ANTIOXIDANT PROPERTY OF BIOACTIVE COMPOUND
Antioxidant compounds in natural products play an important role as a health protecting factor. Scientific evidence suggests that antioxidants reduce the risk for chronic diseases. Most of the antioxidant compounds are derived from plant sources and belong to various classes of compounds with a wide variety of physical and chemical properties. The main characteristic of an antioxidant is its ability to trap free radicals. Highly reactive free radicals and oxygen species are present in biological systems from a wide variety of sources. Antioxidant compounds like phenolic acids, polyphenols and flavonoids scavenge free radicals such as peroxide, hydroperoxide or lipid peroxyl and thus inhibit the oxidative mechanisms in nucleic acids, proteins, lipids or DNA and can initiate degenerative disease. It has been proposed that the antioxidant properties of phenolic compounds can be mediated by the following mechanisms (Cotelle, 2001):
(1) Scavenging radical species such as Reactive Oxygen Species (ROS)/ Reactive Nitrogen Species (RNS).
(2) Suppressing ROS/RNS formation by inhibiting some enzymes or chelating trace metals involved in free radical production.
(3) Up regulating or protecting antioxidant defense.
Due to the chemical diversity of phenolic compounds and the complexity of composition in plant samples, it is difficult and inexpensive to separate each phenolic antioxidant and study it individually. Moreover, study of total antioxidant power of a complex sample is often more valuable because of the cooperative action of antioxidants. Therefore, it is desirable to standardize convenient screening methods for quick quantification of antioxidant property of phenolics in natural products. A variety of antioxidant assays such as Trolox equivalent antioxidant capacity (TEAC), oxygen radical absorbance capacity (ORAC), total radical-trapping antioxidant parameter (TRAP), ferric ion reducing antioxidant power (FRAP) and cupric ion reducing antioxidant capacity (CUPRAC) assays have been widely used for quantification of antioxidant capacity of phenolic samples from fruits and vegetables. The Folin-Ciocalteu antioxidant capacity assay (F-C assay, or total phenolics assay) is also considered as another antioxidant capacity assay because its basic mechanism is as oxidation/reduction reaction though it is used as a measurement of total phenolics content (Huang et al., 2005).
In the early 80’s, the search for natural antioxidants was given emphasis and several natural sources were examined. Many phytochemicals that are antioxidants, have been isolated from extracts of different parts of M.oleifera and J. curcas , such as seeds, fruits, leaves, stems, and roots (Malecka, 2002; Schmidt et al., 2003). It is reported that a purified bioactive compounds (phenolics) from M.oleifera and J. curcas wastes are with highest antioxidant activity having free radical inhibition activity (Shrikhande, 2000; Muthuswamy et al., 2008; Tuchila et al., 2008). The free radical inhibition activity in the peels of oranges, lemons, pears as well as yellow and white flesh nectarines were found to contain twice the amount of total phenolic compounds than that of the pulp of these fruits (Gorinstein et al., 2001). Example peels of peach (Chang et al., 2000), pomegranate (Li et al., 2005), apple (Wolfe and Liu, 2003), grapes (Torres and Bobet, 2001), mango (Ajila et al., 2010) contain more antioxidant activity than the whole fruit. Other than peels even seeds of longans, avocados, jackfruits and tomato are reported to have higher antioxidant activity than that of the edible product (George et al., 2004; Soong and Barlow, 2004). Acerola fruit extract and citrus plants agro industrial waste were also evaluated to have antioxidant activity (Shukla et al., 2009; da Silva Caetano et al., 2011). Antioxidant activities have also been reported from leaves of Piper betle (Islam et al., 2010).
