Mention must be made of synergists – substances which increase the effectiveness of a primary antioxidant. Certain metallic ions such as copper and iron act as pro oxidants, catalyzing the oxidation process. Such metal ions can be sequestered or chelated by certain organic acids. They effectively contribute to lower transition metal activity. Synergists are not as effective when used alone; rather, they work best when combined with an antioxidant. Examples of such compounds are citric acid, phosphoric acid and some of their derivatives (Fennema, 1985). Synergism has been studied, not just in relation to antioxidants alone, but in relation to combinations of antioxidants, anti wear and other additives (Sharma et al., 2007). An example of a synergist used in conjunction with phenolic antioxidants is citric acid (Bennion, 1995).