Study On Fermentation Characteristics Of Mixed Bacteria In Compound Juice And Quality Change During Storage

Taking lactic acid bacteria and Gluconacetobacter xylinus as initial starting strains.The fermentation characteristics of lactic acid bacteria,the effects of mixed fermentation and different pretreatment on latic acid bacteria and fruit juices substrates were studied with yacon,litchi and longan as raw materials,which provide theoretical guidance for the research and development of mixed fermentation products of fruit juice.The main results are as follows:(1)Four different LAB(Lactobacillus casei,Lactobacillus plantarum,Lactobacillus rhamnosus and Lactobacillus acidophilus)were added to yacon juice for fermentation.The changes of lactic acid bacteria viability,soluble solids,pH value,titrable acid,sugar composition,et al during fermentation were compared.The results showed that the number of live bacteria reached above 8.00 log CFU/mL after 36 hours of fermentation.Among them,Lactobacillus rhamnosus had a slightly stronger fermentation ability to reduce sugar and produce acid compared to strains,and the browning index of the fermented yacon juice was significantly was 0.75,and the comprehensive sensory score was 85.80,which was better than the other three groups of fermentation juice.(2)The effects of single fermentation of Lactobacillus casei,Lactobacillus plantarum and Lactobacillus rhamnosus and co-fermentation with Gluconacetobacter xylinus on the growth characteristics of Lactobacillus,gastrointestinal tract tolerance,main nutritional components and antioxidant capacity in YLL juice(Yacon,Litchi and Longan)were studied.The results showed that after 24 hours of fermentation,the number of live bacteria was above 8.50 log CFU/mL,the survival rate of lactic acid bacteria in each fermentation group digested by artificial gastric juice and intestinal juice was above 60.00%.The survival rate of bile salt and in vitro digestion of lactic acid bacteria was higher than that of MRS broth fermentation group.Co-fermentation with Gluconacetobacter xylinus could improved the survivl rate of bile salt and in vitro digestion of lactic acid bacteria.After fermentation,the pH value of compound juice decreased to less than 3.90,and the content of lactic acid and oxygen radical absorbance capacity(ORAC value)increased significantly(p < 0.05).The co-fermentation of Gluconacetobacter xylinus and Lactobacillus rhamnosus significantly reduced the content of monosaccharide in YLL juice and increased the yield of acetic acid and cellulose(p < 0.05).Gluconacetobacter xylinus can improve the gastrointestinal tolerance of Lactobacillus rhamnosus to a certain extent,reduce the monosaccharide content of YLL juice,increase the acidity of juice and the content of edible cellulose.(3)Lactobacillus rhamnosus and Gluconacetobacter xylinus were inoculated into two kinds of compound juice with different pretreatments(heat sterilization and high hydrostatic pressure sterilization)for mixed fermentation,and the nutritional quality,flavor and storage stability of the fermented juice were compared.The results showed that the nutrition and flavor of fresh juice were almost the same after high hydrostatic pressure treatment.After 48 hours of co-fermentation,the number of viable bacteria in heat treatment group and high hydrostatic pressure group reached 9.40 log CFU/mL.The yield of polysaccharide reached 56.71 mg/L and 67.02 mg/L,respectively.The content of bitter free amino acids decreased by 89% and 87%,and the total content of volatile flavor compounds increased by 51.40% and 56.47%,respectively.After 28 days of storage,the number of live Lactobacillus rhamnosus in YLL juice fermented by heat treatment group and high hydrostatic pressure group was higher than 9.00 log CFU/mL.There was no significant change in the total sugar content.The total amount of six organic acids increased by 7.96 g/L and 7.94 g/L before and after storage,and the total phenolic acid content remained 45.55% and 46.16% respectively.In conclusion,high hydrostatic pressure treatment can ensure the microbial safety,nutritional quality and sensory flavor of compound juice,and mixed fermentation can improve the quality of compound juice,especially amino acid composition and volatile flavor components.