Phenolic compounds in plant oils: A review of composition, analytical methods, and effect on oxidative stability

Phenolic compounds from different plant sources, like fruits, vegetables, cereals, and herbs, have been excessively studied and widely used in different industrial areas, including food, medicine, and pharmaceuticals. Recently, special attention has been paid to the phenolic compounds of plant oils that have recently been found to vastly affect the oxidative stability of these products. This paper reviews the contents and types of phenolic compounds in their initial forms in plant oils and methods of their determination. Also, their impact on the oxidative stability of oils is discussed. The total free content of phenolic compounds and the phenol profile in plant oils are very diverse and depend on the oil source and production method. Generally, the main oily source of these compounds is rice bran and olive fruits. Their high amounts can also be found in rapeseed, flaxseed, grapeseed, and pumpkin oils. The main groups of phenolic compounds in oils are phenolic acids and flavonoids. Additionally, lignans, secoiridoids, and phenolic derivatives are identified in some oils. The two main methods for the determination of phenolic compounds in oils include the spectrophotometric and chromatographic ones. The general principles of these assays are often modified by various authors to adapt them to research conditions. Available literature data confirmed the strong antioxidative activity of some phenolic compounds found in oils. However, further studies are needed to better understand the mechanism of their protective action on oils, especially under natural storage.