Drying of African leafy vegetables for their effective preservation: the difference in moisture sorption isotherms explained by their microstructure

Abstract

The problem of malnutrition and nutrition deficiency, as well as droughts that lead to reduction in food supply and starvation, is well documented for Sub-Saharan Africa. Reducing post-harvest losses of five species of African leafy vegetables (ALVs) by preservation through drying is studied herein. Energy efficient gentle drying conditions using superabsorbent polymers and a temperature of 40 °C were shown to preserve most leaf structures and vitamins. The microbial safe moisture content of the ALVs was found to be ≤14% dry basis. Dried Slender Leaf and Nightshade leaves could be rehydrated to the equilibrium moisture content of fresh leaves upon dry storage, while it was not possible for Jute Mallow, Cowpea and Amaranthus. This was attributed to different palisade parenchyma cell lengths. An increased amount of starch granules as observed in the microstructure of Cowpea and Nightshade leaves is suggested to explain their fibrous texture upon cooking. These results show that the ALVs can be effectively preserved using the same drying method and that this can be used to fight micro-nutrient deficiencies during droughts.