Effect of Frying Temperature and duration on the Formation of Trans Fatty Acids in Selected Fats and Oils
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Trans fatty acids occur in food either naturally or produced during heat processing of food containing unsaturated fats. Naturally occurring trans fatty acids have different physiological and biological functions as compared to those formed in heat processed food which increase the risk of coronary heart disease. The aim of this study was to investigate the effect of heat treatments [heating temperature: 120, 150, 190 and 250°C and heating period: 10, 30, 60 and 180 minutes] on the amount of trans fatty acids (as elaidic acid) of fat and oil samples [two solid-state (margarine and ghee) and two liquids-state (olive oil and corn oil)]. Results showed that elaidic acid content in margarine was not affected by heat at 120°C at all studied heating durations. At 150, 190 and 250°C, there is a cubic significant relationship between elaidic acid content and time of heating. Elaidic acid content in ghee was not affected by heat treatment at 120°C, while at 150°C, there was a cubic significant relationship between elaidic acid content and heating time. At 190°C, there was a negative linear relationship between elaidic acid content and time of frying, while at 250°C, there was oscillatory relationship in the amounts of elaidic acid with time of heating. As a conclusion, all margarine and ghee samples analyzed in this study had elaidic acid before and after heat treatment used in the study. However, corn oil and olive oil were free from elaidic acid before and after studied heat treatments. Therefore, it is recommended to cook and bake with vegetable oils (such as corn oil) instead of solid fats, and to keep margarine and ghee consumption as low as possible in nutrition.