Variations in Some Minerals and Nutrients Levels in Selected African Leafy Vegetables due to Harvesting Stages and Locations of Production in Western Kenya

Abstract

The nutrition transition in developing countries has resulted in changes in diets and lifestyle habits. Such changes have led to paradoxical phenomenon where under nutrition and over nutrition coexist. This double burden is reflected in Kenyan children and adults. The Kenyan poverty incidence showed a large variation by province, with Western and Nyanza all above 45% of the population. Consequently, many people living in western Kenya suffer from nutrient deficiency diseases. Proper nutrition contributes to declines in under-five mortality rates and also improves the productivity of adults. Addressing nutritional problems requires adequate information on the diets of individuals and populations. This in turn requires reliable data on both the consumption of foods and their nutrients contents. African leafy vegetables (ALVs) are widely consumed and are harvested at different stages after planting by communities in different geographical locations. The ALVs can be a major source of the nutrients. The nutritional values of ALVs may vary depending on harvesting stage and location of production. Four ALVs (Vigna unguiculata, Amaranthus hybridus, Cleome gynandra and Solanum scabrum) are commonly grown in western Kenya, yet the potential of these ALVs have not been evaluated as possible remedy to malnutrition. The intention of this study was to assess the levels of some essential nutrients, the effect of harvesting stages and site of production on selected ALVs commonly grown in western Kenya, to guide consumption levels to supply recommended dietary allowances (RDAs) of the relevant nutrients. The trials were laid out in a randomized complete block design in three replications at each site in Busia, Kisumu and Lela. Leaves were sampled and analysed for N, P, K, Na, Ca, Mn, Mg, Fe and Zn levels. Soil pH and nutrients analyses were done to ascertain their initial levels. The levels of the nutrients significantly (P:SO.05) varied with species, location of production and harvesting stages. Amaranthus hybridus had higher (P:SO.05) levels of P, Ca, Zn, Mn and Na. The ALVs were significant contributors of Fe and Mg. Consumption of 61-118 g dry weight (DW) of each of the four ALVs for the supply of Fe and 144-472 g of Solanum scabrum for the supply ofMg is recommended to supply RDAs. The ALVs from Kisumu site had the higher (P:SO.05) levels of N, P, K, Ca, Mg and Zn, while higher (P:SO.05) levels of Fe; Mn and Na were reported in ALVs from Busia and Lela sites, respectively. The N, P, K, Ca and Zn levels significantly (P:SO.05) increased from 4 to 6 weeks after seed emergence (WAE) then decreased from 6 to lOW AE, Fe levels increased from 4 to 6 WAE while the increase from 6 to lOW AE was not significant. The Mg levels significantly (P:SO.05) increased from 4 to 8 WAE then decreased from 8 to lOW AE, while Mn and Na levels did not vary with harvesting stage. Harvesting the ALVs from 4 to 6 WAE for the supply ofP, K, Ca and Zn, 4 to 8 WAE for the supply of Mg and 4 to lOW AE for the supply of Na and Mn is recommended to yield highest levels. There is need to establish the bioavailability of the nutrients in ALVs.