Drying characteristic and product color evaluation of yam by catalytic infrared drying

The aim of this study was to shorten the drying time and reduce the color deterioration during drying process. The drying curves and product color were investigated under different hot water blanching pre-treatment time ( 0.5, 1.0, 2.0, 3.0min) , slice thickness ( 0.5, 0.8, 1.0, 1.5 mm) and infrared radiation distance ( 30, 36, 42, 48 cm) by catalytic infrared drying.The results demonstrated that slice thickness and infrared radiation distance showed a significant impact on drying time ( p < 0.05) , and the drying rate would be improved by reducing the slice thickness and shortening the radiation distance. The drying time under slice thickness of 0.5 cm was reduced by about 47.73% compared with the slice thickness of 1.5 cm, and drying time under radiation distance of 30 cm was reduced by about 46.67% compared with the radiation distance of 48 cm. Blanching pre-treatment time ( 1.0, 2.0, 3.0 min) had no significant effect on drying time ( p > 0.05) .Yam slices samples showed only a falling rate period and the moisture effective diffusivity was between 1.4770 × 10-9m2/s and 5.5043 × 10-9m2/s by the Fick's second law.The whiteness index ( WI) value of dried yam products were between 56.19 and 78.78 under different pre-treatment and drying conditions.Through the analysis of drying time and products' color, the optimum processing condition was blanching time for 1~2 min, slice thickness of 1.0 cm, infrared radiation distance of 30 cm, the drying time was about 160 min and WI value was about 77.36.The results will provide a theoretic reference and technical supports for am slices drying process.