Effects Of Mixed Fermentation Of Lactic Acid Bacteria And Yeast On The Quality Of Tofu

Tofu whey can be fermented in natural environment with its own microorganisms to form acid slurry.Acid slurry can be used as coagulant,which has fine texture and good water retention,but has obvious sour taste.In addition,there is no scientific basis for fermentation end point,and it is mostly based on human experience.In actual production,it is also easily affected by environment,temperature and seasonal changes,leading to the different quality of tofu;moreover,due to the natural fermentation varieties,there are many kinds of microorganisms,which may lead to the reproduction of harmful bacteria and limits the development of tofu industry.In this study,tofu whey was used as raw material to produce a new type of tofu coagulant,which was fermented by Lactobacillus rhamnosus and Saccharomyces cerevisiae.The viable number,pH,acidity,color difference and flavor of tofu acid slurry in different fermentation proportion were analyzed.The texture,water retention cooking resistance,oxidation resistance,protein content and amino acid content of acid slurry tofu,MgCl2 tofu and Lactic acid tofu were compared.The differences of flavor and volatile substances among acid slurry tofu,MgCl2 tofu and Lactic acid tofu were analyzed by electronic nose and GC-MS,and the effects of acid slurry on the protein structure and microstructure of tofu were analyzed.The results are as follows:Lactobacillus rhamnosus and Saccharomyces cerevisiae fermented tofu whey AS1,AS2,AS3,AS4 and AS5 respectively according to different proportion of 4:1,3:2,1:1,2:3 And 1:4.The results of pH value showed that the pH value of all acid slurry decreased with the prolongation of fermentation time,and AS1 had the lowest pH value;the result of acidity is consistent with that of pH value.generally,all acid slurry can meet the pH and acidity standard required by the test.The results of color difference showed that AS 1 had the highest brightness,red and green values,and the lowest yellow and blue values,followed by AS3.The results of electronic nose showed that the acid slurry was different from the tofu whey in its unique flavor.The results showed that the number of Lactobacillus rhamnosus and Saccharomyces cerevisiae were increasing with the extension of fermentation time,except for AS2.Considering the subsequent factory scaleup and the convenience of operation,AS3 was prepared by fermenting Lactobacillus rhamnosus and Saccharomyces cerevisiae in the proportion of 1:1,which can meet the test requirements.The results showed that the texture of ASTF3 was close to that of MTF and RTF;b value of acid slurry tofu was not significantly different from that of MTF and RTF,the color of tofu was yellow and had good brightness;compared with MTF and RTF,acid slurry tofu had good water retention and cooking resistance,and the comprehensive comparison showed that ASTF3 performed best;the sensory evaluation score of ASTF3 was 89.89,higher than that of MTF and RTF.The protein content of ASTF3 was higher than that of MTF and RTF;The content of leucine,isoleucine,phenylalanine and other essential amino acids in acid slurry tofu was higher than that of MTF and RTF,and EAA/TAA value was closer to that of FAO/WHO,and the value ofA STF3 was the highest.Through correlation and principal component analysis,different tofu scores were calculated by the comprehensive evaluation model.ASTF3 score was 0.757,ranking first,higher than that of MTF(-0.939)and RTF(0.219).The results showed that the acid slurry tofu had good antioxidant capacity and there were differences among different acid slurry tofu.The results of electronic nose showed that the flavor of MTF and RTF was similar,and acid slurry tofu had unique flavor different from MTF and RTF;GC-MS showed that the content of alcohol and other bad flavor substances in tofu was MTF>ASTF3>RTF;the content of aldehyde,ester and ketone was ASTF3>RTF>MTF.The results of SDS-PAGE showed that there were differences in the optical density values of tofu protein bands,and the content of 11S globulin in acid slurry tofu was relatively high;the ?-folding content of RTF and MTF is high,and the protein structure is relatively compact.The ?-folding content of acid slurry tofu made from acid slurry is reduced,and ?-helix is increased;the total free sulfhydryl content of protein can be increased by acid slurry;the microstructure of RTF and MTF is relatively close,and the structure of acid slurry tofu is loose and porous,showing spongy,and the distribution of Lactobacillus rhamnosus and Saccharomyces cerevisiae in tofu was also observed apparently.