Structural modification and digestibility change of β-lactoglobulin modified by methylglyoxal with the simulated reheating of dairy products.

A methylglyoxal (MG)-β-lactoglobulin (bLG) model was established to simulate reheating conditions (60-100 °C) to investigate the modification effect that α-dicarbonyl compounds had on protein structure and on the digestibility of milk protein. The results showed that bLG can be modified by MG, and the modification degree increased with the increase in reheating temperature. The reacted lysine and arginine as well as the generated protein-bound N-carboxymethyllysine and N-carboxyethyllysine in the modified bLG also increased with temperature. The high-resolution mass spectrometry results revealed that the modification site is at the lysine and arginine residue of bLG. Additionally, nine types of modifications were detected, and N-carboxyethyllysine was the dominant modification product. The in vitro digestibility of MG-modified bLG clearly decreased with the increase in reheating temperature. This result was consistent with the degree of structural modification and could be explained by the specific action sites (lysine and arginine) of the digestive enzyme, which were modified by MG.