Development of an Economic and Portable Ohmic Heater Using RSM and ANN Statistical Models and Validating Its Performance for Preserving Nourished Moringa Leaves

Abstract

Ohmic heating is a thermal method of preserving food that uses electric current to produce high-quality food products with minimum sensory, nutritional, and structural changes. In this study, we developed an affordable and portable ohmic heater by statistically modeling its volumetric heating profile. We evaluated the performance by blanching Moringa oleifera (Moringa) leaves, a beneficial tree with significant nutritional and medicinal properties in its various parts. The fabricated heater functioned with a 60 Hz frequency and an AC electric source for the voltage supply. Five digital thermometers recorded the uniform temperature at different positions of the ohmic chamber every 30 s for 180 s, and the temperature profile was modeled using two statistical models, namely, the response surface method in Design Expert 7.0 and an artificial neural network in MATLAB 15.0 software. Uniform volumetric heating was confirmed empirically at the combination of four voltage gradients (10, 15, 20, and 25 V/cm) with three sodium salt concentrations (0.5%, 1.0%, and 1.5%) as food probes. The predicted heating parameters from statistical models were then employed to blanch Moringa leaves for extended storage. The nutritional properties of ohmic-blanched Moringa leaves were compared with the fresh and steam-blanched samples. The ohmic-blanched leaves were found to retain nutrients substantially higher compared to the steam-blanched leaves. The carbohydrate, protein, ascorbic acid, carotenoid, phenol, flavonoid, and iron content in ohmic-blanched leaves were found to be 14.6 ± 1.67 g/100 g, 6.3 ± 0.2 g/100 g, 135.07 ± 1.35 mg/100 g, 95.43 ± 1.4 mg/g, 37 ± 1 mg GAE/g, 28.03 ± 1.64 mg QE/g, and 15.1 ± 0.26 mg/g, respectively. Further, the carbohydrate, flavonoid, and iron content were higher in the ohmic-blanched sample than in the fresh leaves. Overall, our findings indicate that small-scale industries and homemakers could use the ohmic heater we fabricated to effectively preserve Moringa leaves, particularly food materials, retaining their nutritional values.