A GC-MS-based untargeted metabolomics approach for the discrimination of Haymilk and Mountain Product labelled milk

The EU market offers a range of milk types, differentiated by origin, production method, processing technology and quality. In this study, we investigated the distinction between Haymilk (HM), Mountain Product-labelled milk (MP) and milk from conventional production systems (Extended Shelf-Life conventional milk – ESL, and High-Quality conventional milk – HQ) by low molecular weight metabolomics using gas chromatography-mass spectrometry (GC-MS). The metabolite profile of the different milk typologies was shaped both by the production specifications underlying each voluntary quality scheme, including feeding regulations for HM and geographical origin restrictions for MP milk, and by the pasteurization treatment applied to raw milk prior to retail placement (standard or high-temperature pasteurization). By coupling univariate and multivariate statistical approaches with metabolic pathway analysis, some discriminant compounds, related to specific metabolic routes (particularly those involved in carbohydrate and energy metabolism), were observed to contribute to the differentiation among retail milk typologies. Particularly, myo-Inositol, scyllo-Inositol, fucose, fructose and glucose resulted up-regulated in HM compared to ESL while some amino acids and organic acids, such as isoleucine, alanine, serine, 2-hydroxyglutaric acid and orotic acid appeared down-regulated in MP compared to HQ. Overall, these findings confirm that different retail milk typologies are characterized by distinct metabolic profiles, supporting previous evidence, and providing additional insight into the biochemical differences associated with production systems and quality labels in the dairy sector.