Effects of different sterilization methods on microorganisms and quality of clarified mixed pear juice

Effective sterilization method is a crucial step to ensure the safety of juice and extend its shelf life. In this study, the effects of four sterilization methods, including pasteurization, microwave, ultrasonic and ultra-high-pressure sterilization on microorganisms and quality of clarified mixed pear juice (mixture of Xinli No.7 and Nanguo pear juice) were investigated. The results showed that the microbial quantity in pear juice was significantly(P < 0.05) reduced by sterilization methods. After pasteurization, the sugar-acid ratio was significantly(P < 0.05) increased. The browning degree of pear juice treated by microwave was the lowest and the transmittance was the highest among all sterilization methods. The ascorbic acid content of pear juice was significantly(P < 0.05) increased by ultrasonic treatment, while the content of total soluble solid, soluble sugar, total acid, and total flavonoids contents were increased ultra-high-pressure sterilized-pear juice. Moreover, ultrasonic and ultra-high-pressure treatments obtained the highest retention rate of volatile compounds in pear juice among four sterilization methods. Conclusively, compared with other sterilization methods, ultra-high-pressure sterilization seemed to be the most effective method to maintain the quality, nutritional values and flavour of mixed pear juice.