Physical, chemical, and nutritional quality parameters of three different types of oil: determination of their reusability in deep frying

Deep frying is the process of immersing food in hot oil at a temperature of approximately 180°C. During deep frying, different chemical reactions are taking place, resulting in changes in the physicochemical properties of the frying oil, eventually leading to harmful health effects on the consumers. Nevertheless, based on economic feasibility, both the domestic and industrial levels tend to repeatedly use edible oils for deep frying. Thus, the current study aimed to evaluate physicochemical and nutritional parameters of commercially available coconut oil, palm oil and sunflower oil and to investigate the effect of repeated deep frying for the physicochemical and nutritional parameters of the studied oil samples. Thereby, the optimum number of frying cycles for each type of oil was also investigated. In order to achieve that, using coconut, palm and sunflower oils, potato and fish were fried separately for five repeated frying cycles. As per the results, regardless of the frying material, the relative density, colour, peroxide value, free fatty acid value of coconut oil, palm oil, and sunflower oil were increased significantly with increase the number of frying cycles whereas the smoke point and moisture content was found to be significantly decreased. In contrast, the number of cycles suitable for repeated frying is varying upon the frying material. Accordingly, coconut oil has proven to be used for three frying cycles of potato and five frying cycles of fish: palm oil for one frying of potato and two fryings of fish without adversely altering their physicochemical and nutritional properties. Conferring to the obtained results, the use of unsaturated oil like sunflower oil on repeated frying is not recommended.