Effects of different cooking methods on bioactive compound content and antioxidant activity of water spinach (Ipomoea aquatica)

Abstract

Water spinach (Ipomoea aquatica), green leafy vegetable, belongs to the morning glory family (Convolvulaceae). It is a commonly found in Vietnam and other tropical countries and rich source of phytochemical compounds. Recent studies have reported that water spinach has inhibitory effects against prostaglandin synthesis, liver diseases, eye diseases, and constipation, and has an oral hypoglycemic effect in healthy subjects. Water spinach extract has also been found to alleviate antioxidant‐related disorders, reduce blood sugar, and protect against nosebleed and high blood pressure. Water spinach is usually boiled or steamed, or eaten fresh when prepared as soups. This study aims to determine the effects of different cooking methods (fresh, boiling, and steaming) on total bioactive compounds and evaluate the in vitro antioxidant activity in 80% ethanolic extracts of water spinach by spectrophotometric methods. We identified the best extraction solvent and compared the effects of different cooking methods on phytochemical contents and antioxidant activity of water spinach. Steamed water spinach extracted with 80% ethanol had the highest amounts of 35.0 mg/g total chlorophylls, 7.1 mg/g carotenoids, 35.6 mg/g total polyphenols, and 40.4 mg/g total flavonoids. The steaming process showed higher antioxidant activity than the uncooking or boiling process. The 80% ethanol extract showed a higher level of antioxidant activities than the water extract. The antioxidant activity was measured with the DPPH, ABTS, hydroxyl and superoxide anion racial scavenging assays as well as the reducing power activity assay were increased in a concentration dependent manner. The overall results support that water spinach contains bioactive compounds and they may play a positive role in our health.