Evaluation of the thermal history of bovine milk from the lactosylation of whey proteins: an investigation by liquid chromatography-electrospray ionization mass spectrometry.

Abstract

Reversed-phase high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (RP-HPLC-ESI-MS) has been used for analysis of the native and lactosylated forms of the main whey proteins, alpha-lactalbumin and beta-lactoglobulins A and B, in commercial bovine milk samples after different thermal treatment (pasteurisation and ultra high-temperature, UHT, treatment), of different lipid content, and of different brands, to find markers of the thermal history of the milk. A new quantification strategy was developed, based on peak-area integration after multiple ion current extraction and considering all the ions detectable in the multi-charge ESI mass spectrum for each type of protein. Validation of the procedure for native forms was first accomplished by calibration with model solutions. Linearity was always good. Sensitivity was different for alpha-lactalbumin and beta-lactoglobulins; the signal was stronger for the latter with only a slight difference between variants A and B of beta-lactoglobulins. Application of the quantification approach to pasteurised and UHT milk samples showed that the distributions of the three proteins and of their three main forms (native, and mono and bi-lactosylated) in whey extracts can be used as statistically robust discriminatory properties for recognition of commercial thermal treatment of milk.