Phytochemical and antioxidant analysis of gynandropsis gynandra subjected to different cooking methods

Abstract

Gynandropsis gynandra is one of the common vegetables that serves both the nutritional and therapeutic role. However, it is usually consumed when cooked and there is insufficient scientific research providing information on the effects of cooking on the bioactive compounds present in this vegetable. This study was undertaken to quantitatively evaluate the phytochemical composition and antioxidant activity in cooked leaves of G. gynandra. The leaves of G. gynandra were subjected to boiling and steaming for 15 and 30 minutes each. The antioxidant activity, vitamin C and beta-carotene content in the cooked leaves was estimated and compared with the amount present in the raw leaves. Vitamin C content was estimated by volumetric analysis using standard DCPIP solution and the highest amount was found in the raw leaves, containing 721.1mg/100g. Boiling and steaming reduced the vitamin C content in the leaves to 158.4mg/100g and 566mg/100g respectively, but there was less reduction of vitamin C in the steamed leaves. Beta-carotene was extracted with 95% ethanol at 60oC and determined by successive shaking with 85% ethanol and petroleum ether in a separating funnel. The amount of beta carotene was highest in the leaves steamed and boiled for 15 minutes with 4550±70.70μg/100g and 4090±127.30μg/100g respectively and lowest in those cooked for 30 minutes. The antioxidant activity of the cooked leaves was determined using DPPH radical scavenging method. The leaves boiled for 30 minutes exhibited the highest antioxidant activity with percentage inhibition of 63.41±0.73% and the lowest percentage inhibition was in the raw leaves with 44.32±1.46%. Steaming is the best cooking method for nutrient retention. This study encourages that this vegetable should be steamed for 15 minutes before consumption. This is of medicinal significance because the amount of bioactive compounds present after cooking can still perform their free-radical scavenging activity, hence important in preventing and reducing risk of chronic diseases.