Abstract

Cleome gynandra, a leafy vegetable consumed among all age-groups, is often limited by its inherent bitter taste due to the chemical compound, proanthocyanidins (PAs), commonly known as condensed tannins (CT), located in the vegetative parts of the plant. Therefore, a study was conducted during 2017 at Green Biotechnologies Research Centre of Excellence (GBRCE), University of Limpopo, South Africa to determine the optimum harvesting time and PAs concentration level in C. gynandra leafy vegetable, unsuitable for consumption purposes. Pre-chilled C. gynandra seeds were directly sown in 20-cm-diameter plastic pots filled with 10,000 cm3 mixture of steam pasteurised loam soil and Hygromix-T growing media at 3:1 v/v. Pots were placed on greenhouse benches at an inter- and intra-row spacing of 20 cm and irrigated to field capacity with 250 ml of chlorine-free tapwater. Irrigation was then scheduled for every other day. Harvesting time viz., 4, 6, 8, 10 and 12 weeks represented treatments, while week 4 served as control. The study was arranged in a completely randomised design, in triplicates. Harvested material from each treatment was oven dried at 60°C for 24 hrs prior to PAs chemical analysis (Butanol-HCl method). The generated relationships were modelled through the regression curve estimates from the quadratic equation (Y = b2x2 + b1x + c), to obtain the optimum harvesting time and PAs concentration. Harvesting time had highly significant (P≤0.01) effect on PAs concentration of C. gynandra tender shoots and leaves. Treatments contributed 99% of the total treatment variation in PAs concentration of the harvested material. Optimum harvesting time was achieved at 9 weeks after planting, with optimum PAs concentration of 89%. Therefore, for consumption purposes, harvesting of C. gynandra leafy vegetable should be done between week 4 and week 9 after planting, when PAs concentration is not at peak.