Indirect determination of Amadori compounds in milk-based products by HPLC/ELSD/UV as an index of protein deterioration

The determination of the Amadori compounds in raw (whole), pasteurized, UHT cow milks and dietetic infant formulas (DIF), as a consequence of Maillard reaction, was performed by high performance liquid chromatography with evaporative light scattering and ultraviolet detections (HPLC/ELSD/UV). In these milks and milk-based products damage caused by heat treatment could increase as a result of storage conditions and manufacturing processes that alter their content in protein. Protein damage was indirectly evaluated by measuring the furosine content, that revealed values ranging from 9.7 +/- 0.2 to 138.0 +/- 6.2 mg per 100 g of protein in raw cow and UHT milks, respectively, and between 51.5 +/- 1.8 and 448.3 +/- 23.5 mg per 100 g of protein for fresh commercial powder milk and stored during two years at room temperature, respectively. DIF revealed levels of furosine ranged from 21.4 +/- 0.8 to 81.5 +/- 2.9 mg per 100 g of protein depending of the protein source and DIF composition. ELSD response does not depend on the sample's optical characteristics and the sample components are detected with nearly equivalent response factors. The furosine content is a good indicator to evaluate the extent of the Maillard reaction and can be used in order to calculate the decrease of bioavailable lysine. In some DIF, protein damage greatly reduces the beneficial effects as a dietary supplement. (C) 2004 Elsevier Ltd. All rights reserved.