Effects of Vacuum and Juice Concentration on Electrical Conductivity by the Ohmic Method: a Case Study of Sour Cherry

Abstract

Electrical conductivity is a key parameter in ohmic heating. In this study, under vacuum conditions, sour cherry juice was concentrated up to 33% and 46.7% of the initial mass in order to have three levels of concentration. The samples were ohmically heated using three voltage gradients (10, 20, and 30 V/cm) under three pressure levels (atmospheric pressure and vacuum of − 30 and − 60 kPa). The dependence of electrical conductivity and heating rate on temperature, voltage gradient, and concentration was measured in the temperature range of (26.8 ± 0.3 °C, starting point) to (65.5 ± 0.6 °C) for all experiments. Compared with the pressure, the effect of juice concentration was more significant on the heating rate. A 60% reduction in the pressure resulted in an 11.3% drop in the heating rate, whereas a 46.7% change in the concentration led to a 30.7% decrease in the heating rate. The electrical conductivity decreased with increasing the concentration level and reducing the pressure (vacuum state). At a specific concentration, the multivariate linear regression models using temperature, pressure, and voltage gradient were found to be more accurate (R2 > 0.975).