The quality and oxidative stability of flaxseed oils of varying degrees of refinement

Flaxseed oil, a key source of plant-based ω-3 α-linolenic acid, is susceptible to oxidation and hazardous substance formation during refining and storage. This study evaluated the effects of refining stages (crude, degumming, complete refining) on aldehydes, trans fatty acids, and oxidative stability in flaxseed oil. The results indicate that heat-pressed oil has dark color with high a^⁎ and b^⁎ values, but exhibits the relatively highest oxidative stability during the oxidation process. However, compared to cold-pressing, heat-pressing promotes the generation of three additional aldehydes, butenal, nonanal, and trans, trans-2,4-decadienal. Degumming optimizes the color of crude oil while maintaining α-linolenic acid. In contrast, complete refining (degumming, deacidification, bleaching, and deodorization) caused the loss of substantial carotenoids and polyphenols, and α-linolenic acid decreased by 3.48 %–4.47 %, as well as a large amount of production of trans fatty acids. In addition, complete refining not only leads to the formation of newborn acrolein and trans-2-nominal but also results in a significant increase in most aldehydes concentration. This study provides a reference for the processing of flaxseed oil when considering the formation of hazardous substances induced by the oxidation and isomerization of polyunsaturated fatty acids.