Process And Functional Properties Of Lactobacillus Plantrum Fermented Blueberry Juice

Blueberry,one of the five human health foods certified by FAO,is rich in polyphenols,anthocyanins and other nutritive active substances.It have been proved owned good preventive and inhibitory effects on oxidative damage caused by diseases such as cardiovascular diseases and cancer.Nevertheless,blueberry is ripened in summer and fresh blueberry is prone to rot during storage and transportation process.Lactic acid bacteria are widely used in food production due to their various probiotic functions.The excellent fermentation characteristics of lactic acid bacteria not only enhance flavor of fermentation substrate,but also effectively retain or even improve the functional quality of the fermentation substrate.Therefore,the research on the fermentation process of fermented blueberry juice can provide new ideas for blueberry deep processing technology and theoretical support for the fermentation law of fermented blueberry products.In this study,Lactobacillus plantarum J26,a strain of lactic acid bacteria suitable for blueberry juice fermentation,was selected as a fermentation strain from 13 strains of lactic acid bacteria.The environmental tolerance evaluation of L.plantarum J26 was carried out.Secondly,the fermentation substrate and fermentation process were optimized by single factor experiment and response surface experiment design.Then the basic indexes and nutritional functions before and after fermentation were tested to judge the fermentation process influences to blueberry matrix.Finally,the storage stability test was carried out.The results of this experiment are as follow:(1)Only two,L.plantarum J26 and L.casei TD062,of the 13 lactic acid bacteria could grow more than 1×107 cfu/m L.Due to the composition complexity of the blueberry juice,single fermentation strain is more conducive to the needs of subsequent research.Thus,L.plantarum J26 was selected as fermentation strain.Thereafter,the environmental tolerance of L.plantarum J26 was investigated,the results showed a strong resistance to acid,bile silt and Na Cl.It proved L.plantarum J26 is suitable for industrial application.(2)The growth of the strains evaluated by the colony count and the sensory evaluation from the four aspects of taste,odor,texture state and color were used as indicators for optimization of fermentation matrix and conditions.The results showed carbon source,6% glucose,and nitrogen source,3% skim milk powder,as supplement were the most suitable fermentation substrate.And the optimum fermentation process was 3% initial inoculation,fermentation temperature 37 o C and fermentation time 24 h.Under this condition,number of viable bacteria in blueberry juice after fermentation could reach more than 1×109cfu/m L,and the flavor was also delicious.(3)By colorimetric method,it was found the total amount of phenolic substances increased by43.42% after fermentation.Then HPLC detection of anthocyanins found that blueberry juice mainly contains four kinds of anthocyanins,including Cyanidin,Petunidin chloride,Pelargonidin and Peonidin.The total amount of anthocyanins increased by 15.38% after fermentation.Furthermore,the volatile components were analyzed by HSSPME-GC/MS,the volatile components increased from 21 to 29 after fermentation,and the types and contents of acid substances increased most obviously.The specific volatile components of the fermented blueberry juice were found to be acetic acid,butyric acid and methyl isobutyl ketone by principal component analysis.(4)The enzyme inhibitory ability and antioxidant capacity of blueberry juice were significantly enhanced after fermentation by L.plantarum J26.The inhibition of ?-glucosidase by blueberry juice was significantly enhanced,and the inhibition of ?-amylase was slightly improved,but there was no significant difference.The scavenging ability of DPPH,superoxide anion radical and hydroxyl radical three radicals and the mitigation ability of Caco-2 oxidative damage caused by H2O2 were also significantly enhanced after fermentation.(5)In vitro simulated digestion experiments showed that L.plantarum J26 can effectively tolerate the artificial gastrointestinal fluids.The results proved L.plantarum J26 effectively colonize the intestine and can be used as a starter to develop fermented products.Moreover,results also revealed that the phenols and anthocyanins in blueberry juice were mainly degraded in the intestine,and the degradation was significantly improved after fermentation which confirmed L.plantarum J26 could promote the degradation of functional substances of blueberry juice in gastrointestinal fluid.(6)The results of storage stability test showed that the p H value of blueberry juice decreased continuously during the storage period,and the total acidity increased continuously.The number of viable bacteria decreased with the storage time,but the number of viable bacteria remained above107 cfu/m L.Nevertheless,total amount of phenolic substances and the anthocyanins decreased obviously.Above all,the fermented blueberry juice was stable during the 4 weeks storage period.