Research On The Technique Of Processing Of Whole-soybean Sufu

Sufu is becoming increasingly popular worldwide because of its nutrition, distinctive taste and fine texture. The annual production of sufu is estimated to be over300,000metric tons in China. The traditional technique is used to remove okara and produce sufu. The utilization rate of soybean was found to be reduced and the majority of okara is discarded as industrial waste, which causes serious environmental problems if disposed improperly. In order to promote the utilization rate of soybean and to reduce the environmental problems caused by okara from the traditional processing method of sufu. The possibility of the whole-soybean sufu(WSS) processing method, which does not produce okara, was investigated. WSS is a new type of sufu. Compared with the traditional technique, no okara is produced during WSS processing. Therefore, the development of WSS production is both economically and environmentally advantageous.The study used peeled soybean as raw material and traditional sufu(TS) as comparison, we made a research on the production process and the key technology. The main research is:effects of process condition on characteristics of white billet of whole-seed sufu; the selecting of fermentation stain; the optimization of the fermentation condition with response surface methodology (RSM) applied; the changes in characteristics of WSS during fermentation; the analysis of WSS product. The main concludes are as follows:1. Effects of process condition on characteristics of white billet of whole-seed sufuThe peeled soybean was ultrafine pulverized by colloid mill, and the effects of coagulated temperature, the amount of coagulant, soymilk concentration on characteristics of white billet of whole-seed sufu were studied through single factor experiment and the orthogonal experiment. In the condition of colloid mill ground three times, the quality of white billet of whole-seed sufu was almost the same as the traditional ones. The proportion of bittern and gypsum was5:5. The optimal technogical parameters of coagulation were fixed:coagulated temperature80℃, the amount of coagulant3.0%, soymilk concentration12%.2. The selecting of fermentation strain and the optimization of fermentation conditions (1) The trials selected M.wutungkiao, Mucorsufu, M. Racemosus, Actinomucor elegans, four kinds of strain to test. They were cultivated on the same condition and secrete enzyme, using the proteinase, lipase, cellulase, amylase as the indicator, the amount of enzyme secreted by stains were determined. Finally, comprehensive consideration the state of enzyme secreting, selecting Actinomucor elegans as the fermentation strain.(2) The effects of fermentation time, fermentation temperature, inoculating amount on prophase fermentation of WSS through single factor experiment and the response surface methodology (RSM). The conclusion showes that the optimal fermentation conditions were:fermentation time54h,fermentation temperature30℃,inoculating amount10.3%.Under this optimal conditions,the activiy of proteinase was208.292U/g,lipase was95.835U/g,cellulase was62.479U/g, amylase was202.215U/g。(3)The effects of NaCl amount, fermentation temperature, alcohol content on anaphrase fermentation of WSS through single factor experiment and RSM. The conclusion shows that he optimal fermentation conditions were:NaCl amount12%, fermentation temperature29℃, alcohol content11.70%. Under this optimal conditions, the WSS was scored9.0points by sensory evaluation, fermentation time was7.0weeks.3. The changes in characteristics of WSS during fermentation(1)The changes in the content of protein, lipid, dietary fiber, crude polysaccharide were all decreased during ripening period. On the contrary, the changes in content of free fatty acid, reducing sugar, total acid, amino nitrogen were all increased during the entire fermentation period.Meanwhile, the content of isoflavone aglycone also increased, this phenomenon may attribute to B-glucosidase hydrolysis. The increase in the hardness of pehtze during prophase fermentation may be attributed to the white billet wrapped by the mycelia of A. elegans. The osmotic separation of salt and water may contributed to the increase in the hardness of salted pehtze. A continuous reduction in the hardness of sufu during anaphase fermentation may be attributed to the degradation of salted pehtze components caused by hydrolytic enzymes. During the entire fermentation period, the adhesiveness of WSS increased and the springness decreased.(2)The changes in microstructure of WSS was observed by scanning electron microscopy. The white billet of WSS microstructure showed a "honeycomb-like" structure with larger pores but a discontinuous, loose network. This structure is possibly responsible for the existence of cellulose and soybean polysaccharide, which hindered the formation of a fine network. Through prophase fermentation, the networks in WSS was not significantly damaged by the limited hydrolysis of enzymes, but a certain effect was observed. The network of ripened WSS was significantly destroyed, but small pores were still observed on the matrix to wrap the non-degraded cellulose and soybean polysaccharide.These pores are beneficial to the formation of the delicate tissue morphology of WSS.(3)Through GC-MS analysis of WSS, the result showed that kinds of volatile flavor compounds in increasing, especially the range of ester components and the special flavor of WSS was more and more intensed during entire fermentation.The identical degree of main flavor substances were above80%between WSS and TS.4. The analysis of WSS productTo determine and compare the sensory, physical and chemical, microbiological indicators of WSS and TS. The results showed that the quality of WSS was acceptable by comparison with traditional sufu and the shelf-life of12months was preliminary affirmed. Compared with TS, the yield of WSS increased by66.20%, the utilization of raw material increased by28.37%, with significant economic benifits.