In this study, high voltage electric field (HVEF) was considered as a new system for thawing of ice pieces and frozen tuna fish. Firstly, the effects of distance between two neighbor needle electrodes (2.6, 5.2, 7.8 and 10.4cm) and the distance between needle and plate electrodes (3, 4.5 and 6cm) at a constant voltage of 12 kV on the thawing rate and required energy for melting of ice have been investigated. Results indicated that the application of voltage significantly increased melting rate and decreased energy consumption. The same effect was seen when the distance between neighboring needle electrode and the distance between needle and plate electrodes decreased. In the second phase, the effect of different electrode distances (3, 4.5 and 6 cm) and voltages on weight loss, protein solubility, lipid oxidation, texture, color, thawing time, and energy consumption and efficiency during fish thawing was evaluated. However, electrorostatic thawing increased energy consumption; thawing time and total volatile basic nitrogen decreased (TVBN). Production of ozone and negative ions of air under HVEF leads to the reduction of microbial load and hence, reduces TVBN of thawed fish during one week storage. On the other hand, HVEF has negative effect on the weight loss, protein denaturation, lipid stability and color of thawed tuna fish. Results indicated that the least damage to lipid and protein of fish obtained at lower voltages, and in these conditions, there was not significant difference between HVEF treatments and samples thawed at still air. Oxidation kinetics of vacuum-packed refrigerated samples during one week storage evaluated and rate constant was obtained. Enhancement of voltage and reduction of electrode gap diminished constant rate of lipid oxidation. Finally, thawing of fish was optimized by genetic algorithm. Optimization of both single and multiple methods were investigated. Multiple optimization, optimal voltage and electrode spacing was chosen on the basis of qualitative parameters. In the case of the optimal single thawing, voltage and electrode spacing was chosen based on the cost of energy in several countries. Key words : Tuna fish, Electrostatic thawing, Fat oxidation, Energy consumptio
