Effect of Hot Water, Steam and Microwave Blanching on Colocasia esculenta Leaves

Abstract

Blanching, a pre-processing procedure, is usually carried out to inhibit enzymatic and other reactions which contribute to loss of quality prior to processing of green leafy vegetables. In this work the effect of hot water, steam and microwave blanching on peroxidase inactivation, colour changes, ascorbate degradation and changes in phenolic content of C. esculenta leaves was studied. Hot water and steam blanching were carried out in boiling water and steam, respectively, for 10, 20, 30, 60 and 120 s while microwave blanching was carried out for 5, 10, 15, 20 and 30 s. Peroxidase inactivation was faster in microwave blanched leaves. A 90% inactivation of peroxidase was achieved within 15 s of microwave blanching compared to 120 s and 30 s of hot water and steam blanching, respectively. The highest change in colour (ΔE) and chroma was observed after 20 s of microwave and steam blanching, respectively, although the changes were not significant. All the different blanching techniques resulted in ascorbate degradation, although higher losses were observed with hot water blanching compared to steam and microwave blanching.