen-containing metabolites.In addition,the acid alcohol in production causes stress to vinegar fermentation.Therefore,this study selected Acetobacter pasteurium from vinegar as the research object,and analyzed its acid production and physiological characteristics under different nitrogen sources and acid and alcohol stress factors.Finally,the quality of vinegar was improved by means of good strain and nutrient salt.(1)High-acid strain was screened out and identified as Acetobacter pasteurium.The acid production of the strain was measured under different nitrogen sources.The results showed that the acid production was 8.8 ～ 34.5 g/L,and the acid production in the YE group was higher than that in the peptone group.The effects of 10 amino acids on acid production were verified.The results showed that when alanine and arginine were absent,they were 62.5% and 60% lower than the blank group,respectively.The absence of proline was 27.1% higher than that of blank group.(2)The growth and acid production of strains under different acid and alcohol stress factors were measured.Ethanol increased from 4%(v/v)to 14%(v/v),and the growth amount of strain decreased gradually.Under the stress of 12%(v/v)ethanol or 8%(v/v)ethanol plus 1%(v/v)acetic acid,the highest acid yield was 67.8 g/L and 66 g/L.(3)Physiological characteristics of the strain were determined by scanning electron microscopy,cell membrane fluidity and enzyme activity.The results showed that when the acid and alcohol stress was low or the nutrient condition was good,the bacteria cells were easy to senescence and deformation.When acid and alcohol stress is high or nutrient condition is poor,the cells of bacteria are easily damaged and deformed.High ethanol concentration or low acid stress can increase cell membrane fluidity.When the ethanol concentration increased from 4%(v/v)to 12%(v/v),the enzyme activity first increased and then decreased.1%(v/v)acid stress also increased the enzyme activity of the strain.(4)The volatile flavor substances of liquid fermented rice vinegar strengthened by strain and nutrient salt were detected.The results showed that group C(blank)contained 13 kinds of volatile flavor substances,group A(strain enhanced group),group S(nutrient salt enhanced group)and group A+S(strain plus nutrient salt enhanced group)contained 21 kinds of volatile flavor substances,24 kinds of volatile flavor substances and 23 kinds of volatile flavor substances,respectively.Among them,the esters in A+S group were the most abundant.The experimental group all contained high content of acetic acid and acetoin(3-hydroxy-2-butanone).Groups S and A+S are rich in iso-valeric acid.group A and group A+S contained prominent 2-phenylethanol.groups A and S contained higher levels of n-nonaldehyde.In addition,the color of groups A and C was light yellow,and that of groups S and A+S was amber.groups A,S and A+S make liquid fermented vinegar more sour,sweet,soft and mellow.