Effects of drying methods on drying characteristics, physicochemical properties and antioxidant capacity of okra

Results of an experimental study were presented and discussed for hot air drying with horizontal cut (HC-HA) or vertical cut (VC-HA) at 55, 60, 65, 70, 75, and 80 °C, respectively, and heat pump drying with HC (HC-HP) or VC (VC-HP) at 40, 50, 60, and 70 °C, respectively, on drying characteristic, colour quality, chemical compositions (vitamin C, chlorophyll, total phenolic and polysaccharide) and antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical scavenging capacity and oxygen radical absorbance capacity (ORAC)) of okra samples. Results showed VC had shorter drying time than that of HC both during HA and HP. The effective moisture diffusivity determined by Weibull distribution function ranged from 0.992 × 10−9 m2/s to 4.409 × 10−9 m2/s for HA, and 1.915 × 10−9 m2/s to 5.291 × 10−9 m2/s for HP. The drying activation was 37.00, and 35.91 kJ/mol for the samples of HC-HA and VC-HA, 29.25, and 21.40 kJ/mol for HC-HP and VC-HP, respectively. A comprehensive evaluation of quality attributes indicated that HP was more suitable for okra drying as it improved drying rate and drying quality compared with HA. The optimal sample quality (higher contents of chemical compositions and better colour quality) was found in okra treated with VC-HP at 50 °C.