Abstract: Walnut oils were prepared by three different processes: organic solvent extraction, cold pressing and hot pressing with different roasting treatments, and their volatile compositions were determined by headspace-gas chromatography-mass spectrometry (HS-GC-MS). The difference in their key aroma components was clarified by principal component analysis (PCA) and clustering heat map analysis based on relative odor activity value (ROAV). The results showed that there were significant differences (P < 0.05) in the volatile composition of the walnut oils prepared by different processes. A total of 92 volatile substances were identified in 11 walnut oil samples, mainly including aldehydes, hydrocarbons, alcohols and oxygenated heterocycles, with trans-2-heptenal (21.00%–28.61%), n-hexanal (15.09%–20.72%) and cis-2-octene (9.77%–16.28%) being dominant in the pressed oil, while n-hexanal (35.79%), trans-2-heptenaldehyde (13.46%) and valeraldehyde (11.79%) being dominant in the extracted oil. Through PCA based on ROAVs, nonanal (fatty, citrus-like and grassy flavor), trans-2-nonanal (cucumber-like, fatty and grassy flavor), trans,trans-2,4-decadienal (deep-fat fried, waxy, and fatty flavor) and 1-octen-3-ol (mushroom-like flavor) were identified as the key aroma components in walnut oil. The clustering heat map indicated a significant color difference among the walnut oil samples prepared by different processes, indicating that it was feasible to distinguish walnut oils prepared by different processes based on volatile substances.

Key words: walnut oil; volatile substances; relative odor activity value; principal component analysis; clustering heat map