Study On Key Technologies Of Semi-dried Tofu Processing And Aggregation Behavior Of Soy Proteins

Zhongxiang tofu is one of the local traditional characteristic foods in Hubei Province.Because of its unique flavor and quality,it has been favored by consumers.However,for a long time,the Zhongxiang tofu were made in small workshop or by private,with no advanced processing engineering,low output,unstable quality and short shelf life.These issues have seriously limited development tofu industry.It is imperative to study industrialization and standardization of Zhongxiang tofu production and improve product quality characteristics.This study aims at improving the quality characteristics of Zhongxiang tofu products and try to develop high quality and long shelf life of tofu,such as screened of soybean varieties and coagulants,optimized and improved production process and sterilization technology,and established HACCP management system of Zhongxiang tofu.It has also studied on the mechanism of soybean protein coagulation in tofu production.The main contents of this study are as follow:（1）The influences of soybean variety on the properties of Zhongxiang tofu were investigated.The yield,texture characteristics,main chemical components,sensory evaluation and micro-structure of soybean seeds of six different Zhongxiang tofu（prepared from different regions and varieties of soybean）were determined.The results showed that the content of the soybean proein,the soluble protein,the fat,the storage protein and their respective subunits were quite different from 6 varieties.The yield of tofu was significant positively correlated with water-soluble protein and moisture content of tofu,and extremely significant positively correlated with protein content,significant negatively correlated with fat content of soybean seeds.Brine processing can not eliminate the difference of tofu quality caused by different soybean varieties.The yield of Zhongxiang tofu prepared by Yu 25 was the highest,followed by Zhong 8,Wan 15 and Heinong 48 was the lowest,and the highest acceptance of sensory evaluation was Yu 25,followed by Zhong 8,Heinong 48.The comprehensive factor score showed that Yu 25,Zhong 8,Zhong 30 and Suinong 14 were the suitable varieties for Zhongxiang tofu processing.（2）the effect of coagulant type and concentration on the quality of Zhongxiang tofu was studied.The yield,texture and sensory evaluation of Zhongxiang tofu prepared by five coagulants（gypsum,calcium chloride,magnesium chloride,GDL and citric acid）were analyzed.The results showed that the change of coagulant concentration had a significant effect on the hardness and springiness of tofu.Except gypsum,the other four coagulant concentrations had a significant effect on tofu hardness and springiness.Chewiness had little effect.The yield and sensory evaluation of tofu prepared with 4.4%gypsum were the highest,followed by 1.6%GDL tofu,which was suitable for processing Zhongxiang tofu as coagulant.Taking all the aspects into sonsideration,including texture and taste,we chose Yu25 and gypsum as the source of tofu and coagulant,respectively,in the follow-up studies.（3）Taking yield rate and sensory evaluation as indices,this paper optimized the process parameters of Zhongxiang tofu production through quadratic regression orthogonal rotary combination design,and also studied the effect of water soybean rate,coagulant content,coagulant temperature,coagulant time,first press time on Zhongxiang tofu production.Analyzed the effect of factors on sensory quality and yield rate of tofu.Through the analysis of effect of integrative index by linear weighting method,the optimum process parameters of Zhongxiang tofu production are:water soybean rate 8,coagulant content 4.4%,coagulant temperature 75℃,coagulant time 20 min,first press time 15 min.（4）The effects of microwave sterilization and irradiation sterilization on the main nutritional components,texture characteristics,protein structure and microbial quantity of tofu were compared and analyzed.It was found that both ⁶⁰Co 6.0 KGy irradiation and microwave（800 W 60 s-60 s-60 s）sterilization methods had obvious sterilization effect on vacuum sealed packaging tofu,and the sterilization effect of irradiation was stronger than that of microwave sterilization.Irradiation treatment had a great effect on protein structure,but had little effect on the main chemical components,amino acid content,texture and color.Microwave treatment can increase the fat content of tofu.Compared with irradiation sterilization,it has greater effect on texture and color of tofu,but less effect on protein structure and amino acid content.（5）The aggregation behavior,configure and gel-forming mechanism of soybean protein in the process of tofu production.The chemical interactions and protein structures in order to maintain soybean protein structure and stability changed during tofu gel forming,which were correlated closely to forming procedure and tofu gel properties.Ion bonds decreased significantly,while disulfide bonds,hydrogen bonds and hydrophobicity increased significantly with tofu gel forming.The main chemical interactions to maintain tofu gel network structure were disulfide bonds,hydrogen bonds and hydrophobicity.The results of Ramman spectra indicating random coil,disulfide bonds and hydrophobicity were consistent with the change of chemical interactions.Circular Dichroism results of tofu forming also showed that the content of secondary structure of soybean protein were in a constant state of change,which were advantageous to stability and formation of new protein aggregates.（6）HACCP principles were applied to the hazard analysis of Zhongxiang tofu production,and the critical control points and corresponding critical limits were determined.Then the HACCP management system of Zhongxiang tofu was preliminary established.