Abstract An ohmic assisted vacuum evaporation (OAVE) processes was used to concentrate orange jui... more Abstract An ohmic assisted vacuum evaporation (OAVE) processes was used to concentrate orange juice from 11.4% total soluble solid content (TSSC) to 42% TSSC by applying 13 V/cm constant voltage gradient at different temperatures. The evaporation temperatures were adjusted to 100 °C, 85 °C, 75 °C and 65 °C by setting absolute system pressures of 101.32 kPa, 58 kPa, 39 kPa and 25 kPa, respectively. The total time for the processes, including heating and evaporation, was 34, 40, 48, and 54 minutes for 100, 85, 75, and 65 °C, respectively. As the evaporation temperature increased, the applied energy required for phase change decreased while maximum current values increased from 0.6 A at 65 °C to 2.52 A at 100 °C. During any given run, the current value increased as the orange juice pulp heated up, but then decreased after it began to boil, leading to a reduction in the rate of heat generation. Increasing evaporation temperature has a positive effect on evaporation rates, energy efficiency, specific water removal ratio (SWRR), exergy efficiency, and Improvement Potential (IP) (p
Abstract The ohmic thawing (OT) of minced meat sample was mathematically modelled using different... more Abstract The ohmic thawing (OT) of minced meat sample was mathematically modelled using different numerical methods (Finite Difference-FD and Finite Volume-FV) for different process conditions (voltage gradients of 10, 13 and 16 V/cm and fat contents of meat sample as 2%, 10% and 18%). FD method was successful to predict the temperature changes for both heating and phase change regions. FV method was performed by using two different heat generation functions; depending on process time (UDF-1) or the center temperature (UDF-2). The description of the change of heat generation term depending on process time (UDF-1) in the ANSYS module was more successful with the experimental data compared to the description of the change of heat generation term depending the center temperature (UDF-2). Although FV model is more complex than FD model it can be applied for simulation of detailed temperature distributions. On the other hand, FD model can be applied for practical predictions of temperature histories for center temperatures in simple geometries. It is thought that the simulation of OT performed at different conditions with the FD and the FV methods would contribute valuable data in the design of household ohmic thawing/cooking systems for solid food materials.
Thin-layer drying behaviour of dill leaves samples under three different infrared radiation power... more Thin-layer drying behaviour of dill leaves samples under three different infrared radiation power intensities was investigated. Diffusion Approach was found to be the best model that describes the drying behaviour of dill leaves. Effective diffusivity values were 6.97 × 10−9, 6.84 × 10−9 and 8.96 × 10−9 m2/s for power intensities of 1790, 1970 and 2070 W/m2, respectively. According to the first and second law efficiencies, the infrared drying system was more efficient at higher power intensities (p
Sour cherry juice having total soluble solids (TSS) of 19.2% was evaporated up to 65% TSS at vacu... more Sour cherry juice having total soluble solids (TSS) of 19.2% was evaporated up to 65% TSS at vacuum (gauge pressure of 580 mm-Hg) by applying ohmic heating at three different voltage gradients (10–14 V/cm). Total process times were determined as 40, 55, 75, and 85 min for 14 V/cm, 12 V/cm, and 10 V/cm, and vacuum evaporation (VE), respectively. The change of moisture content during ohmic assisted vacuum evaporation and VE processes were investigated by seven different empirical models. The best fitting model was Midilli model for three different voltage gradients and VE. The electrical conductivity values at different voltage gradients varied between 0.41 and 1.13 S/m for different TSS contents. The changes of EC values were examined in detail for three different regions; heating up period, first evaporation period, and second evaporation period. EC increased until a critical % TSS content (32% TSS), then remained constant for certain time (until 45% TSS) depending on voltage gradient, and then it had tendency to decrease. Ohmic heat generation increased sharply during heating period, then decreased dramatically during evaporation periods. It is recommended that ohmic heating could be alternatively used as the heat source to shorten the process times of vacuum evaporation applied for concentration of fruit juices.
The effectiveness of combined ohmic–infrared cooking system on the microbiological quality of mea... more The effectiveness of combined ohmic–infrared cooking system on the microbiological quality of meatballs was studied. In the first step, samples were precooked in an ohmic heater at 15.26 V/cm. In the second step, ohmically precooked samples were processed in the infrared heater for the final cooking purpose at different combinations of heat fluxes (3.7, 5.7, 8.5 kW/m2), application distances (10.5, 13.5, 16.5 cm) and application times (4, 8, 12 min). The effects of infrared process conditions on total mesophilic aerobic bacteria (TMAB) counts of meatball samples were investigated. TMAB counts of meatball samples were reduced, ranging between 1.96 and 4.50 logarithmic units, depending on infrared process conditions used. Mold and yeast, Staphylococcus aureus, Clostridium perfringens, Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 were not detected in the treated meatball samples. The effects of different infrared cooking conditions both on cooking value and pasteurization value were also determined. These results demonstrate the considerable potential for the application of ohmic–infrared combination cooking process to the meatballs. Practical Applications Meat is a nutritious substrate for the growth of microorganisms and is highly susceptible to spoilage. The raw meat contaminated with pathogenic microorganisms is one of the main sources of foodborne illness. During conventional cooking, the interior region may not heat sufficiently and pathogens could survive in the product, unless the meat products have been properly heat-treated. Therefore, there is a potential need for alternative cooking technologies, which provide a valuable tool to reduce the risk of pathogen growth in the products while shortening the treatment time. In this study, the combination of ohmic and infrared heating technologies was used for cooking of the meatball.
Ohmic cooking of meatballs was conducted in a continuous type ohmic cooker using different voltag... more Ohmic cooking of meatballs was conducted in a continuous type ohmic cooker using different voltage gradients (15, 20 and 25 V/cm) and holding times (0, 15 and 30 s). The color and textural properties and log reductions in total microbial count of the meatballs were assessed. The effects of process variables on these responses were evaluated by linear and quadratic mathematical models. Desirability function was used to determine the optimum ohmic pre-cooking condition by considering the criteria of minimizing hardness ratio, and maximizing chewiness ratio, resilience ratio, log reduction in microbial load, outside chroma ratio, inside chroma ratio and in range of springiness, gumminess and inside L ratios. The optimum ohmic pre-cooking condition was found to be a 15.26 V/cm voltage gradient with no holding time. It is concluded that application of the optimum condition in the related ohmic system offers potential for the production of high quality and safe semi-cooked meat products.
Ohmic heating is an alternative fast heating method for food products. In this study, the pea pur... more Ohmic heating is an alternative fast heating method for food products. In this study, the pea puree samples were blanched ohmically and conventionally. The ohmic blanching was performed by application of four different voltage gradients in the range of 2050 V/cm. The puree ...
Turkish Journal of Agriculture - Food Science and Technology
The rheological properties of koumiss were investigated at different temperatures (4, 10, and 20°... more The rheological properties of koumiss were investigated at different temperatures (4, 10, and 20°C). Experimental shear stress–shear rate data were fitted to different rheological models. The consistency of koumiss was predicted by using the power-law model since it described the consistency of koumiss best with highest regression coefficient and lowest errors (root mean square error and chi-square). Koumiss exhibited shear thinning behavior (n
The analytical model developed by Dincer and Dost [3] for the estimation of diffusivities and mas... more The analytical model developed by Dincer and Dost [3] for the estimation of diffusivities and mass transfer coefficients has been reviewed, and the equations used for the evaluation of the mass transfer coefficients have been corrected. The corrected equations have been used for the calculation of mass transfer coefficients from literature data. It was observed that the corrected diffusivities showed significant differences from the previously calculated values. The use of the modified equations in future drying calculations will lead to more realistic mass transfer coefficient values.
The accuracy of the two simplified methods; Dincer and Dost (1996) and Dincer and Hussain (2004),... more The accuracy of the two simplified methods; Dincer and Dost (1996) and Dincer and Hussain (2004), used for the determination of the first root of the characteristic equation and the Biot numbers from experimental lag factor data in unidirectional drying of solids has been investigated. The tabulated values relating the lag factor to the first root of the characteristic equation and Biot number were taken as basis in the assessment. None of the methods considered yielded accurate predictions for the complete lag factor range. The calculation of μ1 and Biot number from the tabulated values of lag factors has been recommended.
An analytical equation for uniform, normal surface microwave power for cylindrical objects has be... more An analytical equation for uniform, normal surface microwave power for cylindrical objects has been proposed. The surface microwave power for cylindrical objects undergoing unidirectional energy transfer was a function of average power absorbed, dimensions of the cylinder and the attenuation constant. A finite difference model has been developed to predict the temperature profiles. The numerical model has been tested against well-known analytical solutions and excellent agreement was observed. This model has been used to simulate literature temperature profiles. Satisfactory agreements were obtained for the interior points. However, the predicted surface temperatures were higher than the experimental temperatures. It is believed that the proposed expression for the surface power may be used to check the uniformity and normalcy of the surface microwave
Publisher Summary Ohmic heating is an electroheating technique based on the passage of electrical... more Publisher Summary Ohmic heating is an electroheating technique based on the passage of electrical current through a food product having electrical resistance. The advantage of ohmic treatments over conventional methods is the lack of high wall temperatures and limiting heat transfer coefficients requirements. Its other advantages include maintaining the color and nutritional value of food, short processing time, and higher yield. This chapter focuses on the application of the novel thermal technology of ohmic heating. It discusses the liquid food conductivity as a controlling process parameter. Furthermore, it reviews the effects of this electric resistance heating on the microbial and chemical properties of different studied liquid food products and addresses the main industrial applications as well as future trends of this thermal treatment. Ohmic heating is applied to liquid foods such as fruit and vegetable products, milk, ice-cream mix, eggs, whey, soups, stews, fruits in syrup...
Abstract An ohmic assisted vacuum evaporation (OAVE) processes was used to concentrate orange jui... more Abstract An ohmic assisted vacuum evaporation (OAVE) processes was used to concentrate orange juice from 11.4% total soluble solid content (TSSC) to 42% TSSC by applying 13 V/cm constant voltage gradient at different temperatures. The evaporation temperatures were adjusted to 100 °C, 85 °C, 75 °C and 65 °C by setting absolute system pressures of 101.32 kPa, 58 kPa, 39 kPa and 25 kPa, respectively. The total time for the processes, including heating and evaporation, was 34, 40, 48, and 54 minutes for 100, 85, 75, and 65 °C, respectively. As the evaporation temperature increased, the applied energy required for phase change decreased while maximum current values increased from 0.6 A at 65 °C to 2.52 A at 100 °C. During any given run, the current value increased as the orange juice pulp heated up, but then decreased after it began to boil, leading to a reduction in the rate of heat generation. Increasing evaporation temperature has a positive effect on evaporation rates, energy efficiency, specific water removal ratio (SWRR), exergy efficiency, and Improvement Potential (IP) (p
Abstract The ohmic thawing (OT) of minced meat sample was mathematically modelled using different... more Abstract The ohmic thawing (OT) of minced meat sample was mathematically modelled using different numerical methods (Finite Difference-FD and Finite Volume-FV) for different process conditions (voltage gradients of 10, 13 and 16 V/cm and fat contents of meat sample as 2%, 10% and 18%). FD method was successful to predict the temperature changes for both heating and phase change regions. FV method was performed by using two different heat generation functions; depending on process time (UDF-1) or the center temperature (UDF-2). The description of the change of heat generation term depending on process time (UDF-1) in the ANSYS module was more successful with the experimental data compared to the description of the change of heat generation term depending the center temperature (UDF-2). Although FV model is more complex than FD model it can be applied for simulation of detailed temperature distributions. On the other hand, FD model can be applied for practical predictions of temperature histories for center temperatures in simple geometries. It is thought that the simulation of OT performed at different conditions with the FD and the FV methods would contribute valuable data in the design of household ohmic thawing/cooking systems for solid food materials.
Thin-layer drying behaviour of dill leaves samples under three different infrared radiation power... more Thin-layer drying behaviour of dill leaves samples under three different infrared radiation power intensities was investigated. Diffusion Approach was found to be the best model that describes the drying behaviour of dill leaves. Effective diffusivity values were 6.97 × 10−9, 6.84 × 10−9 and 8.96 × 10−9 m2/s for power intensities of 1790, 1970 and 2070 W/m2, respectively. According to the first and second law efficiencies, the infrared drying system was more efficient at higher power intensities (p
Sour cherry juice having total soluble solids (TSS) of 19.2% was evaporated up to 65% TSS at vacu... more Sour cherry juice having total soluble solids (TSS) of 19.2% was evaporated up to 65% TSS at vacuum (gauge pressure of 580 mm-Hg) by applying ohmic heating at three different voltage gradients (10–14 V/cm). Total process times were determined as 40, 55, 75, and 85 min for 14 V/cm, 12 V/cm, and 10 V/cm, and vacuum evaporation (VE), respectively. The change of moisture content during ohmic assisted vacuum evaporation and VE processes were investigated by seven different empirical models. The best fitting model was Midilli model for three different voltage gradients and VE. The electrical conductivity values at different voltage gradients varied between 0.41 and 1.13 S/m for different TSS contents. The changes of EC values were examined in detail for three different regions; heating up period, first evaporation period, and second evaporation period. EC increased until a critical % TSS content (32% TSS), then remained constant for certain time (until 45% TSS) depending on voltage gradient, and then it had tendency to decrease. Ohmic heat generation increased sharply during heating period, then decreased dramatically during evaporation periods. It is recommended that ohmic heating could be alternatively used as the heat source to shorten the process times of vacuum evaporation applied for concentration of fruit juices.
The effectiveness of combined ohmic–infrared cooking system on the microbiological quality of mea... more The effectiveness of combined ohmic–infrared cooking system on the microbiological quality of meatballs was studied. In the first step, samples were precooked in an ohmic heater at 15.26 V/cm. In the second step, ohmically precooked samples were processed in the infrared heater for the final cooking purpose at different combinations of heat fluxes (3.7, 5.7, 8.5 kW/m2), application distances (10.5, 13.5, 16.5 cm) and application times (4, 8, 12 min). The effects of infrared process conditions on total mesophilic aerobic bacteria (TMAB) counts of meatball samples were investigated. TMAB counts of meatball samples were reduced, ranging between 1.96 and 4.50 logarithmic units, depending on infrared process conditions used. Mold and yeast, Staphylococcus aureus, Clostridium perfringens, Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 were not detected in the treated meatball samples. The effects of different infrared cooking conditions both on cooking value and pasteurization value were also determined. These results demonstrate the considerable potential for the application of ohmic–infrared combination cooking process to the meatballs. Practical Applications Meat is a nutritious substrate for the growth of microorganisms and is highly susceptible to spoilage. The raw meat contaminated with pathogenic microorganisms is one of the main sources of foodborne illness. During conventional cooking, the interior region may not heat sufficiently and pathogens could survive in the product, unless the meat products have been properly heat-treated. Therefore, there is a potential need for alternative cooking technologies, which provide a valuable tool to reduce the risk of pathogen growth in the products while shortening the treatment time. In this study, the combination of ohmic and infrared heating technologies was used for cooking of the meatball.
Ohmic cooking of meatballs was conducted in a continuous type ohmic cooker using different voltag... more Ohmic cooking of meatballs was conducted in a continuous type ohmic cooker using different voltage gradients (15, 20 and 25 V/cm) and holding times (0, 15 and 30 s). The color and textural properties and log reductions in total microbial count of the meatballs were assessed. The effects of process variables on these responses were evaluated by linear and quadratic mathematical models. Desirability function was used to determine the optimum ohmic pre-cooking condition by considering the criteria of minimizing hardness ratio, and maximizing chewiness ratio, resilience ratio, log reduction in microbial load, outside chroma ratio, inside chroma ratio and in range of springiness, gumminess and inside L ratios. The optimum ohmic pre-cooking condition was found to be a 15.26 V/cm voltage gradient with no holding time. It is concluded that application of the optimum condition in the related ohmic system offers potential for the production of high quality and safe semi-cooked meat products.
Ohmic heating is an alternative fast heating method for food products. In this study, the pea pur... more Ohmic heating is an alternative fast heating method for food products. In this study, the pea puree samples were blanched ohmically and conventionally. The ohmic blanching was performed by application of four different voltage gradients in the range of 2050 V/cm. The puree ...
Turkish Journal of Agriculture - Food Science and Technology
The rheological properties of koumiss were investigated at different temperatures (4, 10, and 20°... more The rheological properties of koumiss were investigated at different temperatures (4, 10, and 20°C). Experimental shear stress–shear rate data were fitted to different rheological models. The consistency of koumiss was predicted by using the power-law model since it described the consistency of koumiss best with highest regression coefficient and lowest errors (root mean square error and chi-square). Koumiss exhibited shear thinning behavior (n
The analytical model developed by Dincer and Dost [3] for the estimation of diffusivities and mas... more The analytical model developed by Dincer and Dost [3] for the estimation of diffusivities and mass transfer coefficients has been reviewed, and the equations used for the evaluation of the mass transfer coefficients have been corrected. The corrected equations have been used for the calculation of mass transfer coefficients from literature data. It was observed that the corrected diffusivities showed significant differences from the previously calculated values. The use of the modified equations in future drying calculations will lead to more realistic mass transfer coefficient values.
The accuracy of the two simplified methods; Dincer and Dost (1996) and Dincer and Hussain (2004),... more The accuracy of the two simplified methods; Dincer and Dost (1996) and Dincer and Hussain (2004), used for the determination of the first root of the characteristic equation and the Biot numbers from experimental lag factor data in unidirectional drying of solids has been investigated. The tabulated values relating the lag factor to the first root of the characteristic equation and Biot number were taken as basis in the assessment. None of the methods considered yielded accurate predictions for the complete lag factor range. The calculation of μ1 and Biot number from the tabulated values of lag factors has been recommended.
An analytical equation for uniform, normal surface microwave power for cylindrical objects has be... more An analytical equation for uniform, normal surface microwave power for cylindrical objects has been proposed. The surface microwave power for cylindrical objects undergoing unidirectional energy transfer was a function of average power absorbed, dimensions of the cylinder and the attenuation constant. A finite difference model has been developed to predict the temperature profiles. The numerical model has been tested against well-known analytical solutions and excellent agreement was observed. This model has been used to simulate literature temperature profiles. Satisfactory agreements were obtained for the interior points. However, the predicted surface temperatures were higher than the experimental temperatures. It is believed that the proposed expression for the surface power may be used to check the uniformity and normalcy of the surface microwave
Publisher Summary Ohmic heating is an electroheating technique based on the passage of electrical... more Publisher Summary Ohmic heating is an electroheating technique based on the passage of electrical current through a food product having electrical resistance. The advantage of ohmic treatments over conventional methods is the lack of high wall temperatures and limiting heat transfer coefficients requirements. Its other advantages include maintaining the color and nutritional value of food, short processing time, and higher yield. This chapter focuses on the application of the novel thermal technology of ohmic heating. It discusses the liquid food conductivity as a controlling process parameter. Furthermore, it reviews the effects of this electric resistance heating on the microbial and chemical properties of different studied liquid food products and addresses the main industrial applications as well as future trends of this thermal treatment. Ohmic heating is applied to liquid foods such as fruit and vegetable products, milk, ice-cream mix, eggs, whey, soups, stews, fruits in syrup...
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