Antioxidant content of various oils following reaching smoking point.

Abstract

Background: Antioxidants are potent reducing agents which inhibit the oxidative process by neutralising or preventing the formation of reactive oxygen species. To better understand the beneficial effects of antioxidant compounds in the chosen oils it is important to investigate whether these bioactive compounds differ in extra virgin or refined types and how heating influences its level. Objectives: To measure the antioxidant content of oils before and after reaching the smoking point. To measure the total polyphenol content of oils before and after reaching the smoking point. To identify the smoking points of oils. Methods: The antioxidant capacity of different oils is determined using the ferric reducing antioxidant power (FRAP) method. The total phenolic content is determined using the Folin-Ciocalteau colourimetric method. The smoking point of each oil is measured by sugar thermometer. Results: Mean antioxidant and polyphenol levels of all oils after reaching the smoking point were higher than before heating. Antioxidant level was higher before heating only for extra virgin olive oil. The total polyphenolic content was higher before heating for extra virgin olive oil, extra virgin coconut oil and coconut oil. Rapeseed oil showed the highest antioxidant level of all oils both before and after cooking what indicates a strong thermal stability. Extra virgin coconut oil showed the lowest antioxidant level of all oils both before and after cooking. Extra virgin olive oil showed the highest polyphenolic content of all oils before and after cooking. The highest smoking point had rapeseed oil and the lowest the extra virgin rapeseed oil. Conclusion: Significant differences in antioxidant and polyphenolic contents were found between oils before and after reaching the smoking point. A strong positive correlation was found between FRAP values and total phenolic content, p < .0005. The mean total antioxidant and polyphenol levels were higher after heating the samples. This suggests that health benefits from antioxidants can be obtained even after reaching smoking point. Key Words: antioxidants, polyphenols, smoking point, oils, FRAP, Folin-Ciocalteau method.