Drying characteristics of Chinese Yam ( Dioscorea opposita Thunb .) by far-infrared radiation and heat pump

Chinese Yam chips were dried using a heat pump (HP) dryer alone or in combination with far infrared radiation (FIR) at 500, 1000 and 2000 W (500 FIR, 1000 FIR, and 2000 FIR, respectively). The experimental results were presented in terms of the drying characteristics, and dried product qualities (shrinkage, color, texture, percentage of rehydration, and moisture content). Samples with initial moisture content of approximately 76% (w.b.) were dried to a final moisture content of <17% (w.b.) at the drying temperature of 50 °C and at an air flow rate of 1.0 m s−1 for all of the experiments. The data showed that FIR + HP drying increased the drying rate by reducing the drying time, and the resulted dried Chinese Yam chips generally had higher values of lightness and comparable values of redness and yellowness than the HP-treated samples. In the case of HP + 1000FIR, the dried Chinese Yam chips had lower shrinkage, improved rehydration ability, lower hardness and higher brittleness than those dried by HP, HP + 500FIR and HP + 2000FIR. It is worth noting that the total energy used for FIR-assisted drying processes decreased with the increase of FIR intensity. The present data suggest that HP + FIR drying is an effective and economical method for Chinese Yam chip drying, and HP + 1000FIR can obtain the best dried product.