Characterization of single and hybrid mode drying of desiccated coconut

Abstract

Desiccated coconut was dried using a novel hybrid dryer that was developed to work in both single and hybrid mode. Single mode consisted of convective (CD) and infrared (IR) drying while hybrid mode involved combined (IRCD) and sequential (IR-IRCD) drying. The effect of two different drying modes, four drying methods with constant temperature process (50, 60, 70 °C) on the drying time, specific energy consumption (SEC), effective moisture diffusivity, color change (ΔE), whiteness index (WI), oil content, free fatty acid (FFA), peroxide value (PV) and microstructure of desiccated coconut were investigated and analysed. The results showed that the drying time was reduced by the increase in drying temperature, where sequential IR-IRCD had the shortest drying time followed by IR, IRCD and CD. In contrast, effective moisture diffusivity was increased by the increase in drying temperature. IR drying had the lowest SEC followed IR-IRCD, IRCD and CD. Hybrid mode IR-IRCD proved to be the best in retaining the color of desiccated coconut with the lowest ΔE and highest WI. Desiccated coconut from all drying methods had acceptable value of oil content, free fatty acid and peroxide value. IR-IRCD at 70 °C was chosen to be the most suitable for drying desiccated coconut based on the combined effect of drying time (28 min), SEC (28.15 kWh/kg), effective moisture diffusivity (3.780 × 10−9 ± 0.19 × 10−9 m2/s), ΔE (1.67 ± 0.04), WI (73.89 ± 0.26), oil content (61.33 ± 0.15 g/100 g), FFA (0.076 ± 0.003 g/100 g) and PV (1.66 ± 0.15 mEq/kg).