THE EFFECT OF COOKING ON THE ASCORBIC ACID CONTENT OF SOME NIGERIAN FOODSTUFFS AND THEIR CONTRIBUTION TO VITAMIN C STATUS OF THE CONSUMERS

Abstract

In Nigeria, fresh fruits like oranges, guava, mango etc. and leafy vegetables like 'sokoyokoto’ (Celosia argentea L), ' tete ' (Amaranthus spp. L), ‘gbure’ of ascorbic acid (AA.) but these fruits are fast becoming more popular as cash crops and their consumption is falling among the lower income group, people, who now depend on vegetable consumption for their supply of vitamin C, Oke (1968). In order to be able to establish the concentration of the AA content of Nigerian edible vegetables, the effects of two most common cooking systems were investi-gated since most Nigerian leafy vegetables are subjected to heat treatment before consumption. Eighteen commonly eaten vegetables were bought from three principal markets in Ibadan i.e. Mokola, Dugbe and Orita-merin markets. Theso vegetables were Celosia argentea L - green and red (sokoyokoto). Amaranthus spp. L(Tete), Crasocephalum crepidioides B (Ebolo) Basella alba L (amunututu), Talinum triangulare J (gbure), Hibiscus esculentus L (Ila), ochorus oliturius (Ewedu), Solanum gilo radi L (Igbagba/Igbo) Vernonia amygdalins D (Ewuro), two varieties of Capscucum annum L (Atarodo' and 'Tatase'). four varieties of Capscicum frutescens L (‘fresh shombo', dry ‘shombo’, fresh 'ata wewe' and dry ‘ata wewe’), Lycopersicum esculentum M (Tomato) and Allium ascalonicum L (Alubosa), Samples of each vegetable bought from the various markets were thoroughly, mixed together. Two types of common cooking systems were adopted. These were: 1) The gasfire/aluminium pot cooking system, and 2) The firewood/claypot cooking system. The vegetables were grouped into five according to the treatment each one was traditionally subjected to. For each vegetable stew preparation there were equal number of sample replicates corresponding to the number of cooking stages during the stew preparation. Samples were taken for AA analysis at each stage of stew preparation and for each vegetable in each group during their preparation into stew using the two cooking symptoms earlier referred to. Reheating of these stews was also done as practiced in moat homes and the effect of this reheating on the AA content of this vegetable stew was also determined. Vegetables such as Amaranthus spp. L (tete) lost completely their AA content during parboiling. The sauce comprising pepper, tomatoes, onions, etc finally contributed some AA to the finished stew. Very little vitamin C was found left in some of the cooked vegetable stews such as tete stew with 0.05mg AA/gm. After reheating, only some vegetable stew samples such as ‘Gbure’ and ‘Euodu’ stews had any AA left. A dietary survey was conducted at Osegere Village near Ibadan to find the contribution if any, of the vegetable stews to the AA nutrition of Osegere Village. It was found that the amount of AA derived from vegetable stews ranged from 0 to 6.0mg per day. Out of the 102 subjects surveyed only 11 subjects had up to their normal AA recommendation using as standard, the recommendations of the Department of Health and Social Security (1969). Biochemical estimations were carried out to estimate AA levels in the blood, plasma and leucocytes of the villagers out of the 28 subjects who volunteered and went through the biochemical estimations, only 10.7% (i.e 3 subjects) had up to normal plasma ascerbate levels. The normal records used for classification are according to Paker et al (1968). However, despite the tissue ascerbate levels, none of the subjects had clinical symptoms of scurvy such as swollen gums, bleeding gums, loosening teeth etc. This implies that some Nigerians can adjust to low tissue ascerbate levels or that the international standard against which their values were compared relatively high.