Effects of Ohmic Heating on Denaturation of Whey Proteins Solutions: Influence on Whey-Derived Products Ricardo N. Pereira, António A. Vicente, José A. Teixeira IBB-Institute for Biotechnology and Bioengineering, Centre for Biological Engineering, University of Minho, Braga, Portugal (rpereira@deb.uminho.pt) ABSTRACT Ohmic heating is one of the earliest applications of electricity in thermal processing of food and is receiving increased attention because of its uniform heating of liquids with faster heating rates, which presumably enables obtaining products of a superior quality to those processed by conventional heating technologies. Given the biochemical structure of proteins, it is expectable that ohmic heating and its moderate electric fields will influence their properties and hence their behavior. The aim of this work was to evaluate the effects of moderate electric fields on denaturation and aggregation of whey proteins and its subsequent effects in whey-derived products. Results presented here show that ohmic heating led to lower whey protein denaturation at the early stages of heating, kinetically traduced by lower values of n and k, when compared to those from conventional heating (p < 0.05) under equivalent heating rate and holding times. Furthermore, whey protein aggregation (measured by dynamic light scattering in terms of aggregate size) was found to decrease with the presence of moderate electric fields applied during ohmic heating at 85 ºC, up to 30 min. Edible films prepared from ohmic heated film forming solutions present a decrease of water vapor permeability of 10%, when compared with films produced through conventional heating. Keywords: ohmic heating; whey proteins; denaturation, aggregation, edible films INTRODUCTION Thermal processing is believed to induce disruption of the native conformation of whey proteins, thus affecting their structure and functional properties of its derived products, such as whey protein isolate (WPI) and whey protein concentrate (WPC). Heating of WPI results in the exposure to the solvent of free sulphydryl groups (SH), normally occluded within β-Lactoglobulin (β-Lg) and bovine serum albumin (BSA), and hydrophobic amino acid side-chains [1]. SH may rapidly interchange with existing disulfide bonds to generate new inter- and intramolecular disulfide bonds [2]. During heating, the role of sulphydryl/disulfide interchange may promote intermolecular disulfide bond formation, which together with intermolecular protein–protein interactions (such as entropic forces, dipolar and electrostatic interactions) between unfolded “reactive” proteins, determines protein aggregation. Whey protein aggregation can produce a number of undesired effects such as formation of deposits on heat exchangers [3, 4] and gelling during the production of concentrated milks [5]. On the other hand, for the production of edible whey protein films the formation of aggregates in the film-forming solutions (before drying) is required to form stiff and stretchable films.[6]. Therefore, the knowledge of proteins behavior during heating is essential for the control of their properties and characteristics during the recovery and application of whey derived products [7]. Ohmic heating (OH) is receiving increased attention due to its uniform heating of liquids with faster heating rates, which enables obtaining products of a superior quality to those processed by conventional heating technologies [8-10]. This heating method involves the passage of an alternating electrical current through a food, which will heat due to internal energy dissipation according to Joule’s law. This technology offers great potential for use in a wide variety of food processing operations involving heat and mass transfer, such as blanching, evaporation, dehydration, fermentation [11], continuous cooking and sterilization of viscous and liquid food [12]. Given its volumetric heating, rapid heat penetration rates and also due to the presence of moderate electric fields, OH possibly influences denaturation and aggregation mechanisms of whey proteins, thus affecting WPI properties. However no experimental work has been reported to confirm this until the present moment. Therefore, the main objective of this study was to determine the levels of denaturation of whey proteins dispersions during ohmic heating and compare them with those obtained using a conventional heating