Application of microwaving for blanching taro and yam

Abstract

The leaching losses of potassium from taro and yam during soaking in hot water were examined at four temperatures ranging from 70° to 100°. In order to describe this phenomenon quantitatively, the leaching losses and measured data were fitted to the infinite cylinder diffusion model using a non-linear least squares method. Therefore, the measured results agreed well with the calculated results. The values of the estimated diffusion coefficients were 0.94×10-6 to 1.34×10-6 in taro and 1.41×10-6 to 1.60×10-6 (m2.s -1) in yam, and the apparent activation energies determined from an Arrhenius-type equation were 12.6 and 4.9 (kJ.mol-1), respectively. The applicability of microwaving for blanching taro and yam was also examined. Changes in enzyme (peroxidase) activity, color, hardness, weight and potassium content were compared for three blanching methods (microwave radiation of wrapped and unwrapped samples and immersion in boiling water). Microwave blanching of wrapped samples required the least time for enzyme inactivation. Color differences (^Delta;E) after blanching were 5.3-11.7 in taro and 15.9-19.0 in yam. Samples became significantly softer after microwave blanching, and wrapping reduced weight loss during microwave heating. While samples heated by immersion in hot water lost a large amount of potassium, microwave blanching did not result in loss of potassium. These results suggest that microwaving is useful for blanching taro and yam.