Development And Functional Evaluation Of Blueberry And Wolfberry Fermented Fruit Juice

Blueberry and wolfberry not only contain a variety of nutrients and bioactive components,but also have antioxidant,relieve visual fatigue and other health functions.However,blueberry and wolfberry fruits are easy to rot,and lactic acid bacteria fermentation can not only retain their bioactive components,but also enhance their antioxidant capacity.Therefore,it is an effective fine processing method to develop them into fermented fruit and vegetable juice products.In this experiment,pectinase was used to hydrolyze the broken blueberry and wolfberry fruit,and the enzymatic hydrolysis process was optimized to improve the juice yield;then,lactic acid bacteria was used to ferment the blueberry and wolfberry enzymatic hydrolysate,and the fermentation substrate and fermentation process were optimized during the fermentation process;the blueberry and wolfberry fermented fruit juice was prepared by the above optimal process,and the fermentation conditions were monitored DPPH free radical scavenging capacity,total phenol content and total flavonoids content were measured before and after storage.Finally,stored them at 4 ~oC,20 ~oC and37 ~oC for 21 days.The specific research results are as follows:(1)Optimization of enzymatic hydrolysis of blueberry and wolfberry.Taking the juice yield as an indicator,the optimal enzymatic hydrolysis process of blueberry and wolfberry was obtained by single factor-orthogonal experiment as follows:enzymatic hydrolysis temperature is 55 ~oC,enzymatic hydrolysis is 3 h,enzymatic hydrolysis p H is 3.6,and pectinase addition is 0.2%.The sensory evaluation of the enzymatic hydrolysate was carried out,and its comprehensive evaluation score was 8.6±1.2.(2)Optimization of fermentation technology of blueberry and wolfberry.Firstly,the DPPH free radical scavenging ability and total phenol content were used as indicators to determine the proportion of mixed bacteria for fermentation:Lactobacillus rhamnosus:Lactobacillus plantarum volume ratio was 1:1;secondly,the fermentation substrate of blueberry and wolfberry was optimized by single factor orthogonal test as follows:4%glucose,2%yeast extract,3%inoculum.Finally,the fermentation process of blueberry wolfberry was optimized by single factor orthogonal test as follows:fermentation temperature was 39 ~oC,fermentation time was 30 h,and fermentation p H was5.0.The sensory evaluation of blueberry and wolfberry fermented fruit juice was conducted,and the comprehensive evaluation score was 7.2±1.0.(3)Changes in biologically active ingredients and antioxidant capacity before and after fermentation.The total phenol content is 1.40 times that before fermentation,the total flavonoid content is 1.18 times that before fermentation,and the DPPH free radical scavenging capacity is1.05 times that before fermentation.(4)Effects of different storage temperature on physical and chemical indexes,bioactive components and antioxidant capacity.The higher the storage temperature,the faster the p H value and the number of viable lactic acid bacteria decreased(P<0.05),and the lactic acid bacteria declined rapidly at 37 ~oC.The lower the storage temperature,the stronger the antioxidant capacity(P<0.05).The DPPH free radical scavenging capacity,ABTS free radical scavenging capacity,hydroxyl free radical scavenging capacity and metal ion scavenging capacity(ABS)at 4~oC were higher than those at 20 ~oC and 37 ~oC,and the free radical scavenging capacity were(92.83±0.24)%,(91.26±0.04)%,(36.11±0.41)%,and 0.350±0.004,respectively.Storage temperature had little effect on the content of flavonoids(P>0.05),which were 0.98±0.02 mg/m L,0.97±0.02 mg/m L and0.967±0.02 mg/m L at 4 ~oC,20 ~oC and 37 ~oC.Due to Maillard reaction during storage,the total phenol content in the sample was the highest at 20 ~oC,which was 2.76±0.03 mg/m L.The lower the storage temperature,the higher the activity of SOD(P<0.05).The activity of SOD in the sample was 456.57±4.38 U/m L at 4 ~oC.Finally,the sensory evaluation of blueberry and wolfberry fermented fruit juice stored at different temperatures showed that the highest score was 7.0±0.7 at 4 ~oC.In conclusion,the antioxidant capacity,bioactive components and good taste of samples stored at low temperature can be effectively preserved.