Rapid Pasteurization of Apple Juice Using a New Ultrasonic Reactor

摘要

A new ultrasonic reactor was used to rapidly inactivate and in apple juice. It was found that high pulp content made ultrasound less lethal to , while it had no significant effect on . When the pulp free apple juice was ultrasonically processed, the 5-log reduction time was 35 s for at 60 °C and 30 s for at 62 °C. Ultrasound treatment had no significant effect on antioxidant activity determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, but it significantly increased the total phenolic content. The treatment also resulted in more stable juice with higher uniformity. During 28 d of storage at 4 °C, the total plate count in apple juice ultrasonically treated at 60 °C for 35 s remained around 1.00 log CFU/mL, whereas it was nearly zero for a stronger ultrasound treatment at 62 °C for 30 s. These values were much lower than those in the untreated one, which increased from 3.65 log CFU/mL to 8.36 log CFU/mL during the storage. At the end of the storage, the control and thermally treated apple juice lost almost 70% of antioxidant activity, whereas the ultrasonically treated juice only lost 20–40%.