INTRODUCTION
Processing methods are known to have variable effects on total phenolic compound and antioxidant activity of plant samples. Effects include little or no change, significant losses, or enhancement in antioxidant activity (Nicoli et al., 1999). Food processing can improve the properties of naturally occurring antioxidants or induce the formation of new compounds with antioxidant activity, so that the overall antioxidant activity increases or remains unchanged (Tomaino et al., 2005).
Antioxidants present in vegetables are very useful and beneficial to health and have been associated with reduced risk of cardiovascular diseases and various forms of cancer (Kumud et al., 1990). These benefits have led to research studies in order to find antioxidants in plant material mainly used as foods (Yang et al., 2008). Among the compounds with antioxidant properties are the phenolics, which are believed to act as antioxidant, anti-carcinogenic, anti-microbial, anti-allergic, anti-mutagenic and anti-inflammatory, as well as in the reduction of cardiovascular diseases (Vali et al., 2007). Phenolics occur naturally in plants and are present in fruits, vegetables, leaves, nuts, seeds and flowers; therefore, they are present in the human diet, but are also used in some medicinal preparations (Madrau et al., 2008).
Onions (Allium cepa Linn) is used as foodstuff, condiments, flavouring agent, and in folk medicine (Ola-Mudathir and Maduagwu, 2014). It has been extensively studied for their therapeutic uses as antibiotic, antidiabetic, anti-atherogenic and anticancer (Augusti, 1996). It has been found that administration of onion products to diabetic rats significantly reduced hyperglycaemia (Kumud et al., 1990). Biological action of Allium products is ascribed to organosulfur compounds, which have also been shown to possess antioxidant and free radical scavenging activities. Onions have previously been shown to protect testis against cadmium induced oxidative stress in rats (Ola-Mudathir et al., 2008). Keeping this in mind, many studies have reported losses in total phenolic content (Ismail et al., 2004; Roy et al., 2007; Toor and Savage, 2006). These losses in antioxidant property of heat-treated samples were attributed to the leaching of phenolic compounds into water (Larrauri et al., 1997) as well as other methods of food processing. However, there still remains paucity of information on the effect of different processing methods on the antioxidant status of onions which is essentially used for the preparation of delicacies as well as in the preparation of decoctions used by trado-medical practitioners for treatment of some ailments. There is however a few reported studies on the effect of domestic processing on the antioxidant potentials of onions. Such information would be more relevant considering the fact that onions are rarely consumed raw without processing. Common processing methods include: remover of the outer layer, chopping into smaller pieces before boiling, grilling or flying in oil. Several cultures also subject onions to sprouting for the purpose of using the shoots as vegetables. After sprouting, the onions bulbs are usually discarded while the shoots are processed further. These usually discarded onion bulbs may have antioxidant potentials resulting from sprouting. These improved properties could be harnessed to combat or manage some degenerative and non-communicable diseases.
1.1      AIM OF STUDY
This study is geared towards determining the effects of sprouting and boiling on the antioxidant potentials of onions (Allium cepa L.).
           The Specific Objectives Are: