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In the present study, the effectiveness of ohmic thawing (OT) on temperature distribution (TD) was evaluated by using a nondestructive measurement method: thermal imaging (TI). The effects of both OT process parameters and sample properties on TD of thawed minced beef were determined. Thermal images were taken from the central cross-sectional area of a thawed sample. In the first part of the study, the effects of OT system parameters (voltage gradient; 10-13-16 V/cm and electrode type; E1:titanium foil electrode with a smooth surface, E2: needled-type titanium electrode, E3: titanium electrode with pyramid surface shaped) and sample shape (X: 13 × 4 × 3 cm 3 ; Y: 13 × 6 × 2 cm 3 ; Z: 13 cm height × 3.91 cm diameter) were analyzed in detail. The best thawing condition (electrode type E2 and sample shape Y) was determined by taking into account of thawing time and TD properties obtained from a developed TI processing technique. In the second part of the study, the effects of OT process on TD properties of minced beef having different fat contents (2-10-18%) were compared with those of two different conventional thawing processes (stationary cold ambient + 4°C -RT and under cold running water + 4°C -WT). The percentage of thawed portions in central section was above 68% for OT and varied between 12 and 54% for CT. Rectangular-shaped samples had more homogeneous temperature distributions than cylindrical samples (p < 0.05). TI could be used to control the process by nondestructive monitoring of temperature during OT.

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Nowadays dietary habits of consumers have changed to more quick and easier but at the same time healthier meals. Therefore, ready-to-eat food production and home processing of such foods are gaining importance. Spinach is one of the main ingredients used in ready-to-eat baby foods, and it is produced in chopped, blanched, juice, and powder forms. Commonly ready-to-eat meals are sold frozen. Therefore, thawing process becomes an important processing step. Conventional thawing (CT) methods require a long process time and high-energy consumption. In the present study, frozen blanched spinach puree samples were thawed by ohmic thawing (OT) (10 V/cm, 15 V/cm). The thawing at 4 C (refrigerator thawing) was selected as the control thawing method. The energetic and exergetic evaluations were compared. Accordingly, thawing times were shortened by about 70-80% with OT. The energy loss during the CT method was higher than the OT method. The most energy-efficient (64.2% ± 4.0%) thawing condition was determined as 15 V/cm OT. In case of exergetic evaluation, the destroyed exergy value of the CT method was highest (19.0 ± 2.0 kJ) while those of thawed with 10 and 15 V/cm were 5.8 ± 0.7 and 3.8 ± 0.4 kJ, respectively. Similar to energetic efficiency, OT with 15 V/cm had the highest exergy efficiency value (40.5% ± 2.6%) while that of the CT method was 11.6% ± 1.0%. The result of the present study indicated that the OT process could be an alternative thawing method to CT to improve energy efficiency. Practical applications:As the ready-to-eat meal habit is becoming more common, processing of such foods is becoming more important. While preparing food, it is desired that the process to be done quickly, homogeneously, and efficiently. Usage of current food technologies to provide fast and homogeneous heating is becoming widespread. However, examining and evaluating their efficiency also emerges as an important issue. In this study, the use of OT, which is one of the current methods, for the thawing of spinach puree was investigated and the efficiency of OT in different voltage gradients was evaluated. In this way, it is thought that important data about the efficiency of the ohmic heating process, which utilization is increasing day-byday, during the thawing process are obtained. It is thought that these data will contribute to future studies and contribute to the widespread dissemination of OT.

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