PROXIMATE CONTENT AND ANTIOXIDANT PROFILE OF PUMPKIN (Cucurbita pepo L.) LEAFY VEGETABLE AS INFLUENCED BY NPK FERTILIZER

Abstract

This study evaluated the influence of NPK fertilizer on the proximate content and antioxidant profile of pumpkin leafy vegetable. The vegetable was raised at the Teaching and Research Farm, Obafemi Awolowo University, Nigeria in 2010 for two seasons and the following NPK fertilizer rates were applied: 0, 50, 100, 150, 200 and 250 kg/ha and replicated six times. Six composite samples from the six replications were analyzed in duplicates for proximate content and antioxidant profile. For the antioxidant assays, crude extract was obtained from cold extraction of each of the samples with 80% methanol and evaporated to dryness. The hydrogen donating or radical scavenging of the extract was determined using the stable radical DPPH (2, 2-diphenyl-2-picrylhydrazyl hydrate). Total phenol content was determined by the method of Singleton and Rossi using the Folin – Ciocalteau reagent in alkaline medium while total flavonoid content was determined using AlCl3 method as described by Lamaison and Carnet. The proanthocyanidin content was determined using a modified method of Porter et al, using the AlCl / Butan – 1-0l assay method while the total anthocyanin content of the test samples was determined using the pH differential method of Fuleki and Francis as described by Guisti and Wrolstad. Crude protein, Carbohydrate, Ash, Crude fibre, Ether extract (fat) and Moisture contents were determined using the routine chemical analytical methods of Association of Official Agricultural Chemists (AOAC). The chemical compositions analyzed were reduced significantly when fertilizer rate exceeded 100 kg NPK/ha. The proximate values in pumpkin leaves are 23.8, 0.18, 1.65, and 2.16 g/100g for protein, fat, ash and crude fibre respectively. Fertilizer rates from 150 – 250 kg/ha reduced these values by 10 – 40%. With the increase in fertilizer rates from 100 kg – 250 kg/ha, antioxidant activities was reduced by 19%, phenol by 57% and flavonoid by 65%. For the food value and bioactive compounds of pumpkin to be retained, NPK fertilizer application should not exceed 100 kg/ha if it must be applied.