Studies On The Isolation,Identification Of Lactobacillus Plantarum Y-20 And The Antioxidant Activity Of Its Exopolysaccharides

Lactic acid bacteria(LAB)is a kind of bacteria which can produce large amounts of lactic acid by fermentable sugar.LAB can promote the growth of beneficial intestinal microorganisms and have certain effects on diarrhea,irritable bowel syndrome,allergy,lactose intolerance and irritation reaction.So it has important application value in industry,agriculture,medicine and other fields.The probiotic effects of many lactic acid bacteria are closely related to the exopolysaccharides produced.Exopolysaccharides(EPS)is a kind of polysaccharide compound secreted by some special microorganisms in the process of growth and metabolism,permeated into the culture medium and easily separated from the bacteria,which is of great significance to the growth of microorganisms.Chopped pepper is a traditional fermented vegetable.Its traditional processing method is to use the natural fermentation of lactic acid bacteria and processing of salt preservation.At present,the main lactic acid bacteria isolated from chopped pepper are L.plantarum,L.brevis,P.pentosaceus and so on.However,there are few reports on the study of exopolysaccharides produced by these lactic acid bacteria.In order to study whether there are lactic acid bacteria producing exopolysaccharides in chopped pepper,the strains of lactic acid bacteria with high exopolysaccharide production were isolated and screened from natural fermented chopped peppers in this study.The screened strains were identified by morphological observation,physiological and biochemical experiments,and molecular biology methods.The fermentation and extraction conditions of exopolysaccharides were optimized.And the antioxidant ability of crude polysaccharides was discussed.The results are as follows:(1)Isolation,screening and identification of exopolysaccharide-producing lactic acid bacteria.Five strains of lactic acid bacteria were isolated from natural fermented chopped pepper.After fermentation yoghurt test,screening of exopolysaccharides production,comparison of exopolysaccharides production and DPPH free radical scavenging ability test,a strain Y-20 with excellent characteristics was finally screened.Y-20 was identified as L.plantarum by physiological and biochemical tests combined with molecular biological identification.When the strain grew for 16 hours,the density of the strain reached the maximum(OD600nm=3.620),and the yield of exopolysaccharides was the highest(242.95 mg/L).(2)The fermentation conditions of exopolysaccharides production by L.plantarum Y-20 were optimized.The optimum fermentation conditions for exopolysaccharides production by L.plantarum Y-20 were determined by single factor experiments and orthogonal test,including different carbon,nitrogen sources,initial p H value of culture medium,culture temperature and inoculation amount.The optimum fermentation conditions were as follows: glucose and peptone were the best carbon and nitrogen sources,the optimum addition of glucose was 2%,the initial fermentation p H was 6.0,the fermentation temperature was 37?,and the inoculation volume was 3%.Under the optimum medium formulation and culture conditions,the exopolysaccharide produced by L.plantarum Y-20 was 322.55 mg/L,which was 54.12% higher than that before optimization(148 mg/L).(3)The extraction conditions and antioxidant activity of exopolysaccharides produced by L.plantarum Y-20 were studied.DPPH free radical scavenging ability,hydroxyl free radical scavenging ability,superoxide anion scavenging ability and total antioxidant ability were measured to evaluate in vitro antioxidant activity of EPS produced by L.plantarum Y-20.The results showed that the optimum addition of trichloroacetic acid was 10% of the final concentration of EPS,and the optimum addition of ethanol was triple fermentation broth when ethanol precipitated.The results of antioxidant test showed that the scavenging capacity of 1 mg/m L EPS to DPPH radical was equivalent to that of 2 ?g/m L Vc(about 20%)and 10 mg/m L EPS to hydroxyl radical was equivalent to that of 0.15 mg/m L Vc(about 55%).When the concentration of EPS was 10 mg/m L,the scavenging rate of EPS for superoxide anion(88.12%)was similar to that of 10 ?g/m L Vc(88.76%).The total antioxidant capacity of 4 mg/m L EPS(3.59±0.27 U/m L)was similar to that of 2 ?g/m L Vc(3.47±0.83 U/m L).