Study On Flavor And Antioxidant Activity Of Potential Probiotics Fermented Ginger Flavored Black Soy Yogurt

Black soybean and ginger were selected as materials,the strain was isolated from naturally plant-derived fermented food,microfluidization was used to obtain a new type of soy yogurt product.The probiotic properties of the selected lactic acid bacteria were studied.Then the physicochemical properties,rheological properties,microstructure,sensory and antioxidant activity of the ginger flavored black soybean yogurts were studied.Firstly,two strains of bacteria were isolated from natural fermented pea beans.The strains were identified by morphological observation and 16 S rDNA gene sequence analysis.The results showed that strain NO1 was Lactobacillus casei and strain NO2 was Lactobacillus plantrum.Relative to the commercial control strain L.casei-01,the acid resistance,bile resistance,gastrointestinal tolerance,bacteriostatic capacity and drug resistance of Lactobacillus casei NO1,Lactobacillus plantrum NO2 and Streptococcus thermophilus ST3 were determined.The strain Lactobacillus casei NO1 and Lactobacillus plantrum NO2 have strong tolerance to the artificial intestinal juice and 0.3% bile salts.The strains Lactobacillus casei NO1,Lactobacillus plantrum NO2 and Streptococcus thermophilus ST3 all have strong adhesion to Caco-2 cells,no drug resistance.Besides,they also have strong inhibition ability against enteropathogenic bacteria such as E.coli O157,Staphylococcus aureus,Listeria monocytogenes.Secondly,the characteristics of ginger flavored black soy yogurts were studied.Choosing L.casei-01 as a control,combined Lactobacillus casei NO1,Lactobacillus plantarum NO2,and Lactobacillus helveticus LH-B02 with Streptococcus thermophilus ST3 were used as fermentation culture to prepare ginger flavored black soy yogurts.We studied the samples SYC-1 and SYP which were prepared by Lactobacillus casei NO1,Lactobacillus plantarum NO2 combined with Streptococcus thermophilus ST3: the results showed that although the acidity values of samples SYC-1 and SYP were slightly lower,they all had stronger water holding capacity,better rheological characteristics,higher sensory evaluation and stronger antioxidative activity.Among them,the sample SYP had the strongest water holding capacity of 72.01%,the highest overall acceptability score of 8.04,the highest DPPH scavenging capacity of 72.38μmol Trolox/mL,the highest ABTS scavenging capacity of 1.63 mmol Trolox/mL,and FRAP of 399.29 mmol Trolox/mL.In addition,samples SYC-1 and SYP have large yield stress τ0 and hysteresis loop HL,and the microstructure is tight,but there are still large pores in the three-dimensional gel network structure.Finally,the effects of microfluidization of soymilk on the characteristics of soy yogurts were discussed.As revealed by results,microfluidization significantly enhanced acidity,water holding capacity and sensory quality of ginger flavored black soy yoghurt.Samples elaborated from microfluidized displayed higher viscoelasticity and consistency.Micrographs of SEM demonstrated that,after microfluidization,gel of ginger flavored black soy yogurts became denser,and holes of protein networks became lesser and smaller.Microfluidization significantly increased the antioxidant activity of the yogurts,and the SYP scavenging DPPH capacity of the sample increased to 98.29μmol Trolox/mL;Further studies showed that microfluidization can promote the conversion of soybean isoflavone in the sample;GC-MS analysis also showed that the content of D-limonene with antioxidant activity was significantly higher in microfluidization-treated samples.Through the separation of potential probiotics and the determination of its probiotic function,combined with microfluidization,it was applied to the preparation of ginger flavored black soy yogurts,finally a ginger flavored black soy yogurt with high antioxidant activity and good flavor was obtained.It lays the foundation for enriching the industrial application of soybean yogurt.