Ohmic heating assisted polyphenol oxidase inactivation of watermelon juice: Effects of the treatment on pH, lycopene, total phenolic content, and color of the juice.

Fresh watermelon juice was treated at 90 8C by hot-water (HW) and ohmic (OH) treatment (with
SS:316 electrodes) for 15, 30, 45 and 60 sec. PPO activity was reduced to 36.15 and 8.87% in 60
sec by HW and OH treatment respectively. The PPO inactivation was fitted to the first order
model; the reaction constant (k), D90 obtained was 0.02 s21, 115.1 sec, and 0.062 s21, 37.1 sec
for HW and OH treatment respectively. During both the treatments of watermelon juice total
phenols (TPC) showed significant change whereas no significant change was observed in lycopene
content. Total change in color (DE) during OH treatment was found lesser as compared to HW
treatment, hue angle was found to increase at a higher rate in HW than that of OH treatment.
Finally it was concluded that PPO of water melon juice can be inactivated rapidly by OH than HW
treatment.
Practical applications
Enzymatic browning and lycopene degradation are the major factors that limit the storage of
watermelon juice. High temperatures and processing times employed during thermal processing
cause deleterious changes in the color, flavor, and sensory aspects of the product. Therefore, this
study was conducted to investigate the comparative effect of ohmic and conventional heating on
inactivation of PPO as well as quality changes in watermelon juice so as to suggest a time-efficient
alternative that can be explored further for commercial packaging.