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Ohmic heating is an emerging thermal processing technology in which a food product is heated by supplying alternating current directly through it. In this study, grape juice was pasteurized at different voltage gradients (10, 20, 30 and 40 V/cm) from 20?C to temperatures of 55?C, 65?C, 75?C and 85?C for holding time 1, 3 and 5 min. Pasteurized juice samples were stored for 21 days at the refrigerated condition. System performance coefficient (SPC) of the ohmic heating system and the microbial properties of grape juice in terms of total plate count, mold count and yeast count were evaluated. It was observed that the temperature and heating rate of grape juice increased linearly with the voltage gradient. Total plate count, mold count and yeast count of grape juice greatly decreased with increase in voltage gradient, heating temperature and holding time. The microbial cells were destroyed due to electroporation which leads to pore-formation in the membrane and changes in cell permeability. After the storage period, microbial counts were found to be under the safe limit in the juice samples treated at 30 V/cm:85?C:5 min. SPC of the ohmic heating system was found in the range of 0.57-0.99. For effective pasteurization of juice at 85?C using 30 V/cm, SPC was 0.73, which was commendable. It is concluded that ohmic heating technology might be effectively used to pasteurize fruit juices with short processing time and it depends on applied voltage gradient, heating temperature and holding time. It is a pollution-free and high energy-efficient technology.
Ohmic heating, grape juice, microbial quality, system performance coefficient, electroporation
CSBE/SCGAB 2019 Annual Conference, Vancouver, BC, 14-17 July 2019.
Canadian Society for Bioengineering