Study On The Optimization Of Fermatation Process Of Goji Juice By Combined Lactic Acid Bacteria And The Changes Of Nutritional Quality

Goji is a traditional medicinal and edible plant in my country,and its fruit is a bright ellipsoid-shaped berry.Goji contains a variety of functional ingredients,which have multiple functional activities such as anti-aging,immune regulation,and antiatherosclerosis.Hubei hybrid goji is produced by researchers who induced the Ningxia goji to double,and then crossed it with the local wild goji in Hubei.Compared with Ningxia goji,Hubei hybrid goji has a higher moisture content.The previous study found that it is not suitable for processing into traditional dried goji products.It is urgent to develop new processed goji products to improve the conversion rate of Hubei hybrid goji and the economic and social benefits of the industry.Using lactic acid bacteria to ferment characteristic fruits can not only give the product a unique flavor,but also transform or increase the types and content of active substances in it,and improve the nutritional value and health benefits of the product.However,there are research reports on the effect of lactic acid bacteria fermentation on the nutritional quality of goji juice less.Therefore,this article takes Hubei hybrid goji as the research object.Based on principal component analysis,a comprehensive evaluation of different lactic acid bacteria fermenting goji juice is carried out.On this basis,the lactic acid bacteria strains suitable for Hubei hybrid goji fermentation are selected for compound strain fermentation,and the fermentation process was optimized.To discuss the influence of lactic acid bacteria fermentation on the digestive characteristics of the gastrointestinal tract of goji juice,and analyze the changes in nutrients,volatile components and activity during the fermentation process,in order to provide experimental basis for the development of high value-added products.The main research contents and results are as follows:(1)Optimizing starter culture for goji juice fermentation based on principalcomponent analysisIn this study,the changes of physicochemical indexes,nutritional components and antioxidant activity of Goji juice fermented by six different lactic acid bacteria were compared.The results showed that the six kinds of lactic acid bacteria grew well in Goji juice.After fermentation for 48 h,the p H value of Goji juice decreased from 5.20 to 3.33-3.64.Among them,Lactobacillus plantarum and Streptococcus thermophilus had higher acid production capacity in Goji juice,and the total acid content reached 6.74 g/kg and 6.07g/kg,respectively.After fermentation with lactic acid bacteria,the content of total phenols and total flavonoids increased by 13.76% ? 28.07% and 55.80% ? 161.97% respectively.In addition,Lactobacillus casei and Lactobacillus fermentans significantly increased polysaccharide content in Goji juice(P<0.05).The DPPH free radical scavenging rate,total reducing power and ORAC activity of Goji juice were significantly increased by lactic acid bacteria fermentation,and the correlation analysis results showed that the antioxidant activity was significantly correlated with total phenols and total flavonoids(P<0.05).Based on the principal component analysis method,the quality of fermented goji juice with different strains was comprehensively evaluated.Lactobacillus plantarum and Lactobacillus fermentum are selected for compound fermentation on this basis.(2)Optimization of the fermentation process of goji juice with compound lactic acidbacteriaUsing the fuzzy comprehensive evaluation of total acid,total sugar,total phenol and total flavonoids as index,single-factor test and response surface optimization were carried out on the fermentation process conditions of goji juice,and the optimal fermentation process conditions were determined as follows: The compound ratio of Lactobacillus plantarum and Lactobacillus fermentans was 2:1,the inoculum amount is 4%,and the fermentation time is 54 h.Under these conditions,the total acid of fermented goji juice is9.12 g/kg,the total sugar is 15.23 mg/m L,and the total phenol is 311.15 ?g GAE/m L,total flavonoids is 36.00 ?g RE/m L.(3)Research on the characteristics of gastrointestinal digestion before and afterfermentation of goji juiceIn vitro simulated gastrointestinal digestion was performed on goji juice before and after fermentation.In the simulated gastric digestion environment in vitro,the content of total phenols and total flavonoids increased significantly,and the gastric digestion group>gastric acid group>gastric blank group,indicating that both pepsin and gastric acid can promote the release of polyphenols;in the process of intestinal digestion,The content of total phenols increased first and then decreased.The content of total flavonoids continued to decrease,but the intestinal digestion group> the intestinal blank group showed that pancreatin and bile had a certain effect on the release of total phenols and total flavonoids.Compared with the GJ group,the release of total phenols and total flavonoids in the FGJ group was significantly higher.After gastrointestinal digestion,the contents of total phenols and total flavonoids in the FGJ group were 1.48 and 2.02 times that of the GJ group,respectively.(4)Study on the changes of nutrient components and volatile substances during thefermentation of compound lactic acid bacteriaIn the fermentation process of the compound lactic acid bacteria,the sucrose,fructose and glucose in the goji juice are used as carbon sources for growth and reproduction,and a large amount of organic acids are produced.The content of lactic acid,acetic acid and ?-aminobutyric acid increases continuously during the fermentation process,while oxalic acid,malic acid and citric acid decreased significantly after fermentation(P<0.05).Fermentation of compound lactic acid bacteria can change the composition and content of phenolic substances in goji juice.Protocatechin,catechin,p-hydroxybenzoic acid,3-hydroxycinnamic acid,and myricetin increase significantly after fermentation,while vanillic acid and ferulic acid.The content of acid and p-coumaric acid was significantly reduced.Fermentation changed the composition and content of volatile components in goji juice.Among them,the content of alcohols,acids,and olefins increased,while the content of aldehydes and ketones decreased,and ethanol,1-hexanol,and linal were newly produced.Volatile components such as alcohol.(5)The effect of compound lactic acid bacteria fermentation on the antioxidant andantibacterial activities of goji juiceDuring the fermentation of compound lactic acid bacteria,the antioxidant activity of goji juice also continued to increase.After 54 hours of fermentation,the DPPH free radical scavenging capacity,total reducing power and oxidation free radical absorption capacity increased by 21.42%,14.18%,and 51.75%,respectively.Analysis shows that the increase in antioxidant activity may be closely related to the increase in the content of protocatechin,catechin,myricetin,and 3-hydroxycinnamic acid in goji juice.In addition,compared with the unfermented goji juice,the compound lactic acid bacteria fermentation also significantly improves the antibacterial performance of goji juice and increases the storage stability of the product.