Effect of infrared ray roasting on oxidation stability and flavor of virgin rapeseed oils

Abstract

Effects of infrared ray roasting (IRR) on the oxidation stability and flavors of virgin rapeseed oil (VROs) at 110−170°C were investigated and compared with traditional roller roasting (TRR). Results showed that IRR samples showed lower acid and peroxides values, higher oxidation stability index, and 2,2‐diphenyl‐1‐picrylhydrazyl radical scavenging activity than TRR ones. IRR samples displayed better thermal expansion of rapeseed for internal fragmentation from microstructures, which facilitated the release of tocophenols (652.63−748.78 mg/kg) and 4‐vinylsyringol (7.54−678.19 mg/kg), compared with TRR ones with tocophenols (652.63−689.28 mg/kg) and 4‐vinylsyringol (7.54−524.18 mg/kg) contributing to better oxidation stability. Moreover, important volatile compounds, including pyrazines, isothiocyanates, nitriles and aldehydes, were formed quantitatively more in IRR than TRR samples, which was attributed to better heat transfer efficiency and internal fragmentation promoting complex reactions inside rapeseed. Therefore, IRR has more positive roasting effects on VROs than TRR. Practical Application Virgin rapeseed oil is a massively consumed flavor vegetable oil, but the traditional high‐temperature roller seed roasting process can cause serious quality problems. Our work applied a novel roasting technology, infrared ray roasting to rapeseed pretreatment. The results show that this new type of roasting technology is more efficient and stable and has important applications in the production of virgin rapeseed oil with better oxidative stability and flavor.

Lipid oxidation in fragrant rapeseed oil: Impact of seed roasting on the generation of key volatile compounds

“… Zhou et al (2019) reported that the hexanal, heptanal, (E)-2-hexenal, benzaldehyde, and (E,E)-2,4-decadienal were identified as key volatile compounds in commercial FROs. These products have also been observed in the work of Yu, Wang, Zhang, Liu, and Li (2021) . The majority of aldehydes reported in rapeseed oil have to do with the fatty flavor, but some lead to green, nutty, or rancid odors as well ( Zhang et al, 2021 ).…”

“…FRO is mainly processed by cleaning, roasting, physical pressing, and centrifugation or filtration ( Yu, Wang, Zhang, Liu, & Li, 2021 ). Among these steps, the complex reactions that occur during roasting are essential for creating flavor compounds in FROs during processing ( Yang et al, 2022 ).…”

A novel infrared roasting to improve the flavour profile of virgin rapeseed oils

“…Based on an investigation of local oil industries, the optimum roasting temperatures of TRR are within 150–170 °C (Yu et al ., 2021). In the pre‐experiment, VROs were determined to better flavour profile at 150–170 °C.…”

“…Therefore, temperatures of TRR were set from 150 to 170°. The samples were heated using a traditional roller roasting machine (Jiangsu Maisi Machinery Equipment Co., Ltd., Wuxi, Jiangsu) at 150–170 °C for 20 min (Yu et al ., 2021). A handheld digital temperature probe was used to measure temperature.…”

“…Moreover, Yu et al . (2021) have reported that 4‐vinylsyringol and tocophenols were increased from 7.54 to 678.19 mg kg −1 and 652.63 to 748.78 mg kg −1 during roasting, respectively. Therefore, roasting should be considered for higher VRO quality.…”