Characterization of volatile organic compounds in walnut oil with various oxidation levels using olfactory analysis and HS-SPME-GC/MS
Lina Sun, Guowang Wang, Lijian Xiong, Zhongqiang Yang, Yan Ma, Yanlong Qi, Yongyu Li
Abstract
Walnut oil oxidizes and becomes rancid during storage, that could be significantly affecting flavor and quality. This study aimed to monitor the volatile compounds present in walnut oil during storage, identify the characteristic markers of walnut oil at different oxidation levels, and establish a correlation network analysis based on the relationship between the olfactory analyzer and the characteristic markers to understand their correlation. The results indicated that the oxidation level of walnut oil had a positive correlation with the response of the olfactory analyzer. 219 volatile compounds were identified in walnut oil, with 89 identified as key volatile compounds (VIP >1). Among these, compounds such as (E, E)-2,4-decadienal (6.10%–23.04%)，(E, E)-2,4-heptadienal (2.23%–13.61%)，(E)-2-octenal (0.95%–11.71%)， hexanoic acid (1.63%–4.30%)，1-octen-3-ol (2.53%–19.01%)，(Z)-2-heptenal (5.95%–25.01%)，2,3-dihydro-furan (1.08%–3.20%)，2-pentyl-furan (0.13%–0.54%), pyrazine (0.33%–1.32%), hexanal (24.52%–1.33%)，3-hethylbutylacetate (12.44%–1.29%)， 2-methyl butyl acetate (7.74%–1.56%) and ethenyl hexanoate (4.39%–0.41%) were found to be characteristic volatile compounds in the oxidation process of walnut oil. Furthermore, the correlation network analysis revealed a strong correlation between the olfactory analyzer sensors and the characteristic volatile compounds. The findings of this study can provide valuable data for the development of rapid determination of the oxidation level of walnut oil. • Identify volatile compounds in walnut oil with different oxidation levels using an HS-SPME-GC/MS and olfactory analyzer. • E-nose analyses showed significant differences between the content of volatile compounds in walnut oil with varying oxidation levels. • The HS-SPME-GC/MS technique identified 219 volatile compounds, 89 of which were the key volatile compounds (VIP>1). • 13 essential flavor compounds were screened during the oxidation process, defined as the characteristic volatile compounds. • The olfactory analyzer strongly correlates with the volatile compounds determined by HS-SPME-GC/MS.