Study On The Preparation Conditions Of Lactic Acid Bacteria Mixed Fermented Soymilk

Soymilk is a nutritious and comprehensive food containing high quality protein,but its promotion is limited due to problems such as bean smell.Fermentation is an effective means to improve the flavor,storage stability and functional properties of food products.In this study,fermented mixed soymilk was used as the research object to determine the combination of lactic acid bacteria strains with good fermentation characteristics to ferment mixed soymilk,to investigate the effects of process parameters such as mixing ratio and soymilk protein content on sensory scores and stability of fermented mixed soymilk,and to determine the best preparation method for preparing mixed fermented soymilk,and to conduct an in-depth study on its storage and functional properties.The main studies were as follows:Study on the effect of different combinations of lactic acid bacteria strains on the quality of mixed fermented soymilk.Lactobacillus fermentans grx08,Lactobacillus plantarum grx16,Streptococcus thermophilus grx02 and Streptococcus thermophilus grx90 were used for the combined fermentation soymilk and milk blending systems to investigate the effects of different strain combinations on the physicochemical indexes,sensory scores and volatile flavors of mixed fermented soymilk.The results showed that the combination of grx02 and grx16 fermented mixed soymilk only required 8.30 h to reach 73.38°T with 8.37 log cfu/mL of cocci and 7.17 log cfu/mL of bacilli.the volatile compounds species and contents in fermented soymilk were analyzed by GCMS,and it was found that compared with other fermentation groups,grx02 and grx16 combination of fermented soymilk could increase the content of 2,3-butanedione and 2,3-pentanedione,and minimize the content of undesirable compounds such as hexanol and 2-pentylfuran,which gave good flavor to the mixed fermented soymilk.Study on the preparation conditions and methods of mixed fermented soymilk.Single-factor and response surface tests were used to optimize the experimental methods,and the process parameters:acidity,sucrose addition,milk to soymilk mixture ratio,protein content,and protein content were optimized for two preparation methods,i.e.,mixing milk with soymilk in proportion before fermentation(abbreviated as:MFSM);fermenting milk alone,acidifying at 4℃ for 24 h,and then mixing with soymilk in proportion(abbreviated as:SMFSM).The fermented soymilk samples prepared by the MFSM method had an acidity of 70 °T,a sucrose addition of 8%,a buttermilk to soymilk mixing ratio of 1.5:1,and a protein content of 3.5%,with sensory scores of 90.15 points,a viscosity of 6248.57 cP,and a water holding capacity of 73.54%.The fermentation time was 8.30 h,the number of cocci was 8.37 log cfu/mL,the number of bacilli was 7.17 log cfu/mL,the chewiness was 5.11 mJ,the hardness was 0.25 N,the cohesiveness was 0.61,and the gumminess was 0.15 mJ,which gave the product good quality.Storage and functional properties study of mixed fermented soymilk.The storage and functional properties of the products prepared by MFSM method were monitored.The results showed that the acidity of the mixed fermented soymilk only increased by 4.17 °T and the pH only decreased by 0.05 during storage,followed by a weak acidification ability,which allowed the product to maintain good quality during storage,maintain sufficient amounts of active probiotics during storage,maintain better textural characteristics and better sensory scores.Higher levels of 2,3-butanedione,2,3pentanedione and ethyl coupling were detected at d 0 and d 7,which could impart aromatic flavor,lactic and soy aroma to the mixed fermented soymilk samples and improve the sensory quality of the mixed fermented soymilk.the product prepared in MFSM way contained 8.96 mg/L of acetic acid,7.65 mg/L of lactic acid and 1.65 mg/L of citric acid,and the fermentation was able to significantly increase the content of glycosides such as soy flavin and genistein,which are easily digested and absorbed by the intestinal tract,and to significantly improve their antioxidant capacity.