Phenolic acid composition of flaxseed cultivars by ultra-performance liquid chromatography (UPLC) and their antioxidant activities: Effect of sand roasting and microwave heating

Six flaxseed cultivars were studied for their antioxidant activity (AOA), total phenolic content (TPC), reducing power, and metal chelating activity after being subjected to sand roasting and microwave heating. Various phenolic compounds from methanol extracts were identified and quantified using ultra-performance liquid chromatography (UPLC). Both roasting and microwave heating significantly (p < .05) affected the antioxidant properties of flaxseed. A significant (p < .05) increase in AOA, metal chelating activity as well as reducing power of flaxseed was observed after heat processing. The results revealed that microwave heating resulted in significantly (p < .05) higher decrease and a higher increase in TPC and reducing power, respectively, as compared to sand roasting. UPLC data revealed the presence of 10 phenolic compounds namely: Ellagic acid, catechin, chlorogenic acid, gallic acid, Kaempferol, umbelliferone, Caffeic acid, coumaric acid, epicatechin, and rutin. The most abundant phenolic constituent was Ellagic acid whose concentration varied significantly among control and various heat processed flours. Practical applications The present study was undertaken to investigate separation and quantification of phenolic compounds in different flaxseed cultivars and their corresponding antioxidant activity after subjecting them to sand roasting and microwave heating. There are no published papers on quantification of phenolic compounds in flaxseed by UPLC as influenced by heat-processing methods. This work has shown that heat processing significantly influence the antioxidant properties of flaxseed. Microwave heating might be successfully employed as an innovation tool for flaxseed so as to develop minimally processed flaxseed to be used in different food and nonfood industries.