Abstract
In this study, flaxseeds roasted at microwave (MW) powers of 180, 360 and 540 W for 5 and 10 min were evaluated for their influence on oil yield, chemical properties, carotenoid and chlorophyll contents, total phenolic content (TPC), radical scavenging activity (RSA), oxidative stability index (OSI), fatty acid composition and Maillard reaction products (MRPs). MW roasting at 540 W for 10 min significantly increased the oil yield, TPC, OSI, RSA, a* value, browning index, carotenoid and chlorophyll contents while decreased the L* and b* values of flaxseed oil (FSO). MRPs were detected only in oil of flaxseeds roasted at 540 W for 10 min. The level of stearic, palmitic, oleic, linoleic and α-linolenic acids were slightly changed and FTIR spectra showed minor variation in peak intensities of oils from different MW roasted flaxseeds. MW roasting (540 W for 10 min) is recommended for improving quality and stability characteristics of FSO.
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Key Points
The quality of oils is strongly impacted by the way oilseeds are processed. The conventional processing pre-treatments of oilseeds include dehulling, cracking, milling, flaking, roasting, steaming and enzymatic hydrolysis. The objective of applying different pre-treatments in oilseeds is to obtain desirable quality changes in the extracted oils. Numerous studies have shown that roasting treatment of oilseeds influences phenolic and pigment contents, antioxidant activity, FAs and oxidative stability of oils. Among different roasting methods, microwave (MW) roasting is simple, fast, energy-efficient and impressive method for enhancing yield and quality of oil. To optimize FSO yield and further enhance the oil quality in terms of its antioxidant potential, oxidative stability and nutraceutical properties, an appropriate time and MW power combination needs to be established. Therefore, this study evaluated the effect of MW power (180, 360 and 540 W) and radiation time (5 and 10 min) on oil yields, chemical properties, pigment content, TPC, radical scavenging activity, Maillard reaction products, oxidative stability index and fatty acid composition of FSO. The oil yield, TPC, RSA, BI, OSI, a* value, chlorophyll and carotenoid contents of FSO were increased while L* and b* values declined significantly with an increase in MW power and radiation time. The MW roasting at 540 W for 10 min resulted in the formation of MRPs and greater leaching of phenolic compounds, and pigments into the oil. The decrease in color values (L* and b* values) and increase in OSI of FSO relates with the rise in BI, pigments and formation of MRPs. The FTIR spectra of FSO showed minor changes in peak intensities which relate with changes in the level of SFA and UFA with increment in MW power and radiation time. FSO is considered as a healthy oil due to the presence of oleic, linoleic and α-linolenic acid composition. Owing to higher oil yield and improved quality characteristics, MW pretreatment at 540 W for 10 min is recommended for extracting oil from flaxseeds for various applications in the food and pharmaceutical industries.