The Stabilising and Chelating Effects of Green and Roasted Coffee Extracts

Oxidation might be regarded as one of the most important reaction in oils and fats. Prooxidants namely iron and copper intensify and catalyze the oxidation while the chelating agents might retard or delay this process. Citric acid, phosphoric acid, some of phenolic compounds and phospholipids are considered as the compounds that chelate the prooxidant metals and through this mechanism stabilize the oil. Coffee extract, due to the nonenzymatic browning reactions during roasting of coffee and the resultant products might play an important role in the chelation of metals. The object of this research work is to study the chelation power of the coffee extracts on the stability of oils and fats. Two types of coffee; Arabica and Robousta, both green and roasted were selected for this study. Isopropanol was employed as a solvent to obtain the extract. Peroxide value determinations and induction period measurements using Rancimat apparatus, measuring the secondary oxidation products were employed as means to evaluate the chelating power of coffee extracts at 0.15% concentration and compared to citric acid a well known chelating agent at 0.01% concentration. It was concluded that both roasted and green coffee extracts due to the presence of phenolic compounds in the green beans exhibited antioxidant activity but the extracts were deficient in chelation of metals particularly copper.