Decoding flavor formation in recombined milk: The role of milk fat fractions from dry fractionation and their fatty acid profiles

To investigate the impact of milk fat fractions on recombined milk flavor, six samples including liquid and solid fractions obtained at 25 °C (25L-M, 25S-M) and 30 °C (30L-M, 30S-M), unfractionated milk fat (MF-M) and skim milk control (skim-M), were analyzed by comprehensively employing sensory evaluation, electronic nose, and gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Liquid fractions exhibited stronger milky and sweet aromas than solid fractions and skim control. Seventy-four volatiles were identified, with 40 odorants detected by GC-O. Furthermore, aroma-active compounds (AACs) were quantified using external calibration (21 AACs, flavor dilution, FD≥8) and stable isotope dilution analysis (9 AACs, FD≥16 and odor activity values, OAV≥1). Twelve key AACs were confirmed, with nonanal and octanal identified as the main contributors to the fatty aroma, and γ-dodecalactone and δ-decalactone were primarily responsible for the sweet aroma. Fatty acid profiling and correlation analysis supported a dual-pathway formation mechanism, with medium- and short-chain saturated fatty acids correlating with lactones, and unsaturated fatty acids (C18:1, C18:2) correlating with aldehydes and alcohols. This study clarified the molecular mechanisms of flavor regulation by milk fat fractions, providing a theoretical basis for developing flavor-optimized dairy products. • Dry fractionation creates milk fat fractions with distinct flavor-forming potentials. • Twelve key AACs were identified in recombined milk with dry-fractionated fat fractions. • A dual-pathway mechanism transforms fatty acids to odorants via cyclization and oxidation routes. • The aroma metabolism map of recombined milk guides flavor-directed dairy design.