Sugarcane juice was analyzed for the effect of four different time-temperatures (60-90°C for 5-20 min) at three electric field strengths (EFS) (24, 32, and 48 V cm -1 ) on PPO activity in a lab scale ohmic heater. At 608C, the activity decreased with increase in EFS while at 70-908C, increased activity was observed at 32 and 48 V cm21. Up to 97.8% reduction in activity was observed at 32 V cm -1 /908C/5 min. The biphasic model was the best to describe PPO inactivation kinetics. The kinetic analysis showed that the decimal reduction time (D-value, minute) decreased with increasing EFS at different temperatures. At 32 V cm-1/908C/5 min, the D-value was 8.25 and 76.55 min for labile and stable PPO fractions, respectively. The electric field sensitivity parameter (ZV-value, V cm -1 ) was lower at 60 and 708C but increased with treatment temperature. The z-value (z8C) for the labile fraction consistently decreased with increasing EFS and was lower than the stable fraction. Color change was inversely proportional to treatment temperatures at 24V cm -1 and directly proportional at 32 and 48V cm -1 . The kinetics for L, a, b values was best described by first order model while colour change was best explained by the combined model.
Practical applicationsSugarcane juice is one of the most widely relished beverages of south Asia. However, enzymatic browning is a major factor that limits its storage to only a few hours after extraction. High temperatures and processing times employed during thermal processing cause deleterious changes in the color, flavor and the overall nutritive components of the product. Ohmic heating has been applied to different commercial food products (like strawberries, grapes, orange juice) and has been rendered as a time-efficient process. Therefore, this study was conducted to investigate the effect of ohmic heating on inactivation of the browning enzyme (PPO) in sugarcane juice and its kinetic analysis, so as to suggest an alternative that can be explored further for commercial packaging of sugarcane juice. K E Y W O R D S D value, ohmic heating, PPO inactivation kinetics, sugarcane juice, Z value 1 | INTRODUCTION Sugarcane (Saccharum officinarum) is an exclusively cultivated crop in tropical and subtropical regions of the world. Fresh sugarcane juice is a popular beverage in many tropical countries and India is its second largest producer next to Brazil. Relished for its sweet taste and flavor, sugarcane juice is a great preventive and healing source for sore throat, cold, and flu (Khare et al., 2012). However, enzymatic browning is one of the major causes for deleterious changes in the sensory properties of the product thereby limiting its storage for a longer time (Bucheli and Robinson, 1994). Polyphenol oxidase (PPO) is one of the major enzymes responsible for browning. PPO catalyses the oxidation of monophenolic compounds to o-diphenols and o-dihydroxy compounds to o-quinones which causes browning (Jayaraman et al., 1982). To inhibit enzymatic browning, conventional methods like thermal pro...
