Application Of Lactobacillus Delbrueckii Subsp.Bulgaricus M-58 In Fermented Soy Milk

Fermented soy milk has become one of the hot spots because of its rich nutrition and unique health care function.Lactobacillus bulgaricus M-58 has excellent fermentation characteristics in fermented soy milk,and can be used as a commercial starter culture potential fermentation strain for systematic research.In this study,the composition and fermentation temperature of Lactobacillus bulgaricus M-58 fermented soymilk were determined by univariate experiment,and the fermentation characteristics of soymilk and storage characteristics of fermented products were monitored by using Lactobacillus bulgaricus M-58 fermented soy milk as the experimental group and commercial plant-based starter culture as the control group.The metabolites of fermented soy milk were determined by solid-phase microextraction coupled with gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry,and the effects of Lactobacillus bulgaricus M-58 on the flavor and quality of soymilk after fermentation were analyzed,in order to provide ideas and data support for commercial application.The conclusions are as follows:(1)Through univariate test and comprehensive analysis of response surface,the conditions for fermentation of soymilk by Lactobacillus bulgaricus M-58 are:the amount of glucose and sucrose added is 1.0%and 7.0%,protein content 2.6%,inoculation amount4.0×10~6CFU/m L,and the fermentation temperature of 42°C,the actual fermentation time is10.9h.(2)The volatile flavor substances in the fermented soy milk samples of the experimental group and the control group were detected,and the content of hexanal and hexanol,which mainly caused the bean smell after fermentation,was significantly reduced compared with the original soy milk,which were reduced by 80%and 22%in the experimental group and87%and 36%in the control group,respectively;Other beany-flavored substances are less content,but there is still a small residue.At the same time,the content of acetophenone,isoamyl acetate and isopropyl benzoate and other substances with aromatic flavor increased,the experimental group increased by 100%,152%and 44%,and the control group increased by 72%,180%and 56%,which brought various fruits,floral aromas and milky flavors to fermented soy milk,effectively masking the beany flavor.(3)Through the analysis of the non-volatile metabolite changes in the experimental group and the control group,linoleic acid and linolenic acid,the main substrates of the oxidation of soy milk to produce the beany flavor,were reduced after fermentation,and the decrease was large in the experimental group.The metabolism of lactic acid bacteria led to an increase in the concentration of free amino acids and the content of active soy isoflavones after fermentation of soy milk,and the stachyose in the experimental group decreased significantly compared with the control group.The cluster heat map showed that there were significant changes in the metabolite content of the experimental group,the control group and the raw soy milk,while the difference between the experimental group and the control group was not obvious(4)The stability of the experimental group during fermentation was higher than that of the control group,and the microrheological results showed that the time required for the experimental group and the control group to reach the gel point was 5.5h and 3.5h,respectively,and the experimental group had a weak gel structure.During storage for 21days,the acidity of the experimental group and the control group increased,the number of viable bacteria decreased,and the number of viable bacteria was greater than 1×10~7CFU/m L,and the viscosity and water holding capacity of fermented soymilk of the two groups increased in the first 14 days and then showed a downward trend,with significant differences(P<0.05).The sensory evaluation results showed that the experimental group had similar and better scores on smell and taste than the control group,but the experimental group scored lower in terms of tissue state and color.In summary,Lactobacillus bulgaricus M-58 has the potential of a professional starter culture for soy milk in the future.