No abstract

In this study, the effects of ohmic pre-drying technique on moisture ratio, drying rate, drying time, specific energy consumption, drying efficiency, and effective moisture diffusivity of tomato paste were investigated. Pre-drying experiments were carried out in an ohmic laboratory dryer at voltage gradient levels of 6, 8, 10, 12, 14, and 16 V/cm and oven at 105  and 1.0 m/s air velocity (control sample). Pre-drying was accomplished till the moisture content of the tomato paste reduced from initial moisture content of 90% (w.b.) to a safer level of 70% (w.b.). The ohmic pre-drying reduced the drying time of tomato paste by 80-97%, compared with the hot air drying. Pre-drying took place mainly in warming up, constant rate, and falling rate periods. Six available moisture-ratio models were fitted to the pre-drying data. The results showed that the Midilli et al. model is the most appropriate model for pre-drying behavior of tomato paste. The effective moisture diffusivity varied from 5.39 × 10(-8) to 3.91 × 10(-7)m(2)/s with an activation energy of 2.082 (V/g.cm). Both specific energy consumption and drying efficiency were considerably enhanced by increasing voltage gradient. It was found that the specific energy consumption and drying efficiency varied from 3.72 to 2.29 MJ/kg water and 67.8 to 83.8%, respectively.

Development of new technologies for thermal food treatment is still of great industrial and scientific interest. Ohmic heating is one of these new technologies. In this study, lemon juice was heated on a laboratory scale static ohmic at different voltage gradients in the range of 30–55V/cm. The voltage gradient was statistically significant on the ohmic heating rates for lemon juice (P < 0.05). Measurements were made from 20 to 74ºC and showed a linear increase in electrical conductivity values with increasing temperature. The ohmic heating system performance coefficients were in the range of 0.54–0.92.

The ohmic heating rate of a food is highly influenced by its electrical conductivity (σ). In this study, tomato was ohmically heated by using five different voltage gradients (6-14 V/cm). Measurements were made from 26 to 96°C and showed a linear increase in σ values with increasing temperature. The voltage gradient was statistically significant on the heating time (P < 0.05). The ohmic heating system performance coefficients were in the range of 0.716-0.905. The pH varied from 4.20 to 4.51, over the voltage gradient range studied.

In this paper, a laboratory microwave oven was used to dry the shrimp, applying microwave power in the four levels of 200, 300, 400 and 500W. Results indicated that drying took place in the falling rate period. The drying rate increased with drying microwave power, but decreased with moisture content. The effective diffusivity varied from 1.54×10 -10 to 1.43×10 -9 m 2 /s. About 22.54% increase in drying efficiency and about 28.94% (0.937MJ/kg[H 2 O]) decrease in specific energy consumption could be obtainable by increasing the microwave power from 200 to 500W.