Variation in levels of vitamins a and c with maturity of amaranthus hybridus (l) leaves grown in different soil - types in Kwale County, Kenya
Otieno, Calleb Duya
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The prevalence of vitamins A and C deficiencies (VAD and VCD) in Kenya are 84 % and 45 % respectively, pointing towards health hazards among human beings. The deficiencies are mainly attributed to poverty and limited accessibility to expensive but rich food sources that contain vitamins A and C. Fruits and vegetables are however cheaper and easily available as sources of vitamins A and C. These are grown in various soils and are consumed at various stages of maturity thus being factors that present a research gap for investigation on their effect on the vitamin levels. Amaranthus hybridus L. vegetable is known to have high contents of beta-carotene (β-carotene) and ascorbic acid. In Kenya, it is grown in clay, loamy, and sandy soils of different climatic conditions including Kwale County. The mean amounts of β-carotene and ascorbic acid in the leaves of A. hybridus L. grown in clay, loamy, and sandy soils from Matuga, Msambweni, and Kinango Sub-Counties of Kwale County were investigated at different maturity stages. The levels of N, P, K, S, Mg, and Ca in the soils were determined using Flame Atomic Absorption Spectroscopy (FAAS), flame photometry, and UV-vis spectrophotometry as appropriate. The levels of ascorbic acid and β-carotene were investigated at 25, 50, and 75 days after sowing (DAS) using HPLC and UV-vis spectrophotometry respectively. Data analysis and ranking of means were done using analysis of variance (ANOVA) and Student Newman Keuls test (SNK) respectively. The range of mean levels of macro-nutrients (μg/g) in soils was: N (0.58±0.01-0.93±0.01), P (0.01±0.01-1.04±0.02), K (0.04±0.02-8.41±0.03), S (2.30±0.01-5.93±0.01), Mg (0.41±0.09-20.35±0.25) and Ca (0.04±0.06-3.81±0.20). The mean value of β-carotene (mg 100 g-1 DW) ranged from 1.63±0.14 for leaves grown in sandy soil in Matuga Sub-County at 25 DAS to 12.74±0.58 in clay soil from Msambweni Sub-County (CSMS) at 75 DAS. The mean amount of ascorbic acid (mg 100 g-1 DW) ranged from 20.79±1.62 for leaves grown in sandy soil from Kinango Sub-County (SSK) at 25 DAS to 108.11±14.94 in clay soil from Kinango Sub-County (CSK) at 75 DAS. It was found that the levels of vitamins in the leaves of the plants grown between the different soils were different. Also observed was the variation in the levels of vitamins was due to maturity of the plants as well. Findings showed that, depending on the type of soil and its macro-nutrient content, plant maturity had a significant effect on the levels of β-carotene and ascorbic acid in the leaves as the amounts of β-carotene increased significantly with maturity while that of ascorbic acid decreased (P<0.05). Specifically the leaves of the plant grown in CSMS and CSK are recommended for consumption at 75 DAS, a period that they showed the highest levels of the vitamins. It is envisaged that for soils with sufficient macro-nutrients in Kwale County, A. hybridus (L) vegetable should be consumed with consciousness based on the soil type and plant maturity inorder to adequately address the health related problems associated with VAD and VCD.