Ohmic heating assisted vacuum evaporation chamber: Finite element analysis and evaluation of parameters for processing of amla juice

Conventional thermal processing in food industries incurs a high energy demand while causing nutritional degradation at higher temperatures. The present study aims to design, build, and validate a novel, energy-efficient, pilot-scale vacuum-assisted ohmic heating evaporation (OHVE) system for the thermal processing of liquid foods. Concentric stainless steel – 316-grade electrodes were housed inside a main cylinder (190 mm x 600 mm) for the treatment of 3 L of liquid food material. The structural and commercial viability of the system was simulated for pressure load conditions using the Finite Element Analysis (FEA) technique coupled with a mesh convergence study. The results from FEA suggested that for a 10 mm mesh size and 2 mm thick stainless steel − 316 shell, maximum von Mises’ stress was observed (90.84 MPa) at the top cap of the vessel providing for an acceptable factor of safety of 2.25. The simulated results were further numerically validated and a 3 % difference in the values was observed, highlighting the accuracy of the model. When amla juice was processed inside the developed system, a linear behavior of electrical conductivity was observed from 17- 59 °C which varied between 0.31 and 0.63 S/m. The equipment provided rapid heating rates (0.7 to 3.08 °C/min) and high system performance coefficients (0.81 to 0.90) at different voltage gradients (7.5 – 12.5 V/cm). The effect of OHVE process was further studied on the physiochemical properties of treated amla juice for the first time, by varying voltage gradient (7.5 – 12.5 V/cm), temperature (65 – 75 °C), and time (0.5 – 1.5 h). The results suggested that the highest quality reduction was observed at 10 V/cm, 75 °C, and 1.5 h witnessing up to a 32 % and 30 % reduction in ascorbic acid and total phenols, respectively. On the other hand, water removal rate varied between 1.83 to 2.89 mL/min while a non-significant effect on the pH of juice was observed. Subject to further validation of the developed system, the findings of the present study could enhance the commercial applications of the ohmic heating technology to provide high-quality thermally processed food products.