Ohmic and conventional drying of citrus products: energy efficiency, greenhouse gas emissions and nutritional properties

The use of energy efficient technologies for dehydration of food materials without compromising final food product quality is gaining increased interest in the food industry. A promising dehydration-enhancing process step that has been applied in the food industry mainly for pasteurisation operations is Ohmic heating. This study investigated the use of Ohmic and conventional thermal heating for dewatering of two citrus products, orange and grapefruit. A number of analyses including electrical thermal conductivity (ETC), energy consumption, cost, greenhouse gas (GHG) emissions, moisture content, PH and Vitamin C levels were performed. The results revealed that there was a positive increase of the ETC over time in both samples, resulting in higher values of 70⁰C for the orange samples and 100⁰C for the grapefruit samples. The moisture content of the samples was significantly (P<0.05) reduced during Ohmic and thermal dehydration over time while no significant difference was detected in terms of pH and Vitamin C level. The analysis of energy consumption showed that thermal dehydration was between 3.5 and 5 times higher than Ohmic dehydration. Similar trend was observed in terms of cost and GHG emissions.