Characterization and metabolism pathway of volatile compounds in walnut oil obtained from various ripening stages via HS-GC-IMS and HS-SPME-GC–MS

Volatile organic compounds (VOCs) of walnut oil (WO) samples obtained from 5 ripening stages were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and HS-solid phase microextraction-GC-mass spectrometry (HS-SPME-GC-MS). A total of 75 VOCs were identified in WO, of which 24 VOCs were found to be the key aroma-active compounds for WO by using odor activity values (OAVs) analysis. Based on chemometrics methods, flavor of WO samples can be characterized into three categories, i.e., early, mid-, and late stages. WO from early ripening stage had stronger green and sweet odor due to 1,8-cineole (OAV 280) and ethanol (OAV 134.5). While nonanal (OAV 181.82), (E)-2-octenol (OAV 160), and hexanal (OAV 103.78) were sources of intense fatty and oily odor in mid-ripening stage. For WO of later ripening stage, the flavor was affected by nonanal (OAV 192.28), 1-heptanol (OAV 150), heptanal (OAV 71.11) and some organic acids.