Probiotic Properties Of Salt-tolerant Lactic Acid Bacteria And Their Applications In Food Fermentation

Salt-tolerant lactic acid bacteria（LAB）widely exist in fermented foods,and they are closely related to the process of food fermentation and the formation of flavor substances.Studying the probiotic,safety,and metabolic characteristics of salt-tolerant LAB is of great importance for revealing the adaptation of them to the environment and their functions related to food fermentation.This study aims on investigation of the probiotic,stress resistant properties,and safety of Weissella and Pediococcus isolated from soy sauce moromi.The exploration of their functions in participation of food fermentation and their impact on flavor and quality of fermented food,may lay a theoretical foundation for elucidating the function of LAB for food fermentation and developing functional fermented food.The main research results are as follows:（1）Probiotic characteristics and stress resistance capability of salt-tolerant LAB have been demonstrated.The results showed that 5 LAB strains from soy sauce moromi were able to grow under low salinity(50 g·L^-1 Na Cl),and were tolerant to medium to high salinity(100 g·L^-1 and150 g·L^-1 Na Cl).These salt-tolerant LAB show low hydrophobicity and good antioxidant capability（scavenging capacity of over 50%DPPH（1,1-diphenyl-2-picrylhydrazyl）free radicals）,and can inhibit pathogenic bacteria such as Escherichia coli and Salmonella typhimurium.Among them,Pediococcus acidilactici WT1 has the highest tolerance to gastric acid,bile salt,and lysozyme,as well as the highest survival rate（85%）after lyophilization treatment.（2）The potential of salt-tolerant LAB in reducing lipids was revealed.It was found that salt-tolerant LAB could reduce the accumulation of intracellular triglycerides and accelerate lipid metabolism in mouse 3T3-L1 preadipocytes through down-regulating the expression of adipogenic transcription factor genes（PPAR-γ,C/EBP-α,a P2,FAS）and up-regulating the expression of adipogenic oxidation gene（CPT-1α）when co-cultured with the cells.Among them,P.acidilactici WT1 and Weissella paramesenteroides JL-5 significantly reduced the content of intracellular triglycerides,demonstrated their potential capability in reducing lipogenesis.（3）The safety of P.acidilactici WT1 has been evaluated and confirmed to be edible.No genes related to pathogenesis and antibiotic resistance are found in the genome of P.acidilactici WT1,based on the whole genome sequencing,gene annotation and gene scanning.Other food safety-related characteristics of P.acidilactici WT1 were further investigated.It was found that P.acidilactici WT1 was not hemolytic,hardly synthesized D-lactic acid,and was not pathogenic to animals.（4）The function of P.acidilactici WT1 in food fermentation was preliminarily studied.The contents of amino acid nitrogen,organic acids and total volatiles in high-salt dilute soy sauce were increased by 11.03%,34.42%,and 111.83%,respectively,through P.acidilactici WT1 synergistic fermentation.And the application of P.acidilactici WT1 for oat milk fermentation was also successfully.The LAB population reached 1.87×10⁹ CFU·m L^-1,and the content of free amino acids and essential amino acids increased by 36.93%and 137.11%in fermented oat milk.The content of total phenols and flavonoids in fermented oat milk increased by 344.97%and 295.05%,respectively.