Ohmic Heating of Lemon and Grapefruit Juices Under Vacuum Pressure— Comparison of Electrical Conductivity and Heating Rate

Abstract

Ohmic heating fundamentally depends on electrical conductivity. In this study, grapefruit and lemon juices were ohmically heated under vacuum conditions. The electrical conductivity was measured at voltage gradients (10, 20, and 30 V/cm) and vacuum pressure (0 [atmospheric pressure], −30, and −60 kPa) for four temperature ranges (30, 40, 50, and 60 °C), meanwhile the heating rate was also reported at the same level of pressure and voltage gradient. The electrical conductivity and heating rate considerably vary by voltage gradient relative to pressure. Grapefruit had considerably lower electrical conductivity (about 20%) relative to lemon juice for the same pressure–voltage gradient treatment, while the percent reduction of heating rate (grapefruit relative to lemon) varied from 19 to 32%. The multivariate linear regression of electrical conductivity, including temperature and voltage, was found to be a more suitable model. pH assessments showed that pressure significantly affected the pH of grapefruit and lemon juices (P < 0.01). The combination of different treatments, which created a shorter residence time, caused a greater decrease in pH.

Effect of Ohmic Heating on the Rheological Characteristics and Electrical Conductivity of Mulberry (Morus nigra) Puree

“…A linear increase in electrical conductivity was observed following the temperature elevation during ohmic heating. The result obtained in this study was consistent with the previous studies which demonstrated that electrical conductivity of tomato concentrate increased linearly with the heating temperature as a result of reduced drag force of ionic compounds inside the product [Fadavi & Salari, 2019]. Electrical conductivity is affected by the ionic compounds of the product.…”

Thermal treatment alternatives for enzymes inactivation in fruit juices: Recent breakthroughs and advancements

“…Concerning the OH processing action mode, it is based on electromagnetic methods such as, i.e., radioactive dielectric, capacitive dielectric, radioactive magnetic, and inductive heating ones ( Fig. 2 ) [60] . Moreover, OH processing is similar, to some extent, to the microwave heating systems at different frequencies [61] .…”

“…2 Schematic diagram of the ohmic heating (OH) processing system; (1) power unit, (2) power analyzer, (3) computer, (4) thermocouple, (5) cell, (6) electrode, (7) glass dome, (8) vacuum pump, (9) buffer tank, (10) valve, (11) vacuum gauge, (12) needle valve. Adapted from Fadavi and Salari [60] with permission. …”

The influence of Ohmic‐vacuum heating on phenol, ascorbic acid and engineering factors of kiwifruit juice concentration process

“…The reason for the low electrical current passing through sample at OHVC can be attributed to the rate of bubbles expansion (Fadavi & Salari, 2019; Fadavi et al ., 2020). The effect of vacuum decreases the pressure difference inside and outside the bubbles; therefore, bubbles expansion will be more rapid and as a result their escape from the surface of media is facilitated, interrupting the passage of current through the sample (Fadavi & Salari, 2019). Also, it could be noted that the sample heat capacity and latent heat of vaporisation were a function of the pressure inside the heating chamber.…”