Comparative evaluation of ohmic and conventional heat treatment on process time, microbial quality and bioactive retention of citrus beverages

Abstract

Ohmic heating of sweet orange processed products (unsweetened juice, ready-to-serve (RTS) beverage, nectar, squash) was carried out with five different electric field strength ranging from 8 to 16 V/cm for comparing the impact of ohmic and conventional heating on their microbial load and physico-chemical properties. Pasteurization of products was achieved through ohmic heating (at 90 °C with holding time 1 min). Results indicated that electrical conductivity (EC) and high electric field intensity had positive effect on reduction of processing time of citrus beverages. EC reduced upon addition of sugar and dilution of juice in the products, hence no current flow was observed in RTS irrespective of voltage applied. In rest of the three products, more than 50 % reduction in microbial population was observed after processing at high voltage (210 and 240 V). Across the samples, ohmic process proved to be better for retention of total antioxidant activity, total phenolic content, flavonoids and ascorbic acid in comparison to conventional process. Energy consumption was high in squash and nectar due to low EC. Higher ohmic voltage given for pasteurization reduced the enzyme activity by 41.66 % in nectar. Shortened process time for ohmically treated citrus beverages resulted in least change of sensory attributes which were similar to control. Ohmic heating at high voltage treatment (more than 210 V) was best to reduce process time of citrus unsweetened juice. Overall product quality was more acceptable in ohmic treated sample as compared to conventionally heated ones.