Phytosterols in edible oil: Distribution, analysis and variation during processing

Phytosterols, which are naturally occurring in plants, have excellent nutritional and health values on lowering both the blood cholesterol level and the risk of cardiovascular diseases. Edible oils are the main source of daily intake of phytosterols, whereas the properties of phytosterols may vary a lot depending on their sources. During the processing of edible oil including refining and frying, phytosterol's content fluctuates, which influences the properties of the final product. Phytosterols and their derivatives undergo physical migration between different phases and chemical conversion during the processing, which reduces the quality and the commercial value of edible oils. Therein, the loss of phytosterols is the major concern in the process of neutralization and deodorization. In addition, oxidation and thermal degradation of phytosterols occur simultaneously during frying, which also reduces the content of phytosterols. Nevertheless, the oil matrix has a promoting or an inhibitory effect on the thermal oxidation of phytosterols. Therefore, various efforts have been devoted to analyzing and improving the remaining contents of phytosterols in edible oil. Regardless of the processing method, temperature plays an important role in the loss of phytosterols. At present, the main analysis methods of phytosterols include gas chromatography and liquid chromatography, in which the pretreatment of different types of phytosterols is also a crucial step. This review focused on the following topics comprehensively: (i) the distribution of phytosterols in the oil-containing plants and edible oils during the refining processing; (ii) the pretreatment and analysis methods of various phytosterols (free phytosterols, phytosteryl fatty acid esters, phytosteryl glycosides and acylated phytosteryl glycosides); (iii) the variation of phytosterols in process of esterification and oxidation, storage and so on. The study also proposed that the investigation in the loss and safety of phytosterols during processing of the vegetable oils should be proceeded further in combination with efficient and accurate chromatography methods.