Study On Fermentation Technology And Digestive Characteristics Of Compound Fruit And Vegetable Juice

The composite fruit and vegetable fermented juice,as a new kind of beverage,has a broad market prospect,and has become the hot spot of the research and development of domestic research institutes because of its healthy nutrition and various functions.In this paper,compound fruit and vegetable juice was prepared using Shanxi's characteristic fruits and vegetables as raw materials.Kefir grains and mixed lactic acid bacteria were added into the compound juice respectively for fermentation process optimization to obtain fermentation juice,and through the establishment of gastrointestinal digestion model,the effects of lactic acid fermentation and kefir grain fermentation on the digestive characteristics and antioxidant capacity of juice were compared and studied.Finally,HPLC was used to analyze the changes of organic acids in compound juice during fermentation,aims to provide theoretical basis for related fruit and vegetable fermentation product development.The results are as follows:1.In this experiment,mulberry,seabuckthorn,grape and carrot were used as raw materials to preparecomposite fruit and vegetable juice.Sensory score and polyphenol content were used as evaluation indexes to determine the composite proportion of juice through single factor and orthogonal test.The results showed that the optimum preparation technology of composite juice was 15% of mulberry,25% of grape juice,20% of carrot juice and 11% of seabuckthorn juice.Under this condition,the sensory score of the compound juice was as high as 93,the polyphenol content was 3.57mg/m L,which could be used for subsequent tests.2.Using compound fruit and vegetable juice as raw material,lactic acid bacteria mixed bacteria(Lactobacillus plantarum,Lactobacillus casei)and kefir grains were added to ferment the compound juice.Taking acidity and number of viable bacteria as indicators,the fermentation process was optimized through Box-Behnken experiment.Through regression analysisand practical feasibility,the optimum lactic acid fermentation parameters were determined as follows: Lactobacillus plantarum: Lactobacillus casei = 2:1,inoculation amount3.5%,fermentation time 34.6h and fermentation temperature 37?.under these conditions,the fermentation acidity of juice was 0.910% and the number of living bacteria was 9.35 log CFU/m L.Best kefir grains fermentation parameters as follows: inoculum amount 7.3%,fermentation time 41.7h and fermentation temperature32 ?.Under theconditions of this process,the fermentation acidity of juice was 0.837%,and the number of viable bacteria was 8.92 log CFU/m L.Compared with the pre-fermentation group,the contents of polyphenols and flavonoids were significantlyincreased,the antioxidant activity was significantly enhanced(p<0.05),and the kefir grains fermentation group was significantly better than the lactic acid fermentation group.3.The dynamic changes of functional components and antioxidant activity in juice before and after fermentation in lactic acid fermentation group and kefir grain fermentation group were studied by gastrointestinal digestion model,and the correlation analysis was carried out.The results showed that during the digestion process,compared with unfermented samples,the polyphenols and flavonoids content of fermented juice increased significantly,and the scavenging ability of DPPH,·OH and ABTS+ free radicals was further enhanced than before digestion,and the increase was the most significant during simulated gastric digestion(p<0.05).At the end of digestion,the clearance rates of DPPH,ABTS+,and ·OH in the kefir grain fermentation group were 10.1%,13.3%,and 6.5% higher than those in the lactic fermentation group,respectively,and 12.8%,14.7%,and 16.7% higher than those in the unfermented group.The flavonoid content was 1.07 and0.016 mg/m L higher than the lactic acid fermentation group,and 3.16 and0.022 mg/m L higher than the unfermented group.It is shown that the promotion effect of kefir grain fermentation is significantly better than that of lactic acid bacteria mixed bacteria,which has higher nutritional value and functional activity,and is more suitable for human digestive environment.4.Seven organic acids in lactic acid fermented juice and kefir grain fermented juice weredetermined by highperformance liquid chromatography.The results showed that before fermentation,malic acid,lactic acid,tartaric acid were the main organic acids of compound juice,and malic acid content was the highest,reaching 3818.90±22.26 mg/L.After fermentation,the main organic acids of the lactic acid fermentation group and kefir grain fermentation group were tartaric acid,lactic acid,acetic acid and malic acid,while oxalic acid,succinic acid,citric acid and so on were relatively few.The organic acid changes of the two groups were similar during the whole fermentation process: the content of malic acid,succinic acid and oxalic acid decreased significantly,the content of lactic acid,tartaric acid and acetic acid increased significantly(p<0.01),and the content of citric acid was not significant(p>0.05).