Study On Fermentation Characteristics And Prebiotic Function Of Lactobacillus Delbrueckii From Tibet

Research background:The yak milk in the pasturing areas of the Tibetan Plateau is rich in resources,among which the ratio of lactic acid bacteria is significant.Lactic acid bacteria has the advantages of good organization,strong resistance to adverse effects,excellent probiotics and special flavor.The yogurts made by local herdsmen by traditional fermentation methods have delicate organization,pure taste,unique flavor and can maintain the status for a long time.These results indicate that yak yogurt contains excellent lactic acid bacteria with excellent curd condition,strong transmutation performance and unique taste,which is related to the specificity of probiotics created by the extreme environment in Tibet.Objective:To screen lactic acid bacteria strains with excellent fermentation characteristics and characteristic flavor substances,and to study and develop functional lactic acid bacteria with cholesterol-lowering,antioxidant and anoxic resistance.Method:The fermentation characteristics of lactic acid bacteria were determined by acidity titration national standard method,kit,phthalaldehyde colorimetric method,etc.Using Headspace solid-phase microextraction-gas chromatography-mass spectrometry,HS-SPME-GC-MS)The volatile components of fermented milk during storage were detected.The cholesterol scavenging ability of the strain in vitro was measured by ammonium ferric sulfate method,phthalaldehyde method and cholesterol oxidase method.The probiotics such as acid resistance and bile salt resistance,extracellular polysaccharide production,bile saline hydrolysis ability,bacteriostatic ability,cell surface hydrophobicity and antioxidant ability were studied by symmetrical parallel seed drops,anthracene sulfate method and plate streak method.The results:(1)the fermentation characteristics showed that the curdling time of strain DB-3 was shorter,only 8.44h;The acidity of curd is 71.95°T,and the acid production capacity is strong.The curd viscosity was 943.67m Pa.s,and the strain had excellent viscosity.Dehydration shrinkage was 32.43%,and water retention was strong.The content of free amino acid nitrogen in curd was5.27mmol/L,and the protein hydrolysis ability was strong,which was significantly better than other experimental strains.(2)Volatile components analysis results showed that the volatile components in the fermented milk of the two strains were mainly composed of acids,aldehydes,ketones,alcohols,esters and hydrocarbons,and the main flavor substances contained in the two strains included caproic acid,butyric acid,2,4-dimethyl benzaldehyde,2-nonone,n-octanol and other substances.Analysis showed that DB-3 fermented milk also contained high levels of acetaldehyde,2,3-butanedione,3-hydroxy-2-butanone,n-octanol,n-hexyl alcohol and other characteristic flavor compounds,among which the relative content of3-hydroxy-2-butanone was as high as 90.6%.These compounds increased the unique milk flavor and butterfat flavor on the basis of maintaining the fermented milk flavor.Improved the sensory quality of fermented milk;The JD-2fermented milk contains acetaldehyde,benzaldehyde,1-heptanol,high content of 2-heptanone and unique 6-methyl-5-heptene-2-one and other characteristic flavor substances,which provide fruit flavor and unique lemon aroma for the fermented milk.(3)cholesterol reduction ability results showed that the cholesterol clearance rate of the two strains measured by three methods was higher than25%;The viable bacteria count of JD-2 strain was(1.40±0.05)×10~6after 48h culture in the environment of gastric juice pH 3.0,and(1.31±0.10)×10~2after48h culture in the environment of intestinal bile salt concentration 0.3%.The content of extracellular polysaccharide was 54.23mg/L,which could make the strain have certain adhesion and play a probiotic role.The hydrophobicity reached 44.09%,belonging to the medium hydrophobic strain,with good adhesion characteristics.The strain had obvious inhibition on Staphylococcus aureus and Escherichia coli.(4)The results of antioxidant capacity showed that the DPPH scavenging rate of the fermentation broth supernatant of DB-3 and JD-2 strains was as high as 92.39%and 97.93%,and the supernatant of the fermentation broth of 3strains also had certain scavenging ability on superoxide anion,and the differences between DB-3 and JD-2 strains and the control strain 6047 were significant(P<0.05).The supernatant of fermentation broth of three strains of lactic acid bacteria also had certain reducing capacity for iron ion..(5)The results showed that the DB-3 strain can properly prolong the survival time of mice with anoxia tolerance at atmospheric pressure,and DB-3and JD-2 can properly prolong the survival time of mice with sodium nitritic poisoning.DB-3 has a certain role in improving the body’s anoxia tolerance.Conclusion:It is concluded that Lactobacillus delleri DB-3 has good fermentation characteristics and can produce volatile substances with characteristic flavor.It has a potential industrial application prospect as the starter culture of fermentation milk.The JD-2 strain of Lactobacillus deli has strong cholesterol-lowering and antioxidant capacity,which provides a theoretical basis for the development of functional dairy products.