In order to investigate the applicability of ohmic heating in the blanching and heat sterilization process of vegetable foods, various electrical properties and heating characteristics were studied using intact potato. The electrical conductivity of potato with cell structure was 0.025 S/m, which was lower than that of starch and protein gel, and was increased linearly with increasing temperature. The temperature of ohmic heating was sharply increased from 8 min at 60 V, reaching 90°C after 10 min. The temperature rise was rapid at 60°C which was due to the increase of current flow by structural change related to the gelatinization of starch. The increase of temperature was faster when the frequency was increased, such as from 500 Hz to 1000 Hz. When potato was heated by ohmic heating at 60- 90 V and 40-120 Hz, rapid and uniform heat generation was possible. Thus, commercial utilization of ohmic heating can be applied for various types of vegetable foodstuff with ohmic heating was observed.

Ohmic heating is a heating method based on the principle when an electrical current passes through food. Since this method is internal, electrical current damage occurred during heating treatment. The results of ohmic heated starch’s external structure, X-ray diffraction, DSC analysis and RVA were differed from those of conventional heating at the same temperature. Several starches changed more rigid by structure re-aggregation. This change in starch was caused by change of physical, chemical, rheological property. The rheology of ohmic heated potato and corn starch of different heated methods were compared with chemically modified starch. After gelatinization, sample starch suspension (2%, 3%) measured flow curves by rheometer. Cross-linked chemically modified starch’s shear stress was decreased with degree of substitution reversibly. Ohmic heated more dramatic, at 60℃. Potato starch’s shear stress was less than commercial high cross-linked modified starch. Flow curves of potato starches measured at 4℃, 10℃, 20℃. Showed that Ohmic heated potato starch’s shear stress ranging between 4℃ and 20℃ was narrower than modified starch. According to this study, ohmic heated potato starch can be used by decreasing viscosity agent like cross-linked modified starch.

Ohmic heating is one of advanced thermal processing techniques which utilize conversion of electrical energy into heat. In our study, a feasibility of ohmic heating was tested to cook instant rice cake to improve energy efficacy as an alternative heating methods of conventional electrical kettle. Ohmic heating was conducted using customized ohmic cell (7.5×4.5×9.5 cm) equipped with titanium electrodes. Instant rice cakes in soup were ohmically heated up to 100°C at different electric fields (9, 12, 15 & 18 V/cm) and temperature holding times (60, 80, 100 & 120 s). Thermocouple was placed into both soup and rice cake to evaluate the temperature profile and energy efficacy. Temperature, voltage and current across the sample were measured and recorded at every 3 s using data acquisition system (DAQ). Mathematical model was developed to calculate the internal energy generation rate (QR, W). Internal energy generation rate (QR, W) was integrated versus temperature come-up time (s) to compute the total internal energy dose (ET, J) using MATLBA software. For energy efficacy (Eff), it was calculated ratio of total internal energy dose (ET, J) to heat quantity (Qh, J). During ohmic heating, temperature come-up time was significantly reduced as a function of elevated electric field (P<0.05). For example, 9V/cm of electric field showed 6.2±0.4 min of temperature come-up time up to 100°C. Higher electric field at 18 V/cm reduced temperature come-up time to 1.9±0.1 min. The electric field of 15 V/cm showed the best energy efficacy as 0.78 which meant 78% of electrical energy was converted into thermal energy for heating. In the texture profile analysis, the most preferable harness was found as 6.191 N at 15 V/cm and 100 s holding time. Our study showed the potential of ohmic heating to cook instant rice cakes for home meal replacement (HMR) and outdoor foods.

Ohmic heating is an internal heating method based on the principle that when an electrical current passes through food, electric resistance heat is uniformly generated internally by food resistance. Previous studies indicate that the thermal properties, external structure, internal structure, and swelling power of ohmic heat treated starch of various starches, such as potato, wheat, corn, and sweet potato, differed from those of conventional heating at the same temperature. In this study, the pasting property of starch, treated with ohmic and conventional heating, were measured by RVA (Rapid Visco-Analyzer). Our results show that as the ohmic heating temperature increased, the PV (Paste Viscosity) of the starch decreased significantly, and the PT (Pasting Temperature) increased. Changes in PV and PT indicate that the swelling of starch remains unchanged by ohm heating. The HPV (Hot Paste Viscosity), CPV (Cold Paste Viscosity) and SV (Setback Viscosity) of ohmic heated starch also differed from the conventional heated starch. The pasting property is similar to the viscosity curve of common cross-linked modified starch. In this experiment, we further confirm the similarity with modified starch and its usability.

Ohmic heating uses electric resistance heat which occurs equally and rapidly inside food when the electrical current is transmitted into. Prior to the study, we have researched the potato starch’s thermal property changes during ohmic heating. Comparing with conventional heating, the gelatinization temperature and the range of potato starch treated by ohmic heating are increased and narrowed respectively. This result is appeared equally at wheat, corn and sweet potato starch. At this study, we treated potato, wheat, corn and sweet potato starch by ohmic/conventional method and observed change of external structure by microscope and internal structure by X-ray diffractometer. Conventional heated at 55℃ potato starch was not external structural changes. But ohmic heated potato starch is showed largely change. Some small size starch particle were broken or small particles are made of larger particle together or small particles caught up in the large particle. Changes in ohmic heated potato starch at 60℃ was greater. The inner matter came to an external particle burst inside and only the husk has been observed. The same change was observed in the rest of the starch. The change of internal structure of potato starch was measured using X-ray diffraction patterns. There was no significant difference between ohmic and conventional heating at 55℃. But almost every peak has disappeared ohmic at 60℃. Especially 5.4° peak to represent the type B was completely gone. When viewed from the above results, external changes with change in the internal crystal structure of the starch particles were largely unknown to appear. In conclusion, during ohmic heating changes of starch due to the electric field with a change in temperature by the heating was found to have progressed at the same time.

Ohmic heating uses electric resistance heat which occurs equally and rapidly inside food when the electrical current is transmitted into. Prior to the study, we have researched the potato starch’s thermal property changes during ohmic heating. Comparing with conventional heating, the gelatinization temperature and the range of potato starch treated by ohmic heating are increased and narrowed respectively. Herein, we have studied thermal property changes of wheat, corn, potato and sweet potato starch by ohmic heating as well as conventional heating. And then we measure the water holding capacity of starches. Annealing of starch is a heat treatment method heated at 3~4% below the gelatinization point. This treatment changes the starch’s thermal property. In the DSC analysis of this study, the To, Tp, Tc of all starch levels have increased, and the Tc－To narrowed. In the ohmic heating, the treatment sample is extensively changed but not with the conventional heating. From the ohmic treatment, increases from gelatinization temperature are potato (8.3℃) > wheat (5.3℃) > corn (4.9℃) > sweet potato (4.5℃), and gelatinization ranges are potato (7.9℃), wheat (7.5℃), corn (6.1℃) and sweet potato (6.8℃). In the case of conventional treatment, water holding capacity is not changed with increasing temperature but the ohmic heating is increased. Water holding capacity is related to the degree of gelatinization for starch. This result show that when treated with below gelatinization temperature, the starches are partly gelatined by ohmic treatment. When viewing the results of the above, ohmic treatment is enhanced by heating and generating electric currents to the starch structure.

Ohmic heating uses electric resistance heat which occurs equally and rapidly inside of food when electrical current is flown into. In other study, we researched about soybean protein’s characteristic changes by ohmic heating. Nevertheless treated same temperature, denaturation of soybean protein were accelerated by ohmic heating than conventional heating. In this time, we studied thermal property change of potato starch by ohmic heating besides conventional heating. For this purpose, potato starch was heated at same subgelatinization temperature by ohmic and conventional heating. And thermal properties were tested using DSC. Annealing of starch is heat treatment method that heated at 3～4% below the gelatinization point. DSC analysis results of this study, the T_o, T_p, T_c of potato starch levels were increased, whereas T_c～T_o was narrowed. This thermal property changes appear similar to annealing’s result. It is thought the results shown in this study, because the heating from below the gelatinization point. 6, 12, 24, 72, and 120 hours heating at 55℃ for potato starch, T_o, T_p, T_c values continue to increased with heating time increase. The gelatinization temperature of raw potato starch was 65.9℃ and the treated starch by conventional heating at 55℃ for 120 hr was 72℃, ohmic was 76℃. The gelatinization range of conventional (72 hr) was 10℃, ohmic was 8℃. In case of 24 hours heating at 45, 50, 55, 60, 65℃ for potato starch, the result was similar to before. T_o, T_p, T_c values continue to increased and gelatinization range narrowed with heating temperature increase. In case of conventional heating at 60℃, the results of gelatinization temperature and range were 70.1℃ and 9.1℃. And ohmic were 74.4℃ and 7.5℃. When viewed through the results of the above, the internal structure of starch heated by ohmic heating was found that the shift to a more stable form and to increase the homology of the starch internal structure.

The low salt seasoned jeotkal, salted and fermented fisheries product, may has some problems, such as short shelf-life, its putrefaction by mining some microorganism from additives. It was considered that most microorganism in seasoned jeotkal were introduced from red pepper powder. Therefore, it is important to pasteurize red pepper powder for improving its microbial quality. When red pepper powder was pasteurized by ohmic heating, the survival cell concentration in red pepper powder was reduced to 1-log-unit at 500 V/m, 700 V/m, above 80℃. But viable cell counts were reduced from 8.5 × l0^6CFU/g to 2.1 × 10₂CFU/g, i.e. 4.6-log-unit, during ohmic heating at 90 for 40 min. Color values of red pepper powder during ohmic heating with different holding time were not changed significantly. When squid jeotkal was manufactured by using the pasteurized red pepper powder, viable cell counts of the product were decreased by about three log cycles, compare with control product. And also the counts of fungi were significantly decreased.