Study On Lactic Acid Bacteria Fermentation Of Compound Fruit And Vegetable Juice

Lactic acid bacteria fermentation complex fruit and vegetable juice is the product of mixing fresh fruits and vegetables in a certain proportion,adding lactic acid bacteria to it and fermenting in a certain temperature for a certain period of time.The fermentation of fruit and vegetable can not only delay the shelf life of food,but also produce a variety of metabolites and bioactive substances,improve the nutrition and health function of fruit and vegetable juice,and improve the flavor of fermented fruit and vegetable juice.In this paper,strains with good fermentation performance were screened from natural fermented fruit and vegetable products,and the changes of functional substances,nutrients and flavor substances before and after fermentation were measured by using excellent strains to ferment compound fruit and vegetable juice.The main research contents and conclusions are as follows:1.Isolation and identification of excellent lactic acid bacteriaFifteen strains of lactic acid bacteria were isolated from solid-state natural fermentation and identified as Lactobacillus Plantarum(6 strains)and lactobacillus Paracei(1 strain)by 16S rDNA sequence analysis combined with physiological and biochemical characteristics,Lactobacillus Casei(6 strains),Lactobacillus Genus(2 strains).100%of the known sequences were selected for subsequent screening,which were recorded as S1,S2,S3,S4,S5 and S6,respectively.The growth curve,acid-producing,acid-resisting,salt-resisting ability and tolerance in artificial gastrointestinal juice were tested.The results showed that all 6 strains had excellent fermentation characteristics and could be used as fermentation strains of fruit and vegetable juice.2.Study on fermentation technology of compound lactic acid bacteria in fruit and vegetable juiceThe optimum proportion of mixed fruit and vegetable juice was determined by sensory evaluation and score:Strawberry:Tomato:carrot 3:2:5.The pH value,reducing sugar content,lactic acid content and total acid content were determined,the optimum strains for compound fruit and vegetable juice fermentation were identified as Lactobacillus Plantarum S3,Lactobacillus Casei S4 and Lactobacillus Paracesei S6.according to the above four indexes..The main fermentation parameters were determined as follows:Fermentation temperature 37?,60 h,and after fermentation temperature 15?,15 d.3.Changes of physical and chemical characteristics of lactic acid bacteria fermented compound fruit and vegetable juice.The results showed that the pH value,reducing sugar content and total sugar content of compound fruit and vegetable juice were significantly decreased,the total acid content and lactic acid content increased continuously in three periods.The results of HPLC showed that the contents of lactic acid,malic acid,citric acid and tartaric acid increased gradually,but the contents of oxalic acid,succinic acid and fumaric acid decreased until fumaric acid disappeared.The content of nitrite in fruit and vegetable juice at the end of fermentation met the national standard.The results of HPLC showed that there were only tryptamine and putrescine in fruit and vegetable juice before and after fermentation,and there was a significant difference(p<0.05).In addition,several antioxidant compounds were determined.The results showed that the content of total flavonoids decreased,and the content of total polyphenol decreased first and then stabilized.The activity of SOD increased at first and then decreased,but increased significantly(p<0.05).4.Flavor evaluation of compound fruit and vegetable juice fermented by lactic acid bacteria.Principal Component Analysis(PCA)and load analysis(EA)showed that there were significant differences between before and after fermentation,and the main fermentation period and post fermentation period could also be distinguished.The taste of mixed fruit and vegetable juice changed significantly before and after fermentation(p<0.05),but the taste of mixed fruit and vegetable juice did not change significantly during main fermentation and post fermentation.The volatile flavor components in fermented fruit and vegetable juice were determined by GC-MS.It was found that after fermentation,the kinds of volatile compounds were reduced,but after fermentation,a new kind of volatile compounds appeared,among them,aldehydes,acids,olefins and Furans increased continuously in the main fermentation and post-fermentation stages,while alcohols,ketones,esters and phenols retained most of the components with fruit aroma in the post-fermentation stage.