| Soy sauce is an important daily condiment in our country,which is delicious and nutritious.The types and contents of aroma components are closely related to the quality of soy sauce.Therefore,the intensity of soy sauce aroma is related to the fermentation time and complex microorganisms.For brewing soy sauce,4-ethyl guaiacol(4-EG)is a key aroma substance,which has become a consensus in the sauce manufacturing industry.At present,there are few reports about how to produce 4-EG by the biotransformation pathway.In-depth research on the processes and microorganisms that can produce 4-EG,which can increase the content of 4-EG in traditional soy sauce products.This is significant for improving the quality of soy sauce.In present study,a strain G08 that could transform ferulic acid(FA)to produce 4-EG was screened out based on the microorganism and the ferment process,the fermented sauce mash was the raw material,and the content of 4-EG in the fermentation products as the inspection index by GC-MS detection and analysis.HPLC method was established to detect the changes in the content of various substances in the fermentation process of strain G08.Finally,the molar conversion rate of strain G08 transform FA to produce 4-EG could reach 7.92%.The transformation properties of each components of strain G08 were studied.It was found that extracellular enzymes secreted by strain G08 played a major role in the transformation process of FA to 4-EG.The strain was identified as B.subtilis G08 by morphological characteristics observation,physiological and biochemical tests,and molecular biological identification.The biological characteristics of strain G08 were studied.It was found that 35±2? was suitable temperature range for the growth of strain G08,and the strain grew to the stable stage after 18 h culture,and the tolerance to Na Cl could reach 9%.The effects of fermentation temperature,initial FA concentration and Na Cl content on the4-EG molar conversion in the fermentation experiment of strain G08 were studied.According to the response surface design,the optimal fermentation parameters of strain G08 were obtained: The fermentation temperature was 35.37?,the initial concentration of FA was922.42 mg/L,and the content of Na Cl was 0.92 %.The experimental conditions which were close to the predicted conditions of the model were selected to test verifiably,and the molar conversion rate was 8.32%.The enzymatic activity of ferulic esterase in Aspergillus niger and Aspergillus oryzae was2.506 U/m L and 1.188 U/m L respectively.Several methods of extracting FA from wheat bran by enzymatic hydrolysis with crude enzyme fluid were studied.It was found that the basic reflux extraction method was better than the enzymatic hydrolysis with biological enzyme solution,but it consumed much energy and was easy to cause pollution,while the enzymatic hydrolysis with Aspergillus niger was more effective than the enzymatic hydrolysis with Aspergillus oryzae or mixed enzyme fluid.The effects of enzymatic hydrolysis temperature,enzymatic hydrolysis time,liquid-solid ratio and p H value on the FA yield from wheat bran enzymatic hydrolysis by Aspergillus niger were studied,and the enzymatic hydrolysis conditions were optimized by orthogonal experimental design: enzymatic hydrolysis temperature was 40?,enzymatic hydrolysis time was 120 min,liquid-solid ratio(v/w)was 25:1 m L/g,enzymatic hydrolysis of p H value was8,the FA yield was 0.331%.The wheat bran was enzymolyzed by Aspergillus niger to obtain the enzymolysis fluid containing FA.The enzymolysis fluid was concentrated and used as the fermentation medium.After the fermentation of strain G08,4-EG was produced.GC-MS was used to detect flavor substances in the fermented product,and the content of 4-EG was 49.42 mg/L. |
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