Forms and Bioavailability of Zinc and Copper Essential Elements in Parts of Watermelons from Ngara and Mwea Markets, Kenya
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During the last few decades analytical chemists and nutrition scientists have increasingly realized that total concentrations of chemical elements cannot give, in general, information about mobility, bioavailability, and the eventual impact of elements on biological organisms. Only the knowledge of the chemical species of the elements can provide an understanding of chemical and biochemical reactions, bioavailability, and subsequent paths of metabolism, thus leading to more information about essentiality or toxicity. This stresses the necessity of speciation analysis to determine the species of an element in a specific matrix. There is need therefore to determine the species of essential elements in different types of fruits, vegetables and other foods. One fruit that is increasingly being consumed and which is available throughout the year and has essential elements is watermelon (Citrullus lanatus (Thunb.) Matsum and Nakai). There is need to determine the form in which the essential elements occur in the seed, red flesh, white flesh and peel in a watermelon to avoid deficiency when used as food to encourage use of thrown away parts. The study therefore aimed at providing information on bioavailability and forms of essential elements in the peel, white flesh, red flesh and seed parts of watermelons. Water and ethanol extractable elements are more available for absorption than those extracted by other solvents. Watermelons selected for the study are widely consumed and were purchased from Mwea and Ngara markets in Kenya. They were separated to peel, seed, white and red flesh and dried. Each of the watermelon part was sequentially extracted with hexane, dichloromethane, ethanol, water and lastly residue digested and Flame Atomic Absorption Spectrometry (FAAS) was used to determine the levels of each element in various fractions. Free Zn2+ and Cu2+ ions and their organic acid complexes in the extracts constitute the bioavailable forms. The data of this study were analysed through One Way Analysis of Variance. The results of this study showed that there were variations in extracted mean levels of Zn and Cu minerals in the parts and varieties of watermelon. Significantly high water extracts mean levels (p < 0.001) of 0.46±0.01 mg/100 g, (46%) Cu was recorded in peel of sugar baby from Ngara market compared to the other watermelon samples. Crimson sweet watermelon samples bought from Ngara market recorded the highest Zn water extracts mean levels (p < 0.001) of 4.84±0.04 mg/100 g, (52%) in red flesh compared to the other watermelon varieties in the market. Charleston grey watermelon samples from Mwea market significantly recorded a high Zn water extracts mean levels (p < 0.001) of 5.96±0.01 mg/100 g, (61%) in white flesh than was recorded in the other parts of the watermelon varieties. Presence of hexadecanoic and octadecanoic acids which are complexing agents that enhance bioavailability of Zn and Cu were obtained in the watermelon extracts through GC - MS analysis. The bioavailable species of Zn and Cu could have been either as free ions or their organic acid complexes. Since Zn and Cu minerals were bioavailable in the four parts of the watermelon samples, people should eat all the parts of watermelon either when dry or fresh as a source of these nutrients. Result from this study will be used to guide people on nutrition aspect of a watermelon which will in turn enhance human health.