Insight into the microwave pretreatment of rapeseeds on the flavor characteristics of rapeseed oils

Microwave heating is a new technique employed for the pretreatment of rapeseed oil (RO) and can vary RO flavor with different processing time. This study investigated the flavor characteristics of RO from microwaved rapeseeds with different processing time using scanning electron microscope (SEM), electronic nose (E-nose) and two-dimensional gas chromatography coupled with headspace solid-phase micro-extraction and mass spectrometry (HS-SPME-GC × GC-MS). SEM results show that microwave pretreatment induced cell swelling and disintegration, forming a creased surface of rapeseeds. E-nose found that W1W, W1S, W2W and W5S were the main sensors to distinguish the RO flavors. HS-SPME-GC × GC-MS detected a total of 333 volatile compounds with 105 key aroma compounds in ROs. The longer microwave pretreatment, the more volatile compounds formed, especially heterocyclic compounds and glucosinolate degradation compounds. In general, ROs were classified as: 0–3 min of green and woody flavors, 4–6 min of oxidized flavor and 7–10 min of smoky, roasted and pungent flavors. Microwave of 4–6 min was considered as the transitional state from 0-3 min to 7–10 min, and 10 min was regarded as an overheated sample distinguishable from other ROs.