Optimization Of Fermentation Technology Of Blueberry Juice By Lactic Acid Bacteria And Effect Of Drying Method On Drying Effcet Of Blueberry Pomace

Blueberry fruit is rich in nutrition,sweet and sour,delicate and rich in phenols,dietary fiber and other nutrients.However,the lag of blueberry deep processing technology and the low utilization of by-products are the urgent problems to be solved in blueberry processing industry.Lactic acid bacteria fermentation can effectively improve the nutritional value and flavor of fruit and vegetable juice,and has probiotic effect.Therefore,the process of lactic acid bacteria fermentation of blueberry juice was studied,and the simulated in vitro digestion of fermented blueberry juice was studied.Finally,the drying technology of blueberry pomace produced by fermented blueberry juice was studied,in order to provide theoretical support for blueberry deep processing technology and improve the efficiency and productivity of blueberry fruit processing industry.In this study,the fermentation process of blueberry juice was optimized with lactic acid bacteria SH-470,the effects of fermentation on the quality and functional characteristics of blueberry juice were analyzed and compared,and the blueberry pomace was dried by different drying methods,and the effects of drying on its quality were analyzed.The main research contents and conclusions are as follows:(1)Taking the activity of superoxide dismutase(SOD)as the response value,the fermentation process of blueberry juice was optimized by response surface design on the basis of single factor experiment.It was determined that lactic acid bacteria SH-470 was suitable for the preparation of fermented blueberry juice.According to the optimization results and the actual situation,the optimal fermentation conditions were as follows:fermentation time of 24 h,fermentation temperature of 37°C,lactic acid bacteria inoculum amount of 0.1%,and sucrose addition amount of 6%.Under these conditions,the total phenol content in fermented blueberry juice was 413.40mg/L,anthocyanin content was 206.40 mg/L,antioxidant enzyme activity was 261.63U/m L,and the number of viable bacteria was 11.34 lg CFU/m L.(2)HPLC was used to detect the content of anthocyanin monomer in the fermentation process of blueberry juice.It was found that the species of anthocyanin monomer did not change,but the content changed significantly.The content of Malvidin-3-O-galactoside,the main component,increased significantly,and was59.59μg/m L after 24 h of fermentation,an increase of 16.87%compared with that before fermentation.(3)The changes of total phenols,total anthocyanins,viable lactic acid bacteria and antioxidant activity in blueberry juice at different fermentation stages were studied.The results showed that the digestion process would lead to the reduction of active substances in blueberry juice.After fermentation for 24 h,blueberry juice had the highest contents of total phenols and anthocyanins,243.71 mg/L and 66.29 mg/L respectively,which were significantly higher than those in the unfermented group(p<0.05).Some lactic acid bacteria still have vitality after digestion in vitro.Blueberry juice fermented for 24 h had the largest number of lactic acid bacteria after digestion,which was 6.16 lg CFU/m L.The test showed that lactic acid bacteria SH-470 had strong tolerance to artificial gastrointestinal fluid and can play a probiotic role in the gastrointestinal tract.(4)Blueberry pomace was dried by four drying methods:hot air drying(HAD),vacuum freeze drying(FD),vacuum microwave drying(MD)and vacuum freeze microwave drying(MFD).The effects of drying on the quality and antioxidant activity of blueberry pomace were analyzed.The micro morphological changes of dried pomace were observed by scanning electron microscope,and the changes of anthocyanin monomer in pomace before and after drying were detected by HPLC.Each drying method had little effect on the total sugar content in blueberry pomace.The contents of total phenol and total anthocyanin in blueberry pomace treated with MD were the highest,14.49 mg/g and 0.77 mg/g respectively.The scavenging ability of MD treated blueberry pomace to ABTS~+and DPPH free radicals was significantly higher than that of HAD(p<0.05).The main anthocyanin monomers in blueberry pomace are Malvidin-3-O-galactoside(901.31μg/g),Malvidin-3-o-glucoside(515.23μg/g)and Petunidin-3-O-galactoside(269.23μg/g).When FD,MD and MFD were used,the retention rate of single anthocyanin component in blueberry pomace was higher than that of HAD.