Screening Of Autochthonous Lactic Acid Bacteria From Fruit Sources And Fermentation Characteristics In Blueberry Juice

Blueberries are rich in organic acids,vitamins,minerals,anthocyanins,phenolic acids,flavonols.Most notably,blueberries have many functionalities such as scavenging free radicals,antibacterial,anti-inflammatory,and protecting eyesight.Blueberries can be used as good fermentation substrates for lactic acid bacteria.However,it is not mature for the blueberry juice fermented with lactic acid bacteria in industrial scales due to some drawbacks such as poor growth ability of lactic acid bacteria in low p H juice environment,inhibition by blueberry polyphenols and unclear metabolic mechanism.Therefore,it is very necessary to select the special lactic acid bacteria strains suitable for fermented blueberry juice.The lactic acid bacteria which can grow and metabolize well in acidic juice system were firstly isolated from different fruits,and then fitted the lactic acid bacteria fermentation kinetic equation with the number of viable bacteria,p H change,and lactic acid production as indicators to study the bacteria fermentation characteristics.And through the determination of anthocyanins,phenolic acids,flavonols,organic acids,and antioxidant activities in blueberry juice,explore the effects of lactic acid bacteria fermentation on the composition and physiological functions of blueberry juice.And 1 strain of Lactobacillus plantarum LSJ-TY-HYB-T7 and 1 strain of Lactobacillus fermentum LSJ-TY-HYB-L16 compound fermented blueberry juice were screened to reveal the effect of mixed fermentation on the functional characteristics of blueberry juice.The storage stability of fermented blueberry juice was also studied,which provided a certain technical basis and theoretical reference for the development of new fermented juice products.The research results are as follows:(1)Nine strains of lactic acid bacteria which can be used to ferment blueberry juice were selected from blueberry,blackberry,cherry,cherry tomato and apple.After 48-h fermentation,the number of viable bacteria in blueberry juice fermented with isolated strains was higher than higher than 10 Log CFU/m L.In addition,the p H value decreased over 11.5%.The content of malic acid declined over 71.4%.And the content of lactic acid was higher than 2351.07mg/L after 48-h fermentation.(2)These isolated autochthonous lactic acid bacteria from fruit environment also showed a strong ability to promote the conversion of phenolic substances and enhance the antioxidant activity of blueberry juice.The lactic acid bacteria significantly changed the distribution of organic acids and phenolic components in blueberry juice.The results showed that the probiotic fermentation of Lactobacillus plantarum and Lactobacillus fermentum resulted in a decrease in quinic acid,malic acid and citric acid while an increase in the content of shikimic acid and lactic acid.The anthocyanin content was significantly reduced in the late fermentation period.As a result,the retention rate of anthocyaninswas all above 50% after fermentation.Among all the phenolic components,the content of gallic acid,chlorogenic acid,rutin,myricetin and quercetin-3-rhamnoside were significantly increased after 48-hours of fermentation,while the content of delphinium-3-glucoside,paeoniflorin-3-glucoside,malvin-3-arabinoside and p-hydroxybenzoic acid were significantly decreased.The samples fermented by LSJ-TY-HYB-L16 had the strongest antioxidant activity,which the ABTS free radical scavenging ability and iron ion reduction ability improved by 97.4% and 107.8%,respectively.Lactobacillus plantarum LSJ-TY-HYB-T7 、 LSJ-TY-HYB-T9 and Lactobacillus fermentum LSJ-TY-HYB-C22 、LSJ-TY-HYB-L16 can be used as representative lactic acid bacteria strains for blueberry juice fermentation.(3)Mixed bacteria fermentation can significantly increase the total phenolic content and antioxidant activity of blueberry juice,and improve the flavor of the juice.The mixed bacteria inoculation amount of Lactobacillus fermentum LSJ-TY-HYB-L16 and Lactobacillus plantarum LSJ-TY-HYB-T7 was 0.5%: 0.5%.Compared with single bacteria fermentation,blueberry juice fermented with Lactobacillus plantarum LSJ-TY-HYB-T7 and Lactobacillus fermentum LSJ-TY-HYB-L16 compound could increase the total phenolic contents,which was 61.1% higher than that before fermentation.The mixed bacteria fermentation has better performance on the improvement of antioxidant activity,therefore,it possessed the highest ABTS free radical scavenging ability and iron ion reduction ability.In addition,GC-IMS analyzed the volatile ingredients of blueberry juice,and showed that the volatile substances of mixed bacteria fermented blueberry juice contained volatile substances of LSJ-TY-HYB-L16 and LSJ-TY-HYB-T7,and had higher concentration of esters,improving the flavor of fruit juice.(4)The blueberry juice fermented with the autochthonous lactic acid bacteria from fruits can enhance the storage stability and extend the shelf life.Blueberry juice fermented with individual Lactobacillus plantarum LSJ-TY-HYB-L16,individual Lactobacillus fermentum LSJ-TY-HYB-T7 and their combination were stored at 4 o C for 60 days.It was found that the physical and chemical quality indexes and microbial indexes met the national standards.The number of viable bacteria exceeded 7 Log CFU/m L in the end of storage.Moreover,the juices fermented by mixed bacteria strains had higher number of viable bacteria(more than 8 Log CFU/m L)than the counterparts fermented by each individual strain,and the sensory quality was significantly better than other products.