| The emergence of this phenomenon has happened in the actual processing of the Mucor type douchi in the processing of the fermentation:benzoic acid, propionic acid has not been added in production,which was detected in douchi product.The manufacturers are very confused. To answer this question, in order to meet consumers’requirements of douchi about nutritional, sensory, health, quality and safety, we must find the answer to this question which requires studying the relevant components of the changes in douchi fermentation process with a full understanding of in-depth discussion of the relationship between the microbial fermentation process and its related enzyme activity and composition changes, in order to complete the study on the mechanism of benzoic acid、propionic acid formation in the Mucor type douchi. In this study, we sampled the Yongchuan traditional fermentation of Mucor douchi at different times and the post-fermentation process, study the entire process involved in benzoic acid, the material content propionic acid formation and activity indicators for dynamic tracking.The purpose is to sort out relationship between the various substances、microbes、secreted enzymes with benzoic acid and the propionic acid and to understand the mechanism of its composition changes. This paper came to the following conclusions:1) From the research of the benzoic acid formed mechanism during Yongchuan Mucor type douchi in the processing stage.The result shows that:in the first two days of the koji (S3), benzoic acid content is 2.43mg/kg, then its content has been increasing to achieve 37.23mg/kg of the koji 215 days after fermentation (S14); and phenylpropanoid acid content increased from the raw soybeans 4.89mg/100g S14 to achieve 272.23mg/100g;The content of the intermediatesβ-cinnamic acid is higher in the koji stage,then reduced gradually in the post-fermentation stage, and found that benzoic acid has increased quickly in the content of the koji stage when the content of B-cinnamic acid is high,the trend of increasing is not obvious in the after-fermentation stage; At the same time, phenylalanine ammonia-lyase enzyme (PAL) activity catalytic phenylalanine that converted to B-cinnamic acid stay strong in the koji stage strong, weakened gradually in the post-fermentation stage. Under the research, Mucor type douchi benzoic acid formation mechanism may be as follows:soybean protein first partially hydrolyzed into amino acids, the phenylalanine convert to B-cinnamic acid by the phenylalanine ammonia lyase’(PAL) catalytic, B-cinnamic acid finally oxidated to the benzoic acid under certain conditions.(2) From the reseach of the Yongchuan Mucor type douchi Formation Mechanism of propionic acid in the processing.The results show that:propionic acid has been detected in the raw soybean koji acid, but the content is lower about 37 mg/kg, according to the police, which is added for storage, but the propionic acid content was increasing significantly in the first four days of the koji (S4). the propionic acid content of 215 days after-fermentation (S14) rised to the maximum 189mg/kg with koji time extented. Intermediate product pyruvate is higher in the content of the koji stage in the first two days of the koji,the content is about 22mg/kg,the koji content reached a maximum 160mg/kg (S8) in the first 10 days.The content has maintained at around 70mg/kg in the fermentation process;The result shows that there is a material conversing to pyruvate, but consuming in the same time. Propionic acid increased evidently in the koji phase when the content of Pyruvate is high,increased slow in the after-fermentation stage; catalytic carbon source for propionic acid bacteria polysaccharides into monosaccharides and oligosaccharides cellulase and glucoamylase activity in the koji stage in the post-fermentation stage gradually weakened. Fumaric acid intermediates from pyruvate to propionate in the propionic acid fermentation process, detected in the first two days of the koji (S3), fumaric acid, content of 2.3mg/kg at this stage propionic acid content increased significantly. At the end of the time of koji, fumaric acid content decreased in the fermentation stage, the trend of propionate increasing slowed down. When the fumaric acid content is small, the propionic acid content maintain about 189.22mg/kg. Suspected of propionic acid bacteria strains BS has been isolated in douchi samples of koji stage, with the observation of colonial morphology, microscopic observation, physiological and biochemical identification and glucose acid production process determination,it can be concluded an initial period of the propionic acid bacteria.So the possibility of conclusions are as follows. First pathway of Propionic acid formation:cellulase and glucoamylase hydrolysis of soybean tempeh produced by microbial fermentation in the process of carbohydrates such as cellulose, polysaccharides, oligosaccharides, and generate propionic acidreducing sugar that produced by the bacteria can be directly used by propionic acid bacteria and then reducing sugar fermentation pyruvate, another part of the reducing sugar can also generate pyruvate part of the mold and bacteria, Pyruvate became fumaric acid first under the action of propionic acid bacteria, then fumaric became propionic. Sencond pathway of Propionic acid formation:tempeh in the free amino acids such as L-alanine, L-Serine, L-cysteine transfer amino deamination to pyruvate generated pyruvic acid first,then generates propionic acid by the propionic acid bacteria metabolism(3) From the research of the changes happened in carbohydrate the Yongchuan Mucor douchi in the process. The results show that:the cellulase activity of the sample rise slow in the koji process, and achieve to maximum 1.3672U/g in the post-fermentation, followed by rapid decline, and finally almost be zero, whose activity directly affects the size of cellulose hydrolysis into the speed of the monosaccharide. Glucoamylase activity increased gradually to reach maximum 107.27U/g in the late koji stage, then decreased gradually in the post-fermentation process, and finally maintained at about 45U/g in the koji process. Remove moisture, total sugar fell down from 27.69% of the raw materials to the 1.87 percent in the finished product; Reducing sugar content increased gradually in the process of koji, achieve 7.69% in the post-fermentation, and then gradually decreased to 1.36% in the finished product. Reducing sugars that as the product of microbial fermentation in the middle, on the one hand increased because the decomposition of the total sugar, on the other hand is consumed as microbial carbon source, which provide a material guarantee for the formation of pyruvate. |
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