Protein lactosylation in UHT milk during storage measured by Liquid Chromatography-Mass Spectrometry and quantification of furosine

The initial stage of the Maillard reaction, protein lactosylation, occurs during heat treatment of milk and continues during subsequent storage. We compared the initial lactosylation as well as the rate of lactosylation of milk proteins during storage in UHT milk subjected to direct or indirect heat treatment using liquid chromatography (LC) coupled with electrospray injection mass spectrometry (ESI-MS). Furosine content was used as an overall marker to allow for a quantitative correlation of lactosylation measured by LC-ESI-MS in the UHT milks. Protein lactosylation increased during the storage period of 6months at 20 degrees C. Both the initial extent and the rate of lactosylation positively correlated with the number of lysine residues in the different proteins. An exponential or linear correlation with furosine concentration could be established for major and minor lactosylated proteins, respectively.