Dehydration of yam slices using FIR-assisted freeze drying

Yam dehydration was studied using freeze drying with far-infrared radiation. The study was performed using a three-level, three-factor design and aimed to determine the optimum combination of drying temperature (X-1), distance between sample and FIR heater (X-2), and thickness (X-3) that led to the best results of drying time, rehydration ratio, and total color difference. The response variables of drying time and rehydration ratio were significantly affected by drying temperature (X-1) and thickness (X-3) at the 5% significance level. On the other hand, total color difference was significantly affected by distance (X-2) at 95% level confidence. The coefficients of determination (R-2) of surface response models of drying time, rehydration ratio, and total color difference were all found to be over 0.95. The optimum drying processing could be established at 50 mm distance from FIR plate and by controlling the drying temperature in the range of 34-37 degrees C and slices thickness of 7-8 mm for freeze drying with FIR heating of products. Verification tests indicated that the generated second-order polynomial models were acceptable. Optimum drying conditions were recommended and validation proved the results to be adequate and acceptable. (c) 2006 Elsevier Ltd. All rights reserved.