Article Effect of immersion ohmic heating on thawing rate and properties of frozen tuna fish Shahnaz Fattahi and Nafiseh Zamindar Abstract In the present study, the application of immersion ohmic heating was examined to improve thawing of frozen tuna fish cubes. The experimental tuna cubes (3  3  3 cm 3 ) were thawed under ohmic heating subjected to three different voltages (40, 50, and 60 V) with three different concentrations (0.3, 0.4, and 0.5% w/v) of brine solution. The parameters associated with the quality of tuna, such as thawing time, thawing rate, thawing loss, cooking and total losses, centrifugal loss, lipid oxidation, texture, and color, were investigated during ohmic heating thawing, and compared with the conventional still air thawing, water thawing at 27 and 40  C. The results showed that immersion ohmic thawing significantly decreased the thawing time of frozen tuna fish cubes. Thawing time in ohmic treatment (50 V- 0.3% brine) was 5.95 times shorter than conventional conditions. The lowest thawing and cooking losses were observed at ohmic treatments. In addition, the ohmic treatments (group 1) were evaluated versus conventional methods (group 2) and the results showed that thawing and total losses in group 1 were significantly lower than group 2. Keywords Tuna fish, immersion ohmic thawing, thawing, thawing rate, lipid oxidation, air thawing Date received: 30 May 2019; accepted: 30 October 2019 INTRODUCTION As a distinguished source of protein and unsaturated fatty acids, vitamins, and different nutrients, fish and its products play an important role in people’s diets (Khan et al., 2018; Li et al., 2017). Some countries relied on fish for above half of their animal protein consumption (Khan et al., 2018). Fish are the most extremely perish- able food products (Roiha et al., 2018) and their quality may be affected by many elements (Garcı´a et al., 2015). Maintenance techniques, especially cooling and freez- ing, minor the rate of spoilage while not exorbitant affecting the physical properties of the fish. If applied accurately, cooling and freezing can develop the shelf life in time ranges of several days to several months (Backi, 2017). The shelf life of fish is usually determined by microbial activity, nutritive value, appearance, tex- ture, flavor, and color. All of these variables are influenced by freezing, frozen storage, and thawing (Leygonie et al., 2012; Liu et al., 2017). It is almost difficult to cut good quality fillets out of a frozen fish and, consequently, a critical amount of heat has to be added to the fish to avert injury while filleting in (frac- tionally) frozen state. The amount of added heat must be adequate to thaw the inner of the fish block such that the phase convert of water from solid to liquid has just passed, or in other words, the amount of latent heat of fusion has been added to the fish piece (Backi, 2017) (temperature of the coldest spot being just above the product’s freezing point) (Llave et al., 2014). It must be declared that the freezing process runs quickly com- pared to the thawing process since frozen water is a better conductor of heat than liquid water. In thawing process, the exterior layers of the fish block operated Department of Food Science and Technology, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran Corresponding author: Nafiseh Zamindar, Department of Food Science and Technology, Isfahan (Khorasgan) Branch Islamic Azad University, Isfahan, Iran. Email: n.zamindar@khuisf.ac.ir Food Science and Technology International 0(0) 1–9 ! The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1082013219895884 journals.sagepub.com/home/fst