| With the continuous development of vinegar industry,liquid fermentation has become an important method for fermented vinegar.The growth of certain microorganisms or regulate the synthesis of microbial metabolites can be promoted by using low intensity alternating magnetic field to assist rice vinegar for liquid fermentation.So,the acetic acid fermentation of rice vinegar under the action of a magnetic field and the influence of the magnetic field on the growth of acetic acid bacteria and acid production by fermentation was studied.The research will lay a foundation for increasing the output of rice vinegar,reducing production costs,and provide a reference for applying magnetic fields to the production of other kinds of liquid vinegar.In this paper,raw rice was used as raw material.Firstly,the effects of fermentation time,fermentation temperature,yeast addition amount and starter inoculation amount on ethanol production by fermentation of raw rice were studied,and the ethanol fermentation process of rice vinegar was further optimized.Secondly,the low intensity alternating magnetic field was used to assist the acetic acid liquid fermentation of rice vinegar.The effects of magnetic field conditions on the biomass and acid production of acetic acid bacteria were explored,and the kinetic model of acetic acid liquid fermentation under low intensity alternating magnetic field was established.Finally,the transcriptome of acetic acid bacteria during acetic acid fermentation assisted by low intensity alternating magnetic field was studied to explore the mechanism of low intensity alternating magnetic field regulating acetic acid liquid fermentation.The main research conclusions are as follows:(1)The alcohol fermentation of rice vinegar was carried out by semi-solid fermentation.Firstly,the effects of fermentation time,fermentation temperature,yeast addition and koji inoculation on the alcohol production of raw rice were studied by single factor experiment.Then,according to the principle of response surface BBD test design,the alcohol content was used as the response value.The optimal process conditions of semi-solid alcohol fermentation of raw rice were as follows: fermentation time 8 d,fermentation temperature 27?,yeast addition 0.15% and koji inoculation 13.95%.The volatile compounds of rice wine fermented in semi-solid state were analyzed by headspace solid phase microextraction(HS-SPME)combined with GC-MS.A total of 22 flavor compounds were identified,including 8 alcohols,7 esters,2 aldehydes,2 ketones and3 others.(2)Taking the residual sugar content,acetic acid content and acetic acid bacteria biomass as indexes,the conditions of low intensity alternating magnetic field assisted acetic acid liquid fermentation were studied by single factor experiment method.The conditions of magnetic field were determined as follows: magnetic induction intensity was 30 Gs,low intensity alternating magnetic field treatment time was 3 h,and the initial intervention time of magnetic field was 9 h after inoculation.The acid production increased by 44.18 %.The kinetic model of acetic acid fermentation under the optimal conditions of low intensity alternating magnetic field was established,including the Monod kinetic model of acetic acid bacteria growth,the kinetic model of viscous fermentation broth,the kinetic model of substrate inhibition growth and the kinetic model of product inhibition growth.The model constructed by the fermentation kinetics reached a significant level,which can predict the dynamic changes of acetic acid liquid fermentation process of rice vinegar assisted by low intensity alternating magnetic field.(3)The transcriptome of acetic acid bacteria under normal acetic acid liquid fermentation and low-intensity alternating magnetic field-assisted acetic acid liquid fermentation were comparatively studied by transcriptome method.The sequencing results were stable in quality,the repeatability of samples in the group was good and the difference was low,and the gene expression patterns were similar.In addition,266 differential genes were obtained,including 103 up-regulated genes and 163 down-regulated genes.GO enrichment analysis was performed on the differential genes,and the differential genes cya A,cyo C,ZMO1681,cya B and cor A closely related to the biomass,total acid product synthesis and substrate alcohol consumption of acetic acid bacteria were found.It was found that the respiratory reductase activity encoded by cya A and cyo C genes was increased by applying low-intensity alternating magnetic field,which promoted the growth of acetic acid bacteria.The application of low-intensity alternating magnetic field also accelerated the transport of ions and other substances mediated by the transmembrane transporters encoded by ZMO1681 gene,cya B gene and cor A transporter encoded by cor A gene,strengthened the stability of biofilm and improved the catalytic oxidation reaction rate.After KEGG pathway analysis,the ribosomal pathway(ko03010)involved in the metabolic pathways related to acetic acid bacteria cell growth;the metabolic pathways of alanine,aspartic acid and glutamate(ko00250)and oxidized phosphoric acid involved in the metabolic pathways related to the acetic acid bacteria biofilm Pathway(ko00190);quorum sensing of acetic acid bacteria,thiamine metabolism,and terpenoid and polyketide metabolism,which are involved in acetic acid bacteria stress response related metabolic pathways.The differential gene expression was up-regulated after applying low-intensity alternating magnetic field,which affected the biomass,metabolism and biosynthesis of acetic acid bacteria,and promoted a series of biochemical reactions of acetic acid bacteria. |
PDF Full Text Request