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Microwave assisted fluidized bed drying is a novel drying technique which reduces drying time and yields higher quality products. In this study the effect of this method on color changes of whole and cut hazelnut kernels was investigated. The parameters of color and resulting total color change, chroma, Hue angle and browning index were also calculated during drying in three temperatures (40, 50 and 60°C) and microwave power levels (0, 450 and 900W). Comparison was made to investigate the effect of drying condition on browning of hazelnut surface and internal cavity. The zero and first order kinetic models were also fitted to whole and cut kernel color parameters. The results showed similar behavior in color parameters of whole and cut kernels. L value and Hue angle decreased with increasing drying time, drying air temperature and microwave power but a, b, ΔE, chroma and browning index increased. L and b values of whole kernels were higher than cut kernels but the a value was lower. Zero-order model was selected as the best model for predicting a, b and ΔE while first order model best described the kinetics of color changes of L, chroma, Hue angle and browning index. [ABSTRACT FROM AUTHOR]

The main target of this research is drying raspberries in a Microwave assisted fluidized bed dryer. In order to evaluate and predict the quality properties of this fruit, Response Surface Methodology (RSM) was used. In this research, the effects of five variables: power of microwave (0, 300 and 600 W), temperature (55, 70 and 85 C), air flow rate (15, 20 and 25 m/s), starting time of microwave input (from the moment when the moisture content decreased until 334, 400 and 466 g water per 100 g dry matter) and amount of material (50, 100 and 150 g) on the rehydration capacity and loss of anthocyanins content were studied. Experiments were designed according to Central Composite Rotatable Design with these five factors each at three different levels, including central and axial points. With respect to the dependent variables, both linear and quadratic effects of all of the five independent variables on Rehydration Capacity and loss of anthocyanins content were found to be significant. For each response, second order polynomial models were developed using multiple linear regression analysis. Analysis of variance (ANOVA) was performed to check the adequacy and accuracy of the fitted models. According to our results, the optimal point for both characteristics were as follows: microwave power 600 W, temperature 74 , the air flow rate 3/22 meters per second and 53 grams of the substance, starting from the moment the microwave 466 percent moisture content was reduced. Model to predict the dependent variables with empirical results obtained were very close. [ABSTRACT FROM AUTHOR]

In the present study, a pilot scale microwave assisted fluidized-bed dryer was designed and used to dry apple cubes. A model was developed to describe heat and mass transfer in apple cubes during drying in a combined microwave-assisted fluidized-bed dryer. A numerical solution based on the finite difference method was used to develop the model for moisture distribution and temperature variation of samples. The model was validated using experimental data, including average moisture content, center and surface temperature at various air temperatures and microwave power densities. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the changes of optical properties of apple (Golden Delicious) slices during drying. The optical parameters compared on the basis of Hunter values (L, a, b) changes as well as total color difference (ΔE) and browning index (BI). The effect of coating materials including carboxymethylcellulose (CMC), starch, and pectin as well as microwave treatment on optical properties and microstructure of dried samples were investigated. To analyze the effects of these processes on microstructure, scanning electron microscopy (SEM) was employed. Results showed that optical properties as well as microstructure of apple were affected by coating material and drying condition. Coated samples by CMC had a lower L and higher BI, but different results in the presence of starch were obtained. Microwave treatment in the presence of appropriate coating materials could improve the optical properties of dried apple slices. [ABSTRACT FROM AUTHOR]

The effect of coating, hot-air and microwave drying on the texture, microstructure and rehydration characteristics of Golden Delicious apple slices (22 mm diameter, 4 mm thickness) was investigated. Blanching was carried out in hot water (80°C, 1 min) to prevent undesirable enzymatic reactions. To induce a porous structure during microwave treatment, coating with a starch (suspension), pectin and carboxymethylcellulose (CMC) solution (20 g/L) with and without CaCI2 (10 g/L) was carried out. A puncture test and a scanning electron microscopy (SEM) technique were used to analyse the effects of these processes on texture and microstructure. Rehydration in distilled water was also studied. Coating, air-drying (70°C, 1.5 m/s) and microwave treatment (300 W, 10s) resulted in the production of puffed and porous products. Microstructure of samples mated by starch and pectin with CaCI2 improved. Coating had a beneficial effect on the microstructure of samples after microwave treatment. In addition, microstructural studies showed that mating with pectin had a significant effect on the thickness of the cell wall whereas those treated with starch or CMC did not exhibit such an effect. Adding CaCI2 to the coating solution improved the microstructural properties and prevented central heating phenomena. [ABSTRACT FROM AUTHOR]