Exploration of milk flavor: From the perspective of raw milk, pasteurized milk, and UHT milk

In this study, raw milk was collected from three different grades of pastures and processed by pasteurization, blending and ultra-high temperature sterilization (UHT) in a factory production line with a feed size of 10 tons. Additionally, all samples (from raw milk to UHT milk samples) were analyzed by E-nose and GC-MS. Key flavor compounds such as 2-heptanone, hexanal, nonanal, 3-methyl-butanal, and dimethyl sulfide were found. The results showed that the pastures with higher grades could help to improve the quality of milk flavor, and the heat treatment had a significant impact on the milk flavor profile. The pasteurization was effective in eliminating undesirable flavors such as hexanal (ROAV>1) resulting from the oxidation of raw milk fat, whereas the ultrahigh temperature sterilization exacerbated the oxidation of milk fat that led to the massive production of ketones such as 2-heptanone (0.9 < ROAV<1.3), which contributed to undesirable milk flavors.