Application of Electrical Heating Method for Grape Juice; Ohmic Heating

The application of current electrical heating processes is increasing with the developing technology. One of the current electrical heatingmethods as an alternative to the traditional heating process is Ohmic heating. Ohmic heating process is based on the heating principlethat depends on the heat generation in the product by passing alternating current from the solid / liquid substance. Ohmic heating isregarded as a particularly fast, homogeneous and efficient heating. In the present study, with the help of ohmic heating process (13 V /cm at constant voltage gradient), the grape juice is heated from 20 °C to 90 °C and kept at a constant temperature for 4 differentprocessing times (0, 20, 40 and 60 min.) It was aimed to examine some quality characteristics of grape juice. In addition, it was purposedto examine the electrical conductivity value, which is one of the important properties for ohmic heating during the process, and todetermine the total spent energy value for the waiting time at different constant temperature (90 °C). While the heating time of grapejuice from 20 °C to 90 °C was determined as 311 ± 5.01 s, it was stated that the temperature change due to time has a linear trend. Inaddition, it has been determined that as the temperature increases, the electrical conductivity value increases. It has been found that theelectrical conductivity value of grape juice during the heating process varies between 0.144-0.582 S / m. In addition, during the ohmicheating application, as the holding time increases, the total consumed energy value increases but the average power value decreases.The changes in some quality characteristics during the heating of grape juice and holding at constant temperature were investigated. Itwas determined that the amount of Total Phenolic Content (TFC), which is particularly sensitive to heat treatment, in grape juice duringthe heating and waiting periods was between 466-367 mg/L in terms of Galic acid equivalent. In addition, it was found that thehydroxymethylfurfural (HMF) content of grape juice was between 0.60-4.71 ppm depending on the process of holding at differentconstant temperature. As a result, it was concluted that it influences the TFC amount and HMF content, which are among the qualitycriteria, on the waiting time at 90 °C (p <0.05).