Potential toxicity of some traditional leafy vegetables consumed in Nyang’oma division, western Kenya

Abstract

Traditional leafy vegetables are those plants whose leaves or aerial parts have been integrated in a community’s culture for use as food over a long span of time. These vegetables are highly recommended due to their relatively high nutritional value  compared to the introduced varieties, and are also important in food security. Qualitative phytochemical screening, using  standard laboratory procedure, was carried out for alkaloids, saponins, cardenolides, flavonoids and polyphenols on traditional  leafy vegetables consumed amongst the Luo, an agro-pastoral community living along the shores of lake Victoria, Western  Kenya. The vegetables were: Amaranthus hybridus L. (subsp.hybridus), Asystasia mysorensis T. Anderson, Coccinia grandis (L) Voigt, Crotalaria ochroleuca (Kotschy) Polhill, Cucurbita maxima Duchesne ex Lam, Portulaca quadrifida L., Sesamum calycimum Welw. var. angustifolium (Oliv.) Ihlenf. and Siedenst., Senna occidentalis L. and Sida acuta Burm. F. All the vegetables were found to contain polyphenols and flavanoids while other classes of phytochemicals varied from species to species Brine shrimp lethality tests  revealed that S. calycimum var. angustifolium (LC₅₀ 84.8 μg/ml), S. occidentalis (LC₅₀99.5 μg/ml), S. acuta (LC₅₀ 99.4 μg/ml), C. grandis (LC₅₀  100.6 μg/ml) and A. mysorensis (LC₅₀ 207.7 μg/ml) exhibited marked levels of toxicity. C. ochroleuca (Sunnhemp) contained all the five classes of  phytochemicals, but proved less toxic (LC₅₀ 4511.3 μg/ml). This vegetable is highly utilized in Nyang’oma, and seventy per cent of the respondents consume this species. A. hybridus (African spinach, or Amaranth) was found to be the least toxic (LC₅₀ 6233.6 μg/ml) and this vegetable is recommended for consumption. From the results, five vegetables contain possible agents that can cause acute or chronic toxicities when consumed in large quantities or over a long period of  time. Hence some vegetables should be consumed with great care. Though further studies are required to determine which of the phytochemicals are lethal to mammals.

Key words: Traditional vegetables, phytochemicals, toxicity, Luo, Nyang’oma