Effects of Roasting Conditions on Volatile Organic Compounds in Roasted Walnut Kernels Based on HS-GC-IMS, HS-SPME-GC-MS and Electronic Nose

To explore the effects of different roasting conditions (roasting temperature: 100, 110, 120, 130, 140, 150 °C and roasting time: 15, 30, 60, 90, 120 min) on volatile organic compounds (VOCs) in roasted walnut kernels, the changing patterns of VOCs in Wen185 cultivar walnut kernel along with increasing roasting time and temperature were investigated via the combination of sensory evaluation, headspace-gas chromatography-ion mobility spectroscopy (HS-GC-IMS), headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), and electronic nose. Furthermore, these data were analyzed by partial least squares discriminant analysis, clustered heat maps, odor activity value analysis, and principal component analysis. The results showed that 33 and 58 VOCs were identified by HS-GC-IMS and HS-SPME-GC-MS, respectively. Moreover, the proportion of aldehydes, ketones, alcohols, and esters in walnut kernels exceeded 80% during the roasting process. With the increase of roasting time from 15 min to 120 min and roasting temperature from 100 °C to 150 °C, the proportion of aldehydes exhibited an increasing trend, while the proportion of ketones and esters decreased consistently. Alcohols proportion was relatively unchanged. Notably, roasting temperature had a greater effect on the amount of roasted walnut kernel VOCs than roasting time. In addition, the characteristic aroma substance of roasted walnut kernels was 2-methylbutyraldehyde (roasted flavor). When the walnut kernel was roasted under 120 °C for 60 min, the aroma of walnut kernel was stronger, which was better than those of roasted walnut kernels under other roasting conditions, indicating that this roasting condition was good for roasting walnut kernels. © The Author(s) 2025.