Deciphering lipase-catalyzed lipolysis in milk at low temperatures based on intelligent sensory, volatile compound, and lipid profiles.

The addition of lipase enhances milk flavor. However, the lipolysis metabolism in milk, particularly at low temperatures, remains poorly understood. This study presents the first comprehensive investigation into the effects of lipase treatment (4 °C, 0-6 h) on the sensory characteristics, volatile compound profiles, and lipid composition of milk. Facial expression analysis and sensory evaluation demonstrated that lipolyzed milk generated happiness due to enhanced fat aroma and creaminess, while increased bitter and astringent notes were associated with mild feelings of sadness and disgust. Analyses based on relative odorant activity value (ROAV), partial least squares-discriminant analysis (PLS-DA), and random forest (RF) models identified hexanoic acid, heptanoic acid, octanoic acid, 2-heptanone, 2-pentadecanone, and delta-dodecalactone as key volatile compounds formed during lipolysis. Lipidomic analysis showed the breakdown of glycerides (TGs and MGs), glycerophospholipids (mainly PEs), and sphingomyelin released free fatty acids (FFAs), serving as precursors for flavor development. During lipolysis, saturated fatty acids in the molecular chains were preferentially hydrolyzed to release FFAs that enhanced aroma, whereas polyunsaturated fatty acids tend to undergo oxidation, forming aldehydes and ketones. This study demonstrates the potential to improve milk flavor through low-temperature lipase treatment and elucidates the associated lipid profile changes during lipolysis.