Phansawan and Poungbangpho (2007) studied the antioxidant capacities of five different medicinal plants; Pueraria mirifica, S. rebaudiana Bertoni, Curcuma longa Linn., Andrographis paniculata (Burm.f.) Nees. and Cassia alata Linn. The method was based on inhibition in absorption of ABTS (2,2′-azinobis(3-ethylbenzothiazolline-6-sulphonic acid) technique and the antioxidant capacity was recorded as TEAC. The medicinal plants were subjected to extraction with five solvents including ethanol, methanol, acetone, acetic acid, and distilled water, where the highest antioxidant capacity was found in S. rebaudiana Bertoni, followed by C. alata Linn. and C. longa Linn. A. paniculata (Burm.f.) Nees. and P. mirifica had the lowest antioxidant capacity. The highest antioxidant capacity was found in S. rebaudiana Bertoni extracted with acetone and methanol, followed by S. rebaudiana Bertoni extracted with ethanol, and C. alata Linn. extracted with ethanol, and the lowest antioxidant capacity was found in Andrographis paniculata (Burm.f.) Nees. extracted with acetone.
Stevia leaf extract exhibits a high degree of antioxidant activity and has been reported to inhibit hydroperoxide formation in sardine oil with a potency greater than that of either dl-α-tocopherol or green tea extract. The antioxidant activity of Stevia leaf extract has been attributed to the scavenging of free radical electrons and superoxides ( Thomas & Glade, 2010). A recent study assessing the in vitro potential of ethanolic leaf extract of S. rebaudiana indicates that it has a significant potential for use as a natural antioxidant ( Shukla, Mehta, Bajpai, & Shukla, 2009).