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Vegetables and fruits have been used as natural remedies to enhance human health as they may aid in reducing the risk of getting many age-related degenerative diseases (Amin & Tan, 2002; John & James, 2005; Lee et al, 2007). In NaturalNews.com, Leigh stated that vegetables provide the body with an added source of antioxidants that is needed to combat against free radicals. According to Lu and Foo, plants are important sources of natural antioxidants. They produce different kind of antioxidant compounds to counteract Reactive Oxygen Species (ROS) in order to survive. ROS which include free radicals such as superoxide anion radicals (O2-), hydroxyl radicals (OH) and non free-radicals species such as H2O2 and single oxygen (O2) are various forms of activated oxygen (Huda-Faujan, Noriham, Norrakiah and Babji, 2007).
These free radicals are highly reactive and unstable compounds in the body during normal metabolic functions or present in the external environment in the form of pollution and cigarette smoke. Free radicals damage the cells within our body that are important to a youthful appearance and good health. Human bodies are protected from oxidative damage free radicals through complex defence system called antioxidants (Sharipah, Sunalti, Norizan, Faridahanim and Rohaya, 2009). Antioxidants slow the effects of aging. Consuming fruits and vegetables can slow down the loss of muscle elasticity that leads to wrinkle, will increase the immunity that make us less susceptible to illness and puts breaks on memory failure, as free radicals injure the brain cells for retaining information. (Norshazila, Syed Zahir,Mustapha, Aisyah and Kamarul, 2010).
Antioxidant compound reacting with free radicals, chelating, catalytic metals, and also by acting as oxygen scavengers. Currently available synthetic antioxidants such as butylated hydroxy anisole (BHA), butylated hydroxyl toluene (BHT), tertiary butylated hydroquinon and gallic acid esters, have been suspected to cause negative health effects. Hence, strong restrictions have been placed on their application and there is a new trend to substitute them with naturally occurring antioxidants (Barlow S.M. as cited in Kumar, S. Et al, 2007).
Antioxidants were first applied in industrial use two centuries ago to protect materials such as rubber from degradation process, and were later introduced to preserve foods and oils to extend shelf life. It was only 60 years ago that its significance in human physiology was recognised. But doctors were so busy battling diseases that, until recently, the protective role of antioxidants have not been fully appreciated. There are superabundance of antioxidants in our foods, chiefly found in fruits and vegetables. The more coloured and pigmented, the richer the antioxidant property. The American Cancer Society recommends at least five servings of fruits and vegetables per day to prevent cancer. Dr C.S. Foo (2010) stated that expectation of each antioxidant to work independently like a pharmacological agent in sick patients is illogical and often produces the contradictory results. According to him, antioxidants are not drugs; they are part of the bodyââ‚¬â„¢s defence and healing system.
Pietta has written that vitamins A, C and E and carotenoids are antioxidants derived from the diet. flavonoids, are also possess antioxidant properties and may account for part of the benefits associated with the consumption of fruits and vegetables. Flavonoids are also called polyphenols; commonly occur as glycosides in plants. Heim, Tagliaferro & Bobilya stated that, as antioxidants, flavonoids have been reported to be able to interfere with the activities of enzymes involved in ROS generation (as cited in Shih P.W, Lai P.L, and Jen Hoe, 2005).
The search for antioxidants from natural sources has become popular and efforts have been put into identify compounds that can act as suitable antioxidants to replace synthetic ones. In this investigation, edible plants such as Ladies Finger (Abelmoschus esculentus), drumstick (Moringa deifera), lotus seed (Nelumbo nucifera), broccoli (Brassica oleracea) and tomato (Lycopersicon esculentum) were examined for their antioxidant levels and activities. Different types of solvent were used as the extraction solvent to extract the antioxidants present in the plants.
Antioxidants compounds present in plant extracts are multi-functional and their activity and mechanism would largely depend on the composition and conditions of the test system. Frankel & Meyer wrote that many authors had stressed the need to perform more than one type of antioxidant activity measurement to take into account the various mechanisms of antioxidant action (as cited in Shih P.W et al., 2005).
Many factors can affect the extraction of antioxidant phytochemicals from natural materials. Previous studies have reported the influence of some variables such as temperature, time, solvent-to-solid ratio and etc on the phenolic production. Solvents such as methanol, acetone, hexane, chloroform or their mixture are commonly used to extract phytochemicals from plants. They are also another vital factor affecting both extraction and antioxidant activity yield of extracts. Due to complexities of both the chemical characteristics of solvents and the diverse structure and composition of the plant materials, the behaviour of material-solvent systems were different from each other and can hardly be predicted. No single solvent could extract all the antioxidants of different polarity and solubility in a single plant (Dong Y.M, Qiushuang W.M, Leqin K.B, Jianmei J.B, & Tiejin Y, 2007).
A number of in vitro methods have been used to measure the efficiency of dietary antioxidants as pure compounds. In this study, the free radical scavenging activities of the plant extracts were followed via their reaction with the stable DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical (Shih P.W et al., 2005) and FTC (Ferric Thiocyanate) method was used to determine the amount of peroxide at the initial stage of lipid peroxidation. The method of Ottolenghi (1959) was used to determine the TBA (Thiobarbituric acid) values of the samples. The formation of malonaldehyde is the basis of the well-known TBA method used for evaluating the extent of lipid peroxidation (Susi E, Asmah R, Patimah I & Taufiq, 2002).
Therefore, the first hypothesis for this study is that different solvents have different efficacy in extracting antioxidant compounds. The role of each solvent in extracting phenolics compound will provide valuable information to scientists. The second hypothesis is antioxidant capacity of the samples is due to the present of phenolic compounds.
2.1 Aims & Objectives
The objectives of this research include:
To examine the efficiency of different solvents of increasing polarity (i.e. chlorofoam, n-hexane, acetone and methanol) on the extraction yield, and antioxidant capacity of five selected edible plants in Malaysia.
To evaluate the antioxidant capacity of the four extracts of five edible plants through free radical scavenging activity.
To verify free radical scavenging activity of edible plants using three different methods.
To provide a better understanding of the antioxidant properties of these plants and allow the identification of plants with high antioxidant activity for further investigation and development into value-added foods and neutraceuticals.
Need to rewrite this section of introduction.
Give general introduction on the topic.
General introduction on the antioxidant
what is antioxidant?properties
what is free radical?
invitro tests available
the purposes of the study and so on