Study On Blueberry Juice Processing Technic

The blueberry juice was employed to analyze the effects on juice quality of juiceextraction by pectinase, clarification, concentrate and sterilization. The processingconditions were optimized and the changes of blueberry juice quality during storage werealso researched. The detailed contents and the main results were as follow:Response surface methodology (RSM) was employed to analyze the effects ofpectinase processing on juice yield, total anthocyanin content, total phenol content andtotal flavonoid content of blueberry juice. For resolving multi-response optimization,desirability function method was used to integrate juice yield, total anthocyanin content,total phenol content and total flavonoid content into a new target D (desirability value).The results showed that predicted regression models of juice yield, total anthocyanincontent, total phenol content, total flavonoid content and D value were found to be in goodagreement with experimental values (R2>0.92). The pectinase processing conditions hadsignificant effects on juice yield, total anthocyanin content, total phenol content, totalflavonoid content and D value of blueberry juice. The optimum conditions were: enzymedosage of0.6mg/g, hydrolysis temperature of51.6and hydrolysis time of2.36h. At thisoptimum point, juice yield, total anthocyanin content, total phenol content, total flavonoidcontent and D value were71.406%,420.367mg/L,2.784g/L,3.121g/L and0.9206,respectively.The blueberry juice was clarified respectively by bentonite, glutin and chitosan, andtheir effects on blueberry juice quality were analyzed. The results showed that after threeclarifications the juice light transmittances were all improved up. The bentonite had strongadsorption on anthocyanins, and the glutin could adsorb most phenols and someanthocyanins in blueberry juice. The most anthocyanins and phenols could remain in thejuice after chitosan clarification.The blueberry juice was concentrated respectively by microwave, rotary vacuum andatmospheric heating and their effects on blueberry juice quality were analyzed. The resultsshowed that rotary vacuum was the fastest concentrated process for blueberry juice. Allthese three concentrated processes had no effects on total phenol content, total flavonoidcontent and antioxidant activity. Most anthocyanins had been degraded after microwaveand atmospheric heating concentrate process, but with rotary vacuum process totalanthocyanin content had no loss.The first order reaction kinetics and Arrhenius equation was employed to analyze the effects of thermal and microwave sterilization treatment on total anthocyanins content,color and antioxidant activity of blueberry juice, and establish relative kinetics models. Theresults showed total anthocyanins content, color and antioxidant activity of thermal andmicrowave treated juice had significant loss, and all their changes accorded with the firstorder reaction kinetics(R2>0.94). Both thermal treated temperature and microwave treatedpower had significant effects on the rates of changes. With the increase of thermaltemperature or microwave power, the degradation rates of anthocyanins and color went upbut the degradation rates of antioxidant activity went down. Compared with thermaltreatment, microwave treatment could protect the anthocyanins and color of blueberry juice,but thermal treatment with high temperature could protect its antioxidant activity.The blueberry juice was stored in different temperatures to analyze the changes oftotal bacterial count, total anthocyanin content, color and antioxidant activity of blueberryjuice during storage. The first order reaction kinetics and Arrhenius equation was employedto establish kinetics models for total bacterial count, total anthocyanins content and color.The results showed that the total bacterial count, total anthocyanin content, color andantioxidant activity in thermal and microwave sterilization juice had both changedsignificantly. The changes of total bacterial count, total anthocyanins content and coloraccorded with the first order reaction kinetics (R2>0.9). The effects of storage temperaturewere significant on their rates of changes. With temperature going up, their rates ofchanges also went up. At a low storage temperature, total bacterial count increased slowlyand little loss was found in total anthocyanins and color, so the blueberry juice couldremain good quality for a long time. Compared with thermal sterilization juice,anthocyanins, color and antioxidant activity could remain better in microwave sterilizationjuice grew up a litter faster, but its quality guarantee period was shorter.