Vitamin C contents of tropical vegetables and foods determined by voltammetric and titrimetric methods and their relevance to the medicinal uses of the plants
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Date
2010-01-31
Authors
Ogunlesi, M.
Okiei, W.O.
Azeez, L.
Obakachi, V.
Journal Title
Journal ISSN
Volume Title
Publisher
International Journal of Electrochemical Science
Abstract
Vitamin C contents measured as ascorbic acid, in thirty-eight samples of tropical leafy vegetables and foods were determined by two methods. One was by cyclic voltammetry using glassy carbon, Ag/AgCl and platinum electrode system in 0.1M phosphate buffer, pH 2.0 containing 1mM Na2EDTA in a potential range of 200 mV – 1000 mV using a scan rate of 50 mV/S. The anodic peak current for the electrochemical oxidation of ascorbic acid to dehydroascorbic acid was recorded at 580 mV. The other method involved titration of aqueous mixtures of the samples using N-bromosuccinimide. Samples identified to be rich in vitamin C include red pepper (123.73 mg/100 g) and the leaves of white camwood (211.20 mg/100 g), climbing black pepper (181.19 mg/100 g), curry plant (140.50 mg/100 g), fluted pumpkin (129.39 mg/100 g), amaranth globe (97.49 mg/100 g) and jute mallow (serrated edge, 89.94 mg/100 g). Boiling of aqueous mixtures of some vegetables reduced the vitamin C content by 20-43%. The results obtained by both methods were comparable for several samples but were appreciably different for some green leafy vegetables. The data in this report further enlarge the database of vitamin C contents in tropical fruits and vegetables which are sparse in literature and will serve as a useful guide in the selection of plants which are rich in vitamin C. The relevance of the vitamin C contents with medicinal uses of some of the plants is discussed
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Keywords
Vitamin C , cyclic voltammetry , N-bromosuccinimide , Tropical leafy vegetables