Study On Ultrasonic And CO₂ Combined With Ultra-High Pressure Dynamic Pre-sterilization In Watermelon Juice

The relation between survivors of microorganisms and ultra-high pressure dynamic (UHPD) treatment to watermelon juice was investigated. The study of UHPD synergistic treatment was carried out to strengthen the effect of sterilization under the non-thermal treatments below:the ultrasonic, CO2 inert gases and ultra-high pressure (UHP) pre-sterilization.(1) Under the ultra high pressure dynamic, the pressure is inversely proportional to volume of bacterial survival and the high-pressure lethal curve of total colony complied with an order kinetics. Using the processing pressure 150MPa of homogenizer, the total plate counts of watermelon juice reduced to 2.1-2.3-log, the yeast and, mold reduce to2.0-2.3-log and the coliform bacteria reduce to 3.1-3.5-log.(2) It can enhance the pre-sterilize effect of high pressure dynamic combined with ultrasonic, CO2and UHP. Results showed that the total colony of watermelon juice reduced to about 2.7-log under ultrasonic frequency 100 KHz, ultrasonic time 15min and processing pressure 150MPa of homogenizer. The total colony reduced to 2.8-2.9-log with the add content of CO20.9-1.3 and pressure 150MPa of homogenizer. Two enhancement methods made the yeast and mold reduce to <20CFU/ml and the coliform bacteria reduce to<3 MPN/100ml. With the joint effects of 150MPa UHPD and 550MPa UHP,20min and 30℃, The bacillus aerobium reduced to 4.0-log.(3) It is less affected on the color, odor, taste and morphology of watermelon juice with direct high pressure dynamic and ultrasonic combined with the high pressure dynamic. CO2 combined with high pressure dynamic had a little influence on the evaluation sensory quality of watermelon juice.