The use of ohmic heating in processing of food industry GIANPIERO PATARO a* , GIORGIO DONSI’ b,c , GIOVANNA FERRARI a,c a)Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132 - 84084 - Fisciano (SA), ITALY (b)Department of Computer Science, University of Salerno, Via Giovanni Paolo II, 132 - 84084 - Fisciano (SA), ITALY, (c)ProdAl scarl, Via Ponte don Melillo - 84084 - Fisciano (SA), ITALY gpataro@unisa.it ; http://www.unisa.it ; http://www.prodalricerche.it Abstract: - The aim of this work was to identify optimal pre-treatment conditions for cannellini beans in order to improve heating uniformity and, thus, the quality of product, during the subsequant sterilization process. Dry beans were blanched for different length of times (35 and 50 s) in a water bath set at 90°C after soaking (12 h) in tap water. Heating curves of solid-liquid mixtures (53g of beans/100g of mixture) of pre-treated beans and salt solution (1 g/100mL) were determined in a static ohmic heating device by applying a constant voltage of 100V. Results showed that the ohmic heating rate of beans increased with increasing the blanching time as a direct result of the increase of electrical conductivity. Optimal pre-treatment conditions, which allowed the ohmic heating of both phases of solid-liquid mixture at comparable rate, were found when beans were blanched for 50 s at 90°C. Beans pre-treated under optimal blanching conditions and sodium chloride solution (1g/100ml) (53g of beans/100g of mixture) were then subjected to both ohmic and in-container sterilization process. The solid-liquid mixture was sterilized at 121 °C for 10, 15 and 20 min. The parameters measured immediately before and after thermal treatments were: total microbial count, yeasts and molds, split degree, and proteins content. The experimental results have shown that, regardless the thermal method and treatment conditions the initial microbial spoilage was reduced up to below the detection limit of the method (<10 cfu/ml). When compared to the beans sterilized by conventional treatment, the samples treated by the ohmic method appeared of attractive appearance, with a lower split degree. The analyses of the chemical composition revealed a higher proteins concentration in sample processed by ohmic heating than those treated by conventional method. Key-Words: - Ohmic heating, In-container sterilization, Cannellini beans, Heating uniformity Microbiological stability, Quality parameters. 1 Introduction Traditional thermal preservation processes such as in-container sterilization or continuous flow aseptic processing of food products, are widely used in food industry to deliver shelf-stable food at ambient temperature [1]. However, because this methods rely on indirect mechanisms of heat transfer to food products, the overall quality of stabilized foods is typically poor, especially when fluids containing large particulates and fluids of high viscosity are processed [2]. Due to these drawbacks, the use of direct heating through a Joule effect, such as ohmic heating, has gained increased attention in the food industry. Ohmic heating is distinguished from other electrical heating methods either by the presence of electrodes in direct contact with the food (as opposed to microwave and inductive heating, where electrodes are absent) or by the frequencies and waveforms used. In a ohmic heating processing, the food material (liquid, solid or particulate-liquid mixture) placed between the two electrodes of a ohmic heater acts as part of the electric circuit through which electric current (usually alternating) fed by a power supply flows. The heating occurs in the form of internal energy transformation (from electric to thermal) within the material as a result of its inherent electrical resistance [2]. Interestingly, in liquid-particulate food mixtures, ohmic processing enables, under certain circumstances, large particulate and carrier fluids to heat at comparable rates, increasing the final product quality and adding value to products [3]. This very desirable scenario, which is hardly achieved during conventional heating of solid-liquid mixture, depends on the relative conductivities of the system’s phases and the volume fractions of the respective phases [2]. Solids of low conductivity compared to liquid will lag behind if they are in low Latest Trends in Applied and Theoretical Mechanics ISBN: 978-960-474-377-3 102