The effects of field strength and multiple thermal treatments on electrical conductivity of strawberry products were investigated. Electrical conductivity increased with temperature for all the products and conditions tested following linear relations. Electrical conductivity was found to depend on the strawberry-based product. An increase of electrical conductivity with field strength was obvious for two strawberry pulps and strawberry filling but not for strawberry topping or strawberry-apple sauce. Thermal treatments caused visible changes (a decrease) in electrical conductivity values of both strawberry pulps tested, but the use of a conventional or ohmic pre-treatment induces a different behavior of the pulps' conductivity values. Ascorbic acid degradation followed first order kinetics for both conventional and ohmic heating treatments and the kinetic constants obtained were in the range of the values reported in the literature for other food systems. The presence of an electric field does not affect ascorbic acid degradation. ᮊ Industrial relevance: Due to the ability of the ohmic heating technologies to achieve rapid and reasonably uniform heating of electrically conductive materials its impact on food quality is of interest. This study shows interesting relationships between heat treatment and electrical conductivity of strawberry pulps and also suggested the product dependency for optimum ohmic heating applications.

The effects of field strength, soluble solids (from 14 to 59.5 °Brix) and particle size (using two size distributions) on electrical conductivity were investigated. Electrical conductivity increased with temperature for all the products and conditions tested following linear or quadratic relations. Electrical conductivity was found to vary greatly between strawberry‐based products. an increase of electrical conductivity with field strength was obvious for fresh strawberries and strawberry jelly but not for strawberry pulp, probably due to the presence of texturizing agents. This parameter decreases with the increase of solids and sugar content. For some of the formulations tested (solid content over 20% w/w and over 40 °Brix) a different design of ohmic heater may be necessary because of the low values of electrical conductivity.

A critical issue in the modeling of ohmic heating of solid-liquid mixtures is the understanding of worst-case scenarios, and in particular, the reliability of mathematical models under such conditions. This study involves examination of two alternative published formulations, one involving the use of circuit theory and a well-mixed fluid assumption, against another formulation, involving the solution to Laplace's equation, but without convective effects. As apected, the models (and an analytical solution) yield identical results under situations where solid andfluid electrical conductivity are equal. However, when the solid is of lower electrical conductivity than the fluid, the Circuit Analogy, Mixed Fluid ( C M F ) approach is shown to be more conservative than the Laplace Equation,No Convection (LENC) approach. This prediction is borne out by experimental studies, which confirm that the worst-case scenario in ohmic heating is not necessarily associated with a stationary fluid situation. Under the less likely conditions where the solid is more conductive than the fluid, the LENC approach is more conservative than the CAMF approach. Models are also compared with respect to other features, such as practicality of use, and computational cost.

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