Roasting Time Shapes Quality Attributes, Aroma Formation and Oxidative Lipid Remodeling in Almond Oil

Roasting time strongly influences almond oil yield, flavor and oxidative stability. This study investigated almond oils obtained by pressing almond kernels roasted at 130 °C for 0, 5, 10 and 20 min, corresponding to cold-aroma, light-aroma, strong-aroma and sauce-aroma groups, respectively, by combining physicochemical analysis, fatty acid quantification, gas chromatography-ion mobility spectrometry (GC-IMS), machine learning and lipidomics. Increasing roasting time enhanced oil yield from 45.81% to 50.34%, with no further significant increase after 10 min. Stronger roasting moderately reduced the free radical level. In contrast, acid value, peroxide value and thiobarbituric acid reactive substances (TBARS) increased from 0.28 to 0.38 mg KOH/g oil, 1.20 to 1.46 meq O₂/kg oil and 0.38 to 0.46 mg malondialdehyde/kg oil, respectively, indicating limited oxidative deterioration. Fatty acid analysis showed that oleic acid remained relatively stable at 644.37-647.03 mg/g oil, whereas linoleic acid decreased significantly from 150.42 to 140.19 mg/g oil. GC-IMS detected 59 volatile signals and clearly separated the four processing groups, indicating substantial roasting-induced changes in volatile fingerprints. A positive-unlabeled (PU) learning model used 27 literature-supported aroma-active compounds as the positive class and 32 compounds without confirmed aroma-activity evidence as the unlabeled class. The model showed good cross-validated discrimination, with a mean area under the receiver operating characteristic curve (ROC-AUC) of 0.866 and a mean area under the precision-recall curve (PR-AUC) of 0.756, and prioritized eight unlabeled compounds, mainly alcohols and methional, as candidate aroma-active compounds requiring further sensory validation. Lipidomic analysis showed that accelerated oxidation caused broad lipid remodeling, with 327 differential lipids between cold-aroma oxidized and unoxidized oils, mainly involving glycerophospholipids, glycerol lipids, sphingolipids and fatty acyls. Overall, increasing roasting time improved oil recovery and promoted aroma differentiation while causing only limited initial oxidative deterioration, providing a theoretical basis for optimizing roasting conditions in industrial processing.