Time-resolved volatile profiles and molecular-species lipid remodeling during lipase treatment of anhydrous milk fat

Enzymatic lipolysis is an established approach for modifying dairy flavor, yet the molecular-species lipid state associated with process-stage changes in aroma remains incompletely resolved. In this study, nine commercial lipases were compared under a unified apparent activity, and A12 was selected for detailed evaluation across a six-point hydrolysis time course (0-90 min) based on sensory screening. Sensory analysis combined with headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) was used to characterize volatile evolution, while untargeted lipidomics compared the 0- and 30-min states. A12 treatment generated a sensory-favorable intermediate state at 30 min, characterized by high aroma harmony and balanced dairy attributes. HS-SPME-GC-MS tentatively identified 50 volatile features showing compound-specific temporal behavior. Methyl ketones exhibited nonuniform dynamics, with 2-heptanone showing a transient peak at 15 min, 2-tridecanone decreasing relative to the control, and 2-nonanone remaining relatively stable at early stages before declining. Aldehydes such as hexanal displayed a late-stage increase, while other volatiles followed distinct trajectories. HS-GC-IMS detected 76 signal features and revealed platform-dependent responses, including divergent trends for 2-heptanone between the two analytical systems. Lipidomics annotated more than 1000 molecular species and revealed nonuniform depletion of triacylglycerols accompanied by enrichment of diacylglycerols, monoacylglycerols, and free fatty acids, particularly those containing medium-chain and unsaturated acyl groups. These findings define the molecular-species lipid profile of a 30-min sensory-favorable processing state in A12-treated anhydrous milk fat. The main contribution of this work is the process-state-level integration of lipid molecular-species remodeling with dual-platform volatile fingerprints, showing that HS-SPME-GC-MS and HS-GC-IMS provide complementary but non-interchangeable views of volatile evolution. Rather than demonstrating direct biochemical conversion pathways, the results provide a structured framework for describing how lipid molecular remodeling coincides with volatile-profile changes in enzyme-treated dairy fat systems and highlight the need for targeted quantitative and isotope-resolved studies for mechanistic validation.