Study On Mixed Fermentation Of Sufu With Mucor Racemosus And Rhizopus Oryzae

As traditional Chinese fermented soy foods and spices,sufu is made from soybean through a variety of microbial synergy fermentation.Sufu has a unique flavor,delicious taste and silky texture,which contains rich nutrients and flavor substances at the same time.The Production process of sufu was based on soybean as raw material,generated by pulping,blocking,primary fermentation,curing and secondary fermentation.The primary fermentation is very important to sufu for the overall transformation of nutrients,and the Mucor racemosus and Rhizopus oryzae are important strains in the process of primary fermentation.Firstly,this article optimized the technology of independent primary fermentation of Mucor racemosus and Rhizopus oryzae,analyzing free amino acids and volatile flavor components by combining the secondary fermentation process.In order to explore the effect of mixed fermentation,we researched the Mucor racemosus and Rhizopus oryzae fermentation sufu technology on the basis of separate fermentation,and explore main physicochemical property and structure changes of sufu in the process of three ways of fermentation.The similarities and differences in three ways of fermenting sufu were also studied.The study provides certain reference in exploring fermentation mechanism of pure bacteria of sufu collaborative primary exploration.The main results are as follows:(1)The research of primary fermentation with Mucor racemosus and Rhizopus oryzae in single colony.The primary fermentation conditions of Mucor racemosus and Rhizopus oryzae fermenting sufu were optimized respectly,in the method of response surface experiment design.The results are as follows: Mucor racemosus,the optimum conditions of fermentation time of 60 h,fermentation temperature of 24 ?,inoculums concentration of 1.0x10~5 CFU/Ml,the mean value of protease activity was 42.85 U/mL on this conditions;Rhizopus oryzae,the optimum conditions of fermentation time of 50 h,fermentation temperature of 32 ?,inoculums concentration of 1.0x10~5 CFU/m L,the mean value of protease activity was 33.51 U/mL on this conditions.The free amino acids and volatile flavor of sufu from Mucor racemosus and Rhizopus oryzae was analyzed by Automatic amino acid analyzer and GC-MS machine,respectively.Results showe the sufu contains 17 kinds of free amino acid(not including tryptophan)from the two ways of fermentation,including 7 essential amino acids and 5 flavor amino acids.Total free amino acid content in the sufu of Mucor racemosus is 4.56 g/100 g,essential amino acid content is 1.46 g/100 g,accounting for 32.02% of the total free amino acid content.Total free amino acid content in the sufu of Rhizopus oryzae is 4.08 g/100 g,essential amino acid content is 1.425 g/100 g,accounted for 34.93% of the total free amino acid content.61 kinds of volatile flavor substances were detected in Mucor racemosus sufu,accounted for 83.55% of the total volatile flavour compounds;53 kinds of volatile flavor substances were detected in Rhizopus oryzae sufu,accounted for 76.3% of total volatile flavor substances.There exists considerable difference in the type and content of Volatile flavor for the two kinds of sufu from Mucor racemosus and Rhizopus oryzae,especially alcohols,ester,aldehyde and acid compounds.(2)The mixed primary fermentation research of Mucor racemosus and Rhizopus oryzae.The mixed primary fermentation conditions of Mucor racemosus and Rhizopus oryzae fermenting sufu were optimized,in the method of response surface experiment design.The optimal primary fermentation conditions are as follows: fermentation time of 56 h,fermentation temperature of 28 ?,mix proportion of Mucor racemosus and Rhizopus oryzae is 1:1.Under those conditions,the mean value of protease activity and saccharifying enzyme activity was 50.51 U/mL and 15.15 U/m L respectively.Sensory characteristics and main enzyme activity of sufu billet from three methods of fermentation were comparied.The results show mixed fermentation can not only make up for some deficiencies of the fermentation,but play the advantages of single strain,which is a more comprehensive way than the two separate fermentation.This study makes a good foundation for a series of biochemical reactions in the process of after fermentation.(3)The changes of physiochemical properties and structure features of sufu embryo in mixed fermentation,Mucor racemosus fermentation and Rhizopus oryzae fermentation were studied respectively.With the process of fermentation,trends of changes in physiochemical properties(soluble protein,free amino acid nitrogen,free fatty acid and reducing sugar,total acid)are basically identical in three ways of fermentation.The final content of soluble protein and free amino acid nitrogen in mixed fermentation was higher than the Mucor racemosus and Rhizopus oryzae.There was a certain improvement on content of free fatty acid,reducing sugar and total acid in mixed fermentation,compared to Mucor racemosus fermentation.Along with the process of fermentation,trends of the quality and structure features(hardness,elasticity and adhesion)of sufu are basically identical.Changing rate of mixed fermentation of sufu was fastest,and finally the hardness and flexibility in mixed fermentation sufu are both lower than single bacterium fermentation,but adhesive is higher than single bacteria fermentation.So,mixed fermentation has a certain advantage.(4)In-depth analysis of free amino acid composition and volatile flavor components by mixed fermentation of sufu.Comparation of three ways of sufu fermentation in free amino acids and volatile flavor component,the total free amino acid content is up to 4.56 g/100 g in mixed sufu fermentation;the second was the Mucor racemosus sufu,4.56 g/100g;Rhizopus oryzae sufu is 4.08 g/100 g.By analyzing the free amino acid composition in sufu of mixed fermentation,the content of flavor amino acids was higher than single bacteria,as well as hydrophobic amino acids and essential amino acids.We detected 73 kinds of volatile component in mixed sufu fermentation and the relative content was up to 89.22%;61 species were detected in the fermented bean curd,and the relative content was 83.55%.51 species were detected in the root rot and the relative content was 76.3%.Mixed fermented bean curd flavor is better than single bacteria fermentation mixed fermented bean curd has certain advantages.Mixed fermentation sufu in physical and chemical properties,quality and structure features,free amino acids and volatile flavor material can not only keep the advantage of the single bacterium fermentation,still can make up for the inadequacy of single bacterium fermentation respectively,has a certain advantage.