Abstract: In order to explore the drying characteristics and quality of sweet purple potato using a far-infrared dryer, the effects of radiation temperature and distance on drying characteristics and nutrients including total phenols, total flavonoids, total sugar and VC were investigated. The results showed that drying time decreased and average drying rate increased significantly with an increase in radiation temperature and a reduction in radiation distance. The whole process of drying took place in the rate-falling period, thereby being mainly controlled by internal diffusion. The effective moisture diffusivity coefficient ranged from 2.42 × 10-10 to 4.64 × 10-10 m2/s and increased with an increase in radiation temperature and a reduction in radiation distance. The retention of total phenolics, total flavonoids, total sugar and VC was influenced significantly by radiation temperature and distance. The nutrient contents were very differently affected by temperature at different radiation distances. The optimal processing parameters were determined as radiation temperature of 240 ℃ and radiation distance of 14 cm based on comprehensive weighted scores. Under these optimized conditions, the drying time, and the contents of total phenols, total flavonoids, VC and total sugar were 270 min, 359.62, 223.13, 11.81 mg/100 g and 30.71 g/100 g, respectively. The drying rate and quality of dried product were both improved effectively by using far-infrared radiation. This study can provide a basis for the application of far-infrared radiation in the drying of sweet purple potato and other agricultural products.

Key words: sweet purple potato, far-infrared radiation, drying, quality characteristics