İbrahim Doymaz

Convective air drying characteristics of thin layer carrots

Abstract The effects of air temperature, air-flow rate and sample thickness on drying kinetics of carrot cubes were investigated. Convective air drying characteristics of carrot cubes were evaluated in a cabinet dryer. Drying was carried out at 50, 60, 65, 70 °C and drying data were analyzed to obtain diffusivity values from the period of falling drying rate. In the falling rate period, moisture transfer from carrot cubes was described by applying the Fick’s diffusion model, and effective moisture diffusion coefficients were calculated. Effective diffusivity increased with increasing temperature. An Arrhenius relation with an activation energy value of 28.36 kJ/mol expressed effect of temperature on the diffusivity. Two mathematical models available in the literature were fitted to the experimental data. The Page model is given better prediction than the Henderson and Pabis model and satisfactorily described drying characteristics of carrot cubes.

Hot-air drying characteristics of red pepper

This work presents a theoretical and experimental study of the drying kinetics of red peppers under different pretreatment and air drying conditions. Red peppers, Capsicum annuum, grown in the region of Kahramanmaras, Turkey, were pretreated with various solutions of alkaline emulsion of ethyl oleate (AEEO) and dried afterwards. To date, there has been no work that studied the effect of AEEO pretreatment solution on the drying of red peppers. Our results indicated that pretreated peppers dried faster and had higher Hunter L (lightness), +a (redness) and +b (yellowness) values than the untreated and dried peppers. 2% ethyl oleate and 5% K2CO3 solution was found to be the most effective dipping solution that provided for whole peppers dried at 50 °C, and yielded best color quality. Drying curves of sliced peppers were obtained using the Page and exponential equations. Comparing the r2 values of both equations, it was concluded that the Page equation represents drying characteristics better than the exponential equation.

The effects of dipping pretreatments on air-drying rates of the seedless grapes

Turkey has a significant potential for fruit and vegetable production. Grape is an economically important item for Turkeys export. However, problems encountered during drying of grapes have not yet been resolved. The effects of different dipping solutions on hot air drying of grapes were studied. Seedless grapes pretreated with alkaline emulsion of ethyl oleate (AEEO) resulted in comparatively good quality raisins. Grapes dipped into ethyl oleate solution prior to drying showed shorter drying times than those untreated, or pretreated with potassium carbonate solution. Colour analysis of grapes showed that the best results are obtained in grapes which were pretreated with an AEEO and dried with air at 60 °C. The drying rates of grapes were modeled by the Page and Exponential equations. The model results agreed with experimental results.

An Experimental Study on Drying of Green Apples

Drying behavior of green apples in a laboratory dryer was examined. Prior to drying, the apples were cut in 8 mm thick slices, which were then treated with citric acid solution and blanched hot water at 80°C. Next, they were dried at 65°C with an air velocity of 2.0 m/s. The shortest drying time (270 min) was obtained with apples pretreated with citric acid solution. The drying data were fitted with 11 mathematical models available in the literature. Selection of the best model was investigated by comparing the determination of coefficient (R 2), reduced chi-square (χ2), root means square error ( RMSE ), and mean relative percentage error (P) between the experimental and predicted values. The results showed that the Wang and Singh, logarithmic, and Verma et al. models gave the best results in describing thin-layer drying of apple slices. The effective moisture diffusivity of pretreated samples with citric acid solution was higher than the other samples.

Drying of green bean and okra under solar energy

In this study, sun drying behaviours of green bean and okra were investigated. Drying experiments were conducted in Iskenderun-Hatay, Turkey. The drying study showed that the times taken for drying of green bean and okra from the initial moisture contents of 89.5% and 88.7% (w.b.) to final moisture content of around 15±0.5% (w.b.) were 60 and 100 h in open sun drying, respectively. The constant rate period is absent in drying curves. The drying process took place in the falling rate period. The drying data were fitted to thirteen thin-layer drying models. The performance of these models was investigated by comparing the determination of coefficient (R2), reduced chi-square (c2) and root mean square error (RMSE) between the observed and predicted moisture ratios. Estimations by Approximation of diffusion (for green bean) and Midilli et al. models (for okra) were in good agreement with the experimental data obtained.

Drying and Rehydration Behaviors of Convection Drying of Green Peas

The drying behaviors of green peas were examined in a convection dryer for a temperature range of 55–70°C with a constant air velocity of 2.1 m/s. The green peas were pretreated with ethyl oleate and citric acid solutions and blanched with hot water at 85°C before drying. The drying process was continued until sample moisture fell to 0.3 kg water/kg dry matter (dm). The blanched samples dried faster than those in other pretreatments and control conditions. Moreover, rehydration capacities of the pretreatments were higher than control samples. The experimental results illustrated the absence of a constant rate drying period and the drying process took place in the falling rate period. Moisture transfer from green peas was described by applying Ficks diffusion model, and the effective moisture diffusivity was calculated. The calculated effective diffusivity ranged from 8.059 × 10−11 to 1.973 × 10−10 m2/s for the studied temperature range. The values of activation energy (Ea) were 22.01, 26.86, 30.31, and 30.99 kJ/mol for samples pretreated with citric acid, control samples, samples pretreated with ethyl oleate, and blanched samples, respectively. Drying data were fitted to four thin-layer drying models; namely, Lewis, Henderson and Pabis, logarithmic, and Page. The performance of the models was evaluated by comparing the coefficient of determination (R2), reduced chi-square (χ2), and root mean square error (RMSE). The models that best represented green pea drying were the logarithmic and Page models.

Evaluation of Mathematical Models for Prediction of Thin-Layer Drying of Banana Slices

Drying characteristics of bananas were experimentally determined. The drying experiments were carried out in a hot air dryer at four inlet temperatures of 50, 60, 70 and 80°C, at a constant air velocity of 2.4 m/s and relative humidity of 4–25%. The experimental results were fitted to five thin-layer drying models and it was found that the Page and Logarithmic models gave better fit that the other models. Values of the effective diffusivity ranged from 7.374 × 10−11 to 2.148 × 10−10 m2/s. Activation energy for moisture diffusion of the banana slices was found to be 32.65 kJ/mol.

Characteristics of Thin-layer Infrared Drying of Green Bean

Doymaz I., Kipcak A.S., Piskin S. (2015): Characteristics of thin-layer infrared drying of green bean. Czech J. Food Sci., 33: 83–90. The effect of infrared (IR) power on drying kinetics, rehydration, and colour of green beans was investigated. The drying experiments were carried out at 83, 104, 125, 146, 167, and 188 W. It is observed that drying characteristics, rehydration, and colour of bean slices were greatly influenced by infrared power. The drying data were fitted with five thin-layer drying models available in the literature. Results showed that Midilli et al. and Aghbashlo et al. models are superior to the other models for explaining the drying kinetics of green bean slices. Effective moisture diffusivity was calculated in the range of 6.57 × 10–10 to 4.49 × 10–9 m2/s. Activation energy was estimated by a modified Arrhenius type equation and found to be 11.379 kW/kg.

Drying of pomegranate seeds using infrared radiation

Effect of different infrared (IR) power levels on drying kinetics of pomegranate seeds was investigated. The pomegranate seeds were dried at 83, 104, 125, and 146 W IR power levels. It was observed that the power levels affected the drying rate and time. Drying time reduced from 150 to 60 min as the IR power level increased from 83 to 146 W. The experimental data obtained from drying study were fitted with 10 mathematical models to evaluate the drying kinetics of the pomegranate seeds. The Page, Midilli et al., and Weibull models are given better prediction than the other models and satisfactorily described drying kinetics of pomegranate seeds. Effective diffusivity varied from 1.96 to 6.29×10−11 m2/s and was significantly influenced by IR power.

Hot-Air Drying and Rehydration Characteristics of Red Kidney Bean Seeds

The effects of pretreatments such as citric acid and hot water blanching and air temperature on drying and rehydration characteristics of red kidney bean seeds were investigated. Drying experiments were carried out at four different drying air temperatures of 50°C, 60°C, 70°C, and 80°C. It was observed that drying and rehydration characteristics of bean seeds were greatly influenced by air temperatures and pretreatments. Four commonly used mathematical models were evaluated to predict the drying kinetics of bean seeds. The Weibull model described the drying behaviour of bean seeds at all temperatures better than the other models. The effective moisture diffusivities (Deff) of bean seeds were determined using Ficks law of diffusion. The values of Deff were between 1.25 × 10−9 and 3.58 × 10−9 m2/s. Activation energy was estimated by an Arrhenius-type equation and was determined as 24.62, 21.06, and 20.36 kJ/mol for citric acid, blanch, and control samples, respectively.