Effect of storage and cooking time on the antioxidant properties of two commonly used ghanaian vegetables

Abstract

Green leafy vegetables are good sources of antioxidants. This study was designed to evaluate the effect of storage and cooking time on the antioxidant properties of two commonly used Ghanaian vegetables: Corchorus olitorius and Solanum macrocarpon locally known as "adeimey" and "gboma" respectively. The storage conditions were: Left to stand overnight at room temperature, refrigerated for one day and refrigerated for one week, and cooked for ten and thirty minutes at 100°C. The reducing power and the total carotenoid content were determined by measuring absorbance using a Shimadzu UV-120-02 spectrophotometer at 700nm and 450 nm respectively. The free radical scavenging activity was determined by the 1, 1-diphenyl-2-picrylhydrazil (DPPH) method. The antioxidant activity (AOA) ranged from 91.59 to 38.42%. The total carotenoid content (TCC) varied from 5.10 to 27.30 mg/100 g. The reducing power ranged from 9.52 to 50.59%. The results show that Solanum macrocarpon and Corchorus olitorius are good sources of antioxidants with the later exhibiting higher antioxidant properties than the former. However the AOA, TCC and reducing power decreased drastically when the vegetables were refrigerated for one day and one week and cooked for thirty minutes at 100°C. Similarly the AOA, TCC and reducing power decreased slightly when the stored vegetables were cooked for ten minutes. These findings suggest modification in the storage and cooking practices of these green leafy vegetables to ensure retention of antioxidants for the best nutritional value and health benefit. The results also indicate that in areas where refrigeration is not possible, vegetables can be left overnight at room temperature to preserve the antioxidants in them. © Maxwell Scientific Organization, 2012.