Enhanced inactivation of pectin methylesterase in passion fruit juice by ohmic heating

This study investigated the effectiveness of ohmic heating (OH) for the inactivation of pectin methylesterase (PME) in passion fruit juice. PME is a heat-resistant enzyme responsible for juice cloud loss and quality deterioration during storage and is therefore commonly used as an indicator of pasteurisation efficiency. Juice samples were initially heated from 20 to 70 °C and subsequently held at 70 °C for 10 s while being subjected to different electric field strengths (20-40 V.cm-1) and frequencies ranging from 50 to 10 000 Hz. The highest PME inactivation was observed at 60 Hz, and increasing electric field strength further enhanced the inactivation effect. Based on these results, a frequency of 60 Hz and an electric field strength of 30 V.cm-1 were selected for subsequent experiments. The effects of temperature (60-90 °C) and holding time (0-90 s) on PME inactivation during OH treatment were then evaluated and compared with conventional heating (CH). OH treatment at 90 °C for 70 s resulted in approximately 90% PME inactivation, which was 10.2% higher than that achieved by CH. In addition, OH treatment caused no significant additional degradation of ascorbic acid, total polyphenols, or antioxidant activity, indicating that the applied electric field did not adversely affect these bioactive compounds. These findings demonstrate that ohmic heating is a promising and mild pasteurisation technology for fruit juice processing.