Levels of selected antinutrients, vitamins and minerals in African indigenous vegetable recipes in Vihiga County of Western Kenya

Abstract

African Indigenous Vegetables (AIVs) have been recommended as the most affordable source of minerals and vitamins for African families. They can be used to alleviate micronutrient deficiencies but have been underutilized due to lack of nutrition information, leading to consumption of the lesser nutritious exotic vegetables. Vihiga County is endowed with these AIVs but cases of micronutrient deficiencies remain a challenge. The potential of these AIVs as sources of micronutrients is also limited by the anti- nutrients like phytate and oxalate they contain. These bind to some minerals in the AIVs and reduce micronutrient bioavailability. The quantification of the nutrient and anti-nutrient content of formulated AIV recipes will provide nutrition information that will promote their consumption. The aim of this study was to determine the levels of phytate and oxalates, selected vitamins and minerals in AIV recipes. The study involved leaves of the following selected AIVs: Spider plant (C. gynandra), pumpkin (C. moschata), cowpeas (V. unguiculata), Amaranth (A. blitum), Jute mallow (C. olitorius), sweet potato (I. batatas), African nightshade (S. nigrum), cassava (M. esculenta), slender leaf (C. ochroleuca), Vine spinach (B. alba) and African kale (B. carinata). The individual vegetables and their mixed formulations were divided into two groups. One group was fermented and the other unfermented. The unfermented group was divided into three portions. One portion was boiled in water, the other fried and another boiled with milk and traditional salt (lye). Their Fe, Zn and Cr content were determined using AAS, β-carotene and α-tocopherol content were determined using UV-Visible Spectroscopy. Their phytate and oxalate content were determined by HPLC. The phytate content in fermented AIVs ranged from 27.5-70.67 mg/100g and 40.0-83.44 mg/100g for unfermented ones. The oxalate content ranged from 2.62-10.17 mg/100g for unfermented and 1.56-20.36 mg/100g for fermented. The phytate and oxalate content of most fermented AIVs was significantly lower than in unfermented AIVs (p<0.05). Most AIVs boiled in water contained significantly lower phytate and oxalate levels than those fried or boiled with milk and lye (p<0.05). The β-carotene content in unfermented AIVs ranged from 2.06-10.17 mg/100g while for fermented 1.92-11.05 mg/100g. The α-tocopherol content in unfermented AIVs ranged from 5.81-17.31 mg/100g and in fermented was 4.02-13.21 mg/100g. Vitamin C content in unfermented AIVs ranged from 0.60-2.45 mg/100g while in fermented was 0.24-3.07mg/100g. Fermented AIVs contained significantly lower vitamin C than unfermented AIVs (p<0.05). Some of the fermented AIVs contained significantly lower levels of α-tocopherol than unfermented ones (p<0.05). Most fermented recipes contained significantly higher levels of β-carotene than unfermented ones (p<0.05). Fried AIVs contained significantly lower levels of β-carotene, α-tocopherol and vitamin C than boiled AIVs (p<0.05). The Fe content in unfermented AIVs ranged from 13.65-113.33mg/100g while fermented was 6.58-83mg/100g. The Zn content in unfermented AIVs ranged from 3.38-9.13mg/100g while fermented was 3.66-10.33 mg/100g. The Cr content in unfermented AIVs ranged from 0.94-9.71 mg/100g while fermented was 0.21-3.63 mg/100g. The Fe, Zn and Cr content in most fried AIVs and AIVs boiled in milk and lye were significantly higher than AIVs boiled in water (p<0.05). It is concluded that cooking reduced phytate and oxalate levels in AIVs and that fermented AIVs contained lower phytate and oxalate levels than unfermented AIVs. The AIVs cooked by different methods contained levels of minerals and vitamins that meet the RDA by World Health Organization (WHO); however, vitamin C levels were lower than the RDA. The cooked and fermented recipes provide required levels of zinc, iron, chromium, alpha- tocopherol and beta