Study On Quality Changes Of Blueberry Juice By Ultra-high Pressure Treatment

Ultra high pressure processing(UHPP)and high-temperature processing(HTP)are two conventional technologics for sterilization of liquid food,As blueberry juice is sensitive to heat and temperature,we performed expeaiments on blueberry juice to investigate the effect of methods on juice quality,The microorganism and anthocyanin in blueberryjuice were measured after treatment under different conditions.To further investigate the effect of UHPP and HTP on the quality of blueberry juice,the PH,color and protein content variation at different pressure were also analyzed.The results were as follows:(1)Blueberry juice was treated under 100-500 MPa pressure and 80℃ for 6,12 and 24 min,after which the bacteria counts were determi-ned.The result indicated that higher pressure of treatment entailed more bacteria being killed,and 500 MPa was the optimal pressure for sterilization of blueberry juice,Longer time for treatment ensured better suppression of microorganism reproduction.Under the 400 MPa pressure,24 min was the best time for sterilization,and the remaining bacteria count was 3.87 CFU/mL,Increasing the time for HTP also improved the sterilization,but the heat would destroy the quality of blueberry juice.Therefore,considering both sterilization effect and quality preservation,UHPP was significantly superior to ETP.(2)In order to analyze the peroxidase(POD)change c aused by temperature and pressure,blueberryjuice was respectively treated at 80℃ and under the pressure varying from 100 to 500 MPa,The time for both treatments was 6,12 and 24 min.The POD residue was 19.00%after heat treatment at 80℃ for 6 min,and the POD was totally inactivated after 12 min,However,the POD in blueberry juice was activated under the condition of 100 MPa(6 min),200 MPa(6,12 and 24 min),300 MPa(6,12 and 24 min)or 400 MPa(6 and 12 min).The inactivation effect oeccurred only when the pressure reached 500 MPa,whose effect was actually inferior.The POD residue was 82.12%after 24 min under the 500 MPa.(3)The anthocyanin changes of blueberry juice under UHPP(100-500 MPa,6-30 min)and HTP(80s℃)treatment were analyzed.The result demonstrated that the anthocyanin remained in blueberry juice continuously decreased with the time of UHPP treatment,and the=decrease of anthocyanin was accelerated as the pressure was increased.When the pressure was below 500 MPa,the anthocyanin slightly decreased,but the change was not obvious,which is less than 3%after treatment for 30 min.However,the anthocyanin in blueberry juice was significantly reduced when the pressure reached 500 MPa.When the treatment time was the same,the damage of anthocyanin by UHPP was less than that by HTP.A kinetics model of degradation reaction was built and the result showed that the anthocyanin content was almost unchanged under relatively low pressure(≤200 MPa).Contrastively,the destroy to anthocyanin by HTP at 80℃ was much greater than UHPP.(4)The protein content,pH and color changes of blueberry juice after UHPP treatment under different conditions were also investigated.The protein content was 1.1 to 1.5 mg/mL after treatment,which was close to the untreated blueberry juice,indicating that UHPP had little effect on the protein content of blueberry juice.The pH-value was 3.23 to 3.42,which was not obviously changed,indicating that UHPP was also not influential to the pH value of Tolueberry juice.The color(ΔL,Δa and Δb)changed with the pressure,time and temperature of UHPP,but the change was not obvious to the naked eye.