| Different microorganisms have different requirements and tolerances for oxygen,and the acetic acid fermentation process of traditional Chinese cereal vinegar is completed by aerobic microorganisms such as acetic acid bacteria,mold and bacillus,aerotolerant anaerobe such as lactic acid bacteria,and anaerobic microbes such as yeast,and other microbes participate,so the oxygen content will affect the microbial community structure,succession laws and functions in the Cupei of acetic acid fermentation process.However,it is still unclear how the oxygen content of Cupei of acetic acid fermentation changes,and how the different oxygen content affects the microbial community structure and function of acetic acid fermentation process.This study is of great significance for understanding the fermentation mechanism of Chinese traditional cereal vinegar,improving the production process of vinegar,and improving the flavor quality of products.In this study,a stable vinegar acetic acid fermentation model and the method of oxygen dection was first established in a laboratory with a small tank.The succession law of microbial community structure of the different spatial location?top and bottom layers?Cupei was analyzed using high-throughput sequencing technology.Then the effect of oxygen content on the microbial community structure and function of vinegar brewing was investigated through regulate the frequencies and methods of turnning over Pei.Finally,the species composition of lactic acid bacteria and acetic acid bacteria were optimized and combined with stages oxygen control strategy,established a brewing process of multi-strain liquid fermented rice vinegar,which effectively improves the flavor quality of liquid fermented rice vinegar.The main results of this study are as follows:?1?Four batches of acetic acid fermentation were carried out using a small test model.During the acetic acid fermentation process,the total acidity of the Cupei increased from about 1.00 g·100g-1 Pei to about 4.50 g·100g-1 Pei.The temperature increased from 20 to 25?on day 0 to about 45?at the peak,at the end of the acetic acid fermentation it drops below30?,the moisture fluctuates between 60 to 70%,the pH of the leaching solution drops from4.40 to about 3.80,and the reducing sugar decreases from 2.00 g·100g-1 Pei to 1.00 g·100g-1Pei.The research results show that the fermentation batch of laboratory vinegar model has good stability.?2?The oxygen content in Cupei is about 200?mol·L-1 at the start of acetic acid fermentation and after the turnning over Pei.As the acetic acid fermentation,the oxygen content in the Cupei decreases gradually,and the oxygen content in the bottom layer Cupei decreases to 0 at about 10 h,and then it is in an anaerobic state until 60 h,each turnning over Pei can be effective increasing the oxygen content in Cupei,the rate and rate of decrease of vinegar oxygen content at the end of acetic acid fermentation are both reduced.The oxygen content of the top layer Cupei fluctuates around 100 to 200?mol·L-1.On day 0 of acetic acid fermentation,the high-abundance bacteria in Cupei are mainly Lactobacillus,Acetobacter,Pantoea,Agrobacterium,Pseudomonas,Sphingomonas and Xanthomnas.The relative abundance of Acetobacter increased first and then decreased,and the relative abundance of Lactobacillus first decreased and then increased.The relative abundance of other bacteria gradually decreased with the acetic acid fermentation.On the 0th day of acetic acid fermentation,the high-abundance fungi in vinegar were Fusarium,Alternaria and Epicoccum.The relative abundance of Fusarium and Alternaria decreased during the acetic acid fermentation,while the relative abundance of Epicoccum remained basically unchanged.The relative abundances of fungi such as Cladosporium,Cryptococcus,Septoriella,and Aspergillus are very low in vinegar on day 0,but as the acetic acid fermentation,their relative abundances increase significantly.?3?Through the control of different frequency and methods of turning over Pei,it was found that the temperature of group H?2 times/day,overall turning?,group M?1 times/day,overall turning?,group L?0.5 times/day,overall turning?and group ZAV?2 times/day,layer by layer?fluctuates between 25 to 45°C,and the oxygen content fluctuates between 0and 210?mol·L-1,but there is a difference in the changing rules.The total acid and acetic acid concentrations of the top and bottom layer Cupei in groups H,M and ZAV and the bottom layer Cupei of group L have been increasing as a whole,while the total acid and acetic acid concentrations in the top layer Cupei of Group L have first increased and then decreased.The lactic acid content of the top layer Cupei in the four groups showed an overall downward trend,while the lactic acid concentration in the bottom layer Cupei in the group H,M,and ZAV did not change much,and the bottom layer Cupei in the group L showed an overall upward trend.At the end of acetic acid fermentation,the total acidity of group H and group L is about 5.50 g·100g-1 Pei,and the group M and group ZAV is about 6.00 g·100g-1 Pei.The lactic acid content of Cupei at the end of acetic acid fermentation decreased with the increase of turn over Pei frequency.ZAV group was closer to M group.On day 0,the main bacteria in the top layer Cupei are Lactobacillus,Acetobacer,Xanthomnas,Agrobacterium,and Sphingomonas,but there is no Acetobacer in the bottom layer Cupei;by day 5,the most important bacteria in the top and bottom layer Cupei are all changed to Lactobacillus,Acetobacer and Gluconacetobacer.The results of the study show that oxygen content first affects the metabolism of microorganisms and the metabolic products of microorganisms in turn affect the community structure of microorganisms.?4?Select 10 strains of lactic acid bacteria anaerobic fermented bran leachate,and then mix with alcohol mash and inoculate acetic acid bacteria for aerobic fermentation to brew liquid fermented rice vinegar.It was found that the total acid of the Lactobacillus reuteri L-05group reached the highest on the 7th day,and sensory evaluation score is the highest.The Lactobacillus brevis L-02 group has the most types of volatile flavors--37 kinds,and the Lactobacillus buchneri L-01 group has the highest total concentration of volatile flavors--1267?g·L-1.The results show that inoculation of lactic acid bacteria combined with a staged oxygen control strategy may have the potential to shorten the fermentation cycle and improve the flavor quality of liquid fermented rice vinegar. |
PDF Full Text Request