The Study Of Enshi Traditional Sufu Processing Technology Characteristics,Physicochemical And Antioxidant Properties

After being decomposed by microorganisms,sufu produces various amino acids,peptides and flavonoid aglycones,which is beneficial to human digestion and absorption,and produces special tasty taste and aroma that can increase people’s appetite at the same time.In recent years,the nutrition,functional factors and flavor of pickled tofu in Beijing,Kedong County in Heilongjiang province,Shaoxing city in Zhejiang,Chengdu and Yibin cities in Sichuan,Guilin city in Guangxi,Guangzhou in Guangdong has been studied successively,which showing that more researchers have much interest in the local characteristic products.However,there is no systematic study of sufu in Enshi,the ethnic area with its unique terrain,climate and food habits.Therefore,we selected five famous kinds of local traditional sufu,and investigate its production process,and analyze its texture,basic nutrition,flavor and antioxidant activity,which in order to show the quality traits of traditional sufu and lay the foundation for the future quality standard formulation and the standardization of production of sufu in Enshi.The research results are as the following:The basic processing techniques for making sufu are generally the same,but the details have their own characteristics.The basic production process of Sufu is as follows:bean curd-Natural Fermentation-liquor extinguishing-coated condiments-canning and so on.But the results of the investigation showed that the processing details of making the 5 kinds of characteristic sufu were different.The material of sufu can be a common bean curd and squeezed water old tofu;fermented naturally in wooden or straw;many kinds of spices are also different,some sufu leaves coated and wrapped parcels,then filled in the container,some soaked into edible oil soaked,some just kept dry and don’t added any liquid,and then for post-fermentation.After careful observation of the surface bacteria of sufu blank,it is found that the color of fermented bacteria was different from that of mycelium.It has both single mold and mixed mold,and the interaction between mold and bacteria,so the appearance,texture and flavor of the product are also different.Chemical composition and texture characteristics of sufu.The moisture content of the 5 kinds sufu is about 60%,the total protein content is 11.26-15.66g/100g,soluble protein is 3.94-7.24g/100g,amino nitrogen is 0.56-1.95g/100g,the total amino acid content is of 0.668-3.473g/100g,the essential amino acids of 0.403-20.74g/100g,total acid content is 0.32-0.78g/100g,the salt content is 7.90-10.82 g/100g,the fat content is 5.88-14.46 g/100g,and the volatile basic nitrogen for 0.12-0.34 g/100g.The Hardness of the sufu is 82.64-439.04g,the Adhesiveness is 9.39-167.70g/s,and the Springiness is 0.27-0.86.The chemical composition of sufu had an important effect on texture.The results showed that the hardness,adhesiveness,springiness,gumminess and chewiness of sufu had a significant positive correlation with total protein,and negatively correlated with WP/CP（water soluble protein/total protein）and total acid.In addition,adhesiveness,springiness,cohesiveness,viscosity and chewiness were negatively correlated with salt content.Hardness,gumminess and chewiness were significantly correlated with moisture content.The volatile flavor components were different greatly between the sufu blank and the sufu finished products.47 kinds of volatile components were measured in 5 kinds of sufu blank,and 98 kinds of volatile components were measured in 5 kinds of sufu products.The volatile compounds of sufu blank were mainly composed produced by fermentation,and were composed of raw material of esters and protein decomposition products such as indole,phenol and a small amount of amine.The volatile components of sufu finished products were mainly produced by the esterification reaction during fermentation period.Comparing with the reported volatile components in finished products,it has some unique sabinene,myrcene,α-phellandrene,α-terpineol,linalool enol substance,and a large number of substances（e.g.linalyl formate linalyl acetate,etc.）indicating that Enshi pickled tofu has its unique flavor.Sufu has certain antioxidant activity,and sufu blanks’antioxidant activity is higher than that of finished products.It is found that the sufu samples have a good linear relationship with the clearance of DPPH,·OH and O₂^-·in the range of 5.0-45.0mg,5.0-25.0 mg and 5.0-25.0 mg respectively.The IC₅₀ on DPPH,·OH and O₂^-·of sufu blank are between 16.91-38.45mg、10.33-22.77 mg and 13.84-23.42 mg,The IC₅₀ of sufu products are between 37.69-43.06 mg,20.16-26.50 mg and21.87-27.46mg.The results showed that the scavenging capacity of sufu samples to DPPH,·OH and O₂^-·were different.Partial correlation analysis between the antioxidant activity and the components of sufu shows that:water soluble proteins and isoflavones are the main antioxidant active substances in the water extract,and their partial correlation coefficients with the clearance rates of DPPH,·OH and O₂^-·are0.471,0.671,0.600 and 0.585,0.318 and 0.443 respectively.The regression equation of the chemical constituents and free radical scavenging ability is:the DPPH clearance rate（%）=18.746X₁+22.549X₂-74.499X₃+154.087X₄+0.914X₅+5.394.·OH radical scavenging rate（%）=79.297X₁-59.022X₂-57.566X₃+178.358X₄-104.516X₅-4.334,O₂^-·radical scavenging rate（%）=41.909X1+15.1X2-95.122X3+167.496X4-71.099X5+14.472.Finally,through comprehensively evaluation of the nutritional components,texture,flavor and antioxidation of sufu,it showed that the qualities of No.3 and No.4sufu were better.It is recommended to select fine strains from 3 or 4 sufu for the Enshi sufu in the future;the hardness of the product should be suitable for 200-400g,and appropriate ethanol or salt can be added to the fermentation process to adjust the hardness in order to achieve the best texture;the packaging can be made of vegetable leaves or oil.