Quality changes in dehydrated dasheen leaves: effects of blanching pre-treatments and drying conditions

Abstract

The quality of dasheen leaves (Colocasia esculenta Linn Schott var. esculenta) dried at temperatures ranging from 40 to 70 ° C and under both natural and forced convection conditions was studied, in an attempt to develop a dehydrated product from this popular vegetable, often used in soups and commonly called ‘callaloo’. The effects of various pre-treatments on the quality of dasheen leaves dried at 60 °C and under natural and forced convection were also studied, viz.: steam blanching, water blanching and blanching in 0.06% magnesium carbonate at near boiling prior to immersion in a mixed chemical bath consisting mainly of sucrose. Drying of the fresh leaves to a moisture content of 2.0–6.2% db and at the highest temperatures of 60 and 70 °C resulted in undesirable colour changes from green, typical of the fresh vegetable to unattractive olive-brown or brown discolourations. Chlorophyll loss for leaves dried under natural convection was substantial compared with drying under forced convection, where drying times were substantially reduced. Ascorbic acid losses were severe irrespective of convection mode. Blanching of dasheen leaves in water or in an alkali bath followed by sucrose infusion and prior to drying at 60 °C resulted in superior products which, unlike the steam-blanched or unblanched leaves, showed minimal loss of green colour as reflected by chlorophyll and pheophytin contents as well as hue angle measurements.