Ascorbic acid content in leaves of Nightshade (Solanum spp.) and spider plant (Cleome gynandra) varieties grown under different fertilizer regimes in Western Kenya

This journal article, published in the African Journal of Biotechnology on Feb. 17, 2016, was co-authored by Emmanuel Ayua, Violet Mugalavai, James Simon, Stephen Weller, Pamela Obura and Naman Nyabinda.

Introduction

Sub-Saharan countries are endowed with a variety of nutrient-dense African indigenous vegetables which are traditional vegetables with edible shoots, flowers and young leaves. In Kenya, black nightshade, spider plant, and amaranthus are the most commonly consumed indigenous vegetables. African Nightshade (S. nigrum) is a highly valued indigenous vegetable, often cooked for its flavorful and perceived healthy benefits. For instance, black nightshade leaves can help manage diabetes, high blood pressure, anemia, peptic ulcers, colds, coughs and sight problems. Spider plant (Cleome gynandra), also known as cat whiskers, are frequently served as a side dish, herb or as a tasty relish. 

Hunger, micronutrient deficiencies and childhood malnutrition remain perennial problems in African developing countries and this is due, in part, to low vegetable consumption. Consequently, African indigenous vegetables production and consumption can be used to alleviate these food insecurity and micronutrient deficiencies. 

Abstract

Vitamin C is an important micronutrient because of its antioxidant and health promoting properties. With the introduction and commercialization of improved African indigenous plants, few studies have examined the impact of leaf age or the nutrient status of the plants by fertilizer. This study sought to determine amounts of vitamin C using redox titration in mature and immature leaves of spider plant (Cleome gynandra) and black nightshade (Solanum spp.) grown in fields and subjected to various sources of fertilizers which were chicken manure to provide an organic source, Mavuno fertilizer to provide a conventional synthetic source and no fertilizer to serve as a control. Chicken manure led to the highest (167 mg/100 g) vitamin C content which was however not statistically significant from Mavuno fertilizer (150 mg/100 g) at P≤ 0.05 in the nightshade variety. The highest vitamin C with no fertilizer application was 105/100 g and 79 mg/100 g in SS-49 and UG-SF varieties respectively. Moreover, vitamin C content was highest in mature leaves than in immature ones whatever the kind of fertilization treatment applied. By recognizing the impact of leaf age and importance of providing adequate fertilization, farmers can produce higher yielding and more nutritious leafy greens.