Ohmic heating of strawberry products: electrical conductivity measurements and ascorbic acid degradation kinetics

Abstract

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 process of producing tomato paste by ohmic heating method

“…There are several published patents about the usage of ohmic treatments on several food materials such as; strawberry (Allali et al (2008); Sarang et al (2008); Castro et al (2004)); red apple, golden apple, peach, pear and pineapple ); tomato soup (Jun and Sastry (2005)); apricot and peach purees Icier and Ilicali (2005a)); sour cherry juice (Icier Icier and Ilicali (2004)); tylose (Icier and Ilicali (2005b)); seawater (Assiry et al (2010a); Assiry (2011)); lemon juice (Darvishi et al (2011)); milk (Stancl and Zitny. 2010;Bansal and Chen.…”

Ohmic Heating Behavior of Certain Selected Liquid Food Materials

“…They reported that the temperature affected the electrical conductivity values of fresh orange juice, but the relationships were not given. Castro et al (2004) studied the effect of electrical field strength during ohmic heating of strawberry products. Ohmic heating is currently being used for the processing of whole fruits in Japan and the United Kingdom (Sastry & Barach, 2000).…”

Temperature dependent electrical conductivities of fruit purees during ohmic heating

“…They reported that the temperature affected the electrical conductivity values of fresh orange juice, but the relationships were not given. Castro, Teixeira, Salengke, Sastry, and Vicente (2003) discussed the effect of temperature and sugar content on the electrical conductivity values of strawberry based products whereas Castro, Teixeira, Salengke, Sastry, and Vicente (2004) studied the effect of electrical field strength. Ohmic heating is currently being used for the processing of whole fruits in Japan and the United Kingdom (Sastry & Barach, 2000), for production of syruped fruit-salad and fruit juices (Anonymous, 2002).…”

“…The data on the electrical conductivity changes of fruit purees during ohmic heating is very important in designing ohmic heating systems to be used in baby food lines. Castro et al (2004) mentioned that it was important to evaluate the electrical properties of a food intended to be processed by ohmic heating by clearly demonstrating the significant differences of electrical conductivity between the several products tested.…”