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Minor components, especially antioxidative constituents, play an imperative role in the nutritional and health impact of edible oils. Traditionally made edible vegetable oils that are unrefined are good sources of natural antioxidants, vitamin E, and polyunsaturated fatty acids which are very important for human health. Polyphenolic compounds naturally present in oils have antioxidant activity and protect the organism against cardiovascular and degenerative diseases. Polyphenols, as thermally unstable compounds, are usually removed from edible oils during various refining processes. The antioxidant potential of polyphenols depends of the type of polyphenol compounds and their ability to give a hydrogen atom from hydroxyl groups and stabilize the phenoxy radical formed by delocalization of free electron within aromatic structure. The oils included in the study were refined and virgin oils of sesame, groundnut, coconut, sunflower and palm oils. The aim of the study was to determine the total phenolic content and antioxidant activity of the selected oils. The results showed that the total polyphenol content for virgin oils ranged from 19.8 to 50.13 mg GAE/100g and for refined oils were in the range of 8.1 to 45.16 mg GAE/100g respectively. The results showed that the antioxidant activity for virgin oils ranged from 28.00 to 63.81 AAEAA/100g and for refined oils were in the range of 14.00 to 32.56 AAEAA/100g respectively. The total polyphenol and DPPH radical scavenging activity of refined oils significantly changed (P<0.05) after refining process. However, chemical refining hardly affected the total polyphenol content and antioxidant activity. The results showed that the refining process had the greatest impacts on bioactive minor components of refined oils.
Keywords: Antioxidant activity, total phenol, refined, cold processing, vegetable oil.