Effects Of Seasonal Variation On Bacterial Flora And Flavor Substances In The Fermentation Of Baoning Vinegar

Baoning vinegar is one of the four famous vinegars in China.However,due to its process,which adopts the open mixed multi-strain hybrid fermentation mode,so it is more susceptible to external environmental conditions(such as seasons,raw material batches,etc.),and causes the low quality of finished vinegar consistency.In this paper,by collecting samples of vinegar,raw vinegar and cooked vinegar during the fermentation of four seasons of Baoning vinegar,high-throughput sequencing technology combined with the analysis of conventional physical and chemical indicators and organic acids,free amino acids and volatile flavor substances were applied to determine the difference in quality between different batches of seasonal during fermentation and analyse its causes.Hoping to provide theoretical basis and technical support for the continuous production of high quality of Baoning vinegar.The main results are as follows1.By analysing the bacterial flora of starter,feedstock of waste residue and different fermentation stages of Baoning vinegar,the highest abundance was Acetobacter and Lactobacillus.,The differences in bacteria flora structure in the genus level of starter,feedstock of waste residue and fermentation process in different seasons,was mainly manifested the changes of Lactobacillus and Acetobacillus.Before 5 days of fermentation,it was mainly affected by the change of Lactobacillus abundance,and after five days,it was mainly affected by the change of Lactobacillus and Acetobacillus.Because Baoning vinegar is a multilateral fermentation,so saccharification,liquorization and acidification happened at the same time,but different stages had different action intensity.Before 5 days fermentation,was mainly dominated by liquorization,and after 5 days,acidification gradually increased.However,due to the differences in bacterial flora structure,the acidification degree of fermented vinegar in different seasons was different,which led to the differences in vinegar production rate in different seasons.There were some differences in starter,feedstock of waste residue and vinegar in different seasons,but they were not as different as those in the same fermentation season2.Through monitoring the indexes of total acid,reducing sugar,starch,alcohol and water content in the fermentation process of Baoning vinegar,the results showed that the variation trend of fermented total acid in different seasons was consistently,and at the end of fermentation the difference of fermented total acid in different seasons was not significantly,and the fermented total acid in autumn was the highest.Starch utilization in winter was the highest,followed by autumn and spring,and the summer was the worst The change trend of reducing sugar content of spring,summer and autumn in the fermentation cycle were increased first,and then decreased.At the end of fermentation,reducing sugar content was 0.59%in spring,0.96%in summer,and 0.63%in autumn However,the reducing sugar content in winter was reduced before 5 days fermentation,it might be attributed to the fact that the environment of vinegar pei in winter was more conducive to the growth and reproduction of microorganisms,and could increase the acid production by microbial metabolism.During the fermentation process,on the 5th day,the alcohol content in winter,spring,autumn and summer reached maximum was 1.65%,1.75%,1.07%and 0.7%,respectively.During the fermentation of vinegar pei in different seasons,the water content of vinegar pei increased continuously with the increase of fermentation time.However,due to the high temperature in summer and rapid evaporation of water,the water content of vinegar pei was lower than that in other three seasons at the end of fermentation3.By determining the seven organic acids in the sample of Baoning vinegar,the content of lactic acid and acetic acid was the highest,the content of oxalic acid and tartaric acid was lower than the content of lactic acid and acetic acid,and the contents of malic acid,citric acid and succinic acid were not detected.Among the samples in different seasons,lactic acid and acetic acid were the highest organic acids,which were related to the highest abundance of Lactobacillus and Acetobacter during fermentation.In finished vinegar the content of lactic acid and acetic acid was the highest,and the content of lactic acid was higher than acetic acid,which made the taste of Baoning vinegar was much softer The acid content of cooked vinegar samples in different seasons was different.From the perspective of acetic acid content,the quality of spring,autumn and winter was better than that of summer.The content of oxalic acid and tartaric acid was low,and the trends in different seasons were consistently4.The total amino acid content of Baoning vinegar was different in different seasons,which cooked vinegar in autumn(1152.96 mg/100 mL)>spring(1124.13 mg/100 mL)>winter(1036.28 mg/100 mL)>summer(990.42 mg/100 mL).The proportion of essential amino acids in different seasons:summer vinegar(47.89%)>autumn vinegar(45.59%)>spring vinegar(44.83%)>winter vinegar(41.77%);summer cooked vinegar(47.13%)>autumn cooked vinegar(45.32%)>spring cooked vinegar(44.36%)>winter cooked vinegar(42.80%).The difference of bitter amino acid of Baoning vinegar in different seasons was small;only the umami amino acid in winter was higher than the average level 7.21%;the sweet amino acid content in spring was the highest.Compared with the SRC of riped vinegar in different seasons,the score of vinegar in winter was the highest,while the summer was only 50.86,which was lower than the average of 67.59.Therefore,from the perspective of the ratio of essential amino acids,the quality of cooked vinegar in winter was the best,and the quality of cooked vinegar in summer was poor5.There are 42 kinds of volatile flavor substances,which the matching degree was higher than 80%.Among them,there are two kinds of esters,three kinds of acid substances,six kinds of alcohol substances,and four kinds of aldehydes;only 1 kind of ketones and 3 kinds of heterocyclic substances,which were considered as the characteristic flavor substances.Among them,the relative content of furfural was high,and coconut aldehyde,4-ethylguaiacol,decyl acetate and ethyl lactate were the unique flavor substances of Baoning vinegar,which could be used to distinguish Baoning vinegar from other vinegar.