Özet:

This study aimed to investigate the effect of different pretreatment blanching methods on the drying characteristics of green almonds. Microwave blanching at 300, 450, and 600 W power in the water and/or starch solution (0.5% w/w), water blanching (95℃, 5 min), and starch blanching (0.5% w/w) were preferred. Non-blanched samples were considered as the control samples. All samples were dried at a constant air velocity of 1.5 m/s and temperatures of 70, 90, and 110°C. As drying time increased, moisture ratio of all samples exponentially decreased. Nonlinear regression analysis was used to fit the experimental data to drying models. Effective diffusivities, which ranged from 2.238×10−9 to 6.434×10−9 m2 /s were calculated using Fick's second law of diffusion. Activation energies were determined according to the Arrhenius equation and ranged from 12.32 to 15.39 kJ/kg mol. The highest diffusion coefficient was observed in the microwave starch blanched (600 W-110°C) samples. The highest increases in the diffusion coefficient and decreases in the drying time in comparison with control samples were observed in the microwave-starch (600W- 70°C) samples. Thermal conductivity, density, and specific heat of samples ranged from 0.544-0.586 (W/m K), 3643.85-3900.00 (J/kg K), and 835.80-899.44 (Kg/m3), respectively. The friction drag force, convective heat, and mass transfer coefficients varied from 3.965 to 3.972×10−6 N, 66.29 to 66.44 W/m2 K, and 0.03410 to 0.03428 m/s, respectively. The using microwave-starch blanching pretreatment can significantly decrease the drying time and improve the drying process of green almond at the industrial scale.

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