Characterization of volatile organic compounds in walnut oil with various oxidation levels using olfactory analysis and HS-SPME-GC/MS

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.