Probiotic Complex Based On Metabolomics And In Vitro Bionic Digestive System Fermented Milk Characterization

Complex probiotic fermented milk as a good carrier can deliver probiotics to the human intestinal tract,and then play a probiotic effect.In this study,composite probiotic fermented milk was prepared with Bifidobacterium animalis subsp.lactis Probio-M8,Lacticaseibacillus rhamnosus Probio-M9 and Lactococcus lactis subsp.lactis BL19,and Lactococcus lactis subsp.lactis BL19 monobacterial fermentation was used as the control group to investigate the fermentation characteristics of composite probiotic fermented milk and monobacterial fermented milk,and to identify volatile flavor substances during storage and evaluate the survival of probiotics in the simulated gastrointestinal tract using solid-phase microextraction-gas chromatography-mass spectrometry(SPME-GC-MS)and dynamic in vitro bionic digestion techniques,with the following results.1.Compared with monobacterium fermented milk,compound fermented milk has faster fermentation curd,shorter fermentation time,and finally finished fermentation in about 8.5h(p H 4.5).During storage,compound fermented milk has moderate acidity,delicate taste,higher live bacteria count than standard and stable,and meets the requirements of yogurt index.2.A total of 89 volatile flavor substances such as aldehydes,ketones,acids,esters,alcohols,aromatics and alkanes were identified in the two groups of fermented milk during storage.Among them,the volatile flavor substances detected in the compounded fermented milk were significantly better than those in the monobacterial fermented milk in terms of type and content.The sensory evaluation score was also higher than that of monobacterium fermented milk.Characterization of key flavor substances detected in compounded fermented milk at the beginning of storage were 2-heptanone,4-octanone,5-hydroxy-2,7-dimethyl,and 2-nonanone.The key flavor substances characterized in late storage were 1-butanol,2-methyl,acetic acid,vinyl acetate,and 3-methylbutyraldehyde.3.The survival rate of fermented milk viable bacteria was significantly higher in 1d storage than in 21 d storage after dynamic bionic human gastrointestinal digestion of compound fermented milk and monobacterium fermented milk during storage.Further by electron scanning electron microscopy,it was found that the casein structure of fermented milk storage 21 d was loose and poorly wrapped around the strain,and part of the strain was exposed to the external environment;The fermented milk showed a significant decrease in β-galactosidase activity after 21 d of storage,indicating a decrease in the viability of the strain and a weakened tolerance to gastrointestinal fluids.This study provides basic data for the industrial production of Bifidobacterium animalis subsp.lactis Probio-M8 and Lacticaseibacillus rhamnosus Probio-M9 complex probiotic fermented milk.