Abstract: In order to improve the hot-air drying efficiency and the product quality, the drying characteristics and quality changes of red-fleshed pitaya were evaluated at different slice thicknesses (6, 8, 10 and 12 mm) and drying temperatures (50, 60, 70 and 80 ℃). The results showed that higher temperature and thinner slices led to higher drying rate and shorter drying time. The Page model could well reflect the change of moisture ratio with thickness and drying temperature during hot air drying. The effective moisture diffusion coefficient of red-fleshed pitaya ranged from 3.537 4 × 10-10–19.942 6 × 10-10 m2/s. The hot-air drying activation energy for 6, 8, 10, and 12 mm thick pitaya slices were 32.985 7, 27.086 1, 26.889 4 and 17.792 9 kJ/mol, respectively. Higher total phenol content and antioxidant activity were observed for the dried product obtained at drying temperature of 70 ℃, slice thickness of 6 mm and drying time of 6 h. Drying temperature and slice thickness had no significant effect on the color of the product.

Key words: red-fleshed pitaya, hot air drying, kinetic model, effective moisture diffusion coefficient, activation energy