Sun-drying of green leafy vegetables is popularly practised in many homes in Nigeria, as a way of preserving green leafy vegetables for future use. This project sought to investigate the effect of this method of preservation of vegetables on the antioxidant phytoconstituent (Vitamin C and Total phenol) and activity (reducing property and free radical scavenging ability) of some commonly consumed green leafy vegetables in Nigeria namely Structium sparejanophora (Ewuro-odo), Amarantus cruentus (Atetedaye), Telfairia occidentalis (Ugu), Baselia allia (Amunu tutu), Solanum macrocarpon (Igbagba), Corchorus olitorius (Ewedu), Vernonia anygdalina (Ewuro) and Occimum graticimum (Efinrin). The edible portions of the green leafy vegetables were sun-dried for seven days before determining the Vitamin C and total phenol content, as well as the reducing property and free radical scavenging ability. The result of the study revealed that sun-drying of green leafy vegetables cause a significant (P < 0.05) decrease in the Vitamin C content (16.67-64.68% loss). Conversely it leads to a significant increase in the total phenol content (6.45-223.08% gain), reducing property (16.00-362.50% gain) and free radical scavenging ability (126.00-5757.00% gain) of the green leafy vegetables. It could therefore be concluded that a significant decrease (P < 0.05) in Vitamin C content caused by sun- drying will not reduce the antioxidant activity of the green leafy vegetable, moreover, the phenol constituent of the green leafy vegetables contributes more to the antioxidant properties of vegetables than ascorbic acid, as its increase on sun-drying cause a significant (P < 0.05) increases in the antioxidant properties of the green leafy vegetables, irrespective of the decrease in the ascorbic acid content.

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Maize varieties (yellow and white) were roasted for 17 min; and allowed to cool, and later milled into powder. The nutritional evaluation (proximate composition, mineral and antinutrient content determination) and antioxidant properties investigation (reducing power, free radicals scavenging ability and Fe 2+ chelating ability) of the product was subsequently carried out. The result of the study revealed that roasting caused a significant increase (P < 0.05) in the crude fat, carbohydrate, Ca, Na, Mg and Zn content. Conversely, a significant decrease (P < 0.05) was observed in crude protein, crude fibre, Fe and K content. A significant decrease in the phytate content was also observed. However, the reduced phytate content did not have sparing effect on Zn bioavailability. Roasting significantly (P < 0.05) reduced the extractible phenol and flavonoid content of the maize varieties. The antioxidant properties (1,1-diphenyl-2-picrylhydracyl free radical scavenging ability and Fe 2+ chelating ability) followed the phenolic content pattern. However, roasting caused a significant increase in the ferric reducing antioxidant power of the maize varieties. Thus, roasting reduced the protein content of maize but also increased the energy value and antioxidant capacity as exemplified by high reducing power.

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The effect of fermentation on the polyphenol distribution and antioxidant activity of four underutilized legumes [Cajanus cajan L. Millsp (Pigeon pea), Vigna subterranea L. Verdc (Bambara groundnut), Sphenostylis stenocarpa Harms (African yam bean), and Phaseolus vulgaris L. (Kidney bean)] were investigated. The beans were cooked (12 h), soaked in boiled water (12 h), dehulled, and then cooked again (2 h). The cotyledons were drained, wrapped in jute sacks and left to ferment at 37°C (4 days) to produce condiments. The distribution of free and bound phenolic compounds in the fermented and unfermented beans was determined; thereafter the free radical scavenging ability, reducing power, and the ability of the free and bound phenolic compounds of the fermented and unfermented beans to inhibit lipid peroxidation were determined. The results of the study revealed that fermentation caused a significant increase (p<0.05) in the free soluble phenol content of the legumes, while there was a significant decrease (p<0.05) in the bound phenol content of the legumes. Free soluble phenol from both the fermented and unfermented legumes had a significantly (p<0.05) higher reducing power (except C. cajan), free radical scavenging ability (except C. cajan) and inhibition of lipid peroxidation than bound phenolic extract. However, free soluble phenolic compounds from the fermented beans had a significantly higher (p<0.05) reducing power, free radical scavenging ability, and inhibition of lipid peroxidation than free soluble phenols from unfermented beans. Hence, it was concluded that, fermentation could increase the free soluble phenolic content of the underutilized legumes tested and consequently enhance the antioxidant activities of the legumes; fermented V. subterranea was found to be the most promising condiment with antioxidant activity.

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