Minerals and Nutrient Variations as Influenced by Harvesting Stages in selected African Leafy Vegetables Grown in Busia, Kenya

Abstract

Proper nutrition contributes to declines in under-five mortality rates and improves the productivity of adults. Addressing nutritional problems requires adequate information on the diets of individuals and populations. African leafy vegetables (ALVs) are widely consumed and often harvested at different stages after planting. Four ALVs namely Vigna unguiculata, Amaranthus hybridus, Cleome gynandra and Solanum scabrum are commonly grown in western Kenya, their potentials have not been evaluated for supply of nutrients. However, nutritional values may vary depending on the species and harvesting stage. The effects of harvesting stages on nutritional value of selected ALVs were evaluated. The trials were laid out in a randomized complete block design in three replicates. Leaves were sampled at different harvesting stages and analyzed for N, P, K, Na, Ca, Mn, Mg, Fe and Zn levels. The levels of nutrients significantly (P≤0.05) varied between species and harvesting stages. The Fe, Mg and Zn levels were above the Recommended Dietary Allowance. Amaranthus hybridus had higher (P≤0.05) levels of P, Ca, Zn, Mn and Na. The N, P, K, Ca and Zn levels significantly (P≤0.05) increased from 4 to 6 weeks after seed emergence (WAE) then decreased from 6 to 10 WAE. The Fe levels increased from 4 to 6 WAE while the increase from 6 to 10 WAE was not significant. Magnesium levels significantly (P≤0.05) increased from 4 to 8 WAE then decreased, while Mn and Na levels did not vary with harvesting stage. Harvesting the ALVs from 4 to 6 WAE for the supply of P, K, Ca and Zn, 4 to 8 WAE for Mg and 4 to 10 WAE for the supply of Na and Mn is recommended.