The influence of storage conditions on the stability of b-carotene in solar-dehydrated dark green leafy vegetables
Ndiritu, James Wanjohi
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Adequate consumption of fruits and vegetables is effective in prevention and combating micronutrient deficiencies such as vitamin A deficiency (VAD). Pre-formed vitamin A sources of food such as meat, milk and eggs are not always available to the poor in developing countries and dark-green leafy vegetables (DGLV) are the main source of these vitamins in the diet of many people. In many rural communities in Kenya, these vegetables constitute the main diet in many households. They supply most of the vitamin A and minerals requirements such as calcium, zinc and iron. These vegetables grow in plenty during the rainy season but become scarce or not available during the dry season and in times of drought. Their consumption and availability is limited to the wet season due to the lack of proper preservation and storage procedures. In some areas, traditional methods of sun drying are used but these results in a significant loss of vitamin value in these vegetables. Subsequent losses are experienced when the dried vegetables are stored under ambient (normal) conditions. A major concern in the nutritional value of these vegetables is the loss of carotenoids during dehydration and in storage, b-Carotene, the major carotenoid in these vegetables is known to undergo an oxidative degradation during dehydration and storage of these vegetables. An ideal storage procedure for these vegetables should eliminate oxygen in the packaging containers. In this study, the stability of b-carotene in dehydrated DGLV samples of amaranthus (amarathus hybridus (I1)), nightshade (solanun nigrum), and cowpea leaves (vigna unguiculata) stored with oxygen absorber for a period of up to six months was investigated. Oxygen absorption within the packaging material was based on the reaction of iron (steel wool) with oxygen. The dehydration process was achieved by drying the vegetables usin solar dryers for six hours. The content of (b-carotene in the fresh samples ranged between 781.94 and 1047.45 mg/g dry matter (DM). Dehydration resulted in a loss of betweO'n 16.41 and 32.28% bcarotene. A loss of 61.4 to 81.3% was noted for samples stored under normal conditions. The content of (b-carotene was considerably higher in samples stogy under oxygen absorber at the end of storage time as compared to those stored under normal conditions ' for the three vegetables. The amount of (b-carotene was enhanced by 30% in oxygen absorber as compared to storage under ambient (normal) conditions. Under these normal conditions, the level of 0-carotene decreased gradually from dehydration stage towards the end of storage period. Samples stored under inert atmosphere showed a nearly perfect stability throughout the entire storage time while those stored under iron steel wool oxygen absorber showed a relatively high stability from the initial stages. The removal of oxygen in the storage packaging improves the retention of (b-carotene and hence its stability during storage. All the vegetable samples showed the presence of the transition metals, iron and copper ranging from 0.20 wg/g to 0.25 mg/g for iron and 1.23 NLmg/g to 1.76 mg/g for copper. Normally presence of these metal ions in vegetable samples aids in the degradation of (b-carotene by acting as catalysts in the oxidation process.