Improving the thermostability of β-lactoglobulin via glycation: The effect of sugar structures

This work studied the effects of sugar structure (size, position of carbonyl group, and charge state) on the thermostability of β-lactoglobulin (β-lg) when controlling the glycation extent of reducing sugars to the same level. Ribose, glucose, maltose, maltotriose, fructose and galacturonic acid were selected to react with β-lg at aw of 0.53 at 45 °C for different periods to reach an average degree of saccharide attached per protein molecule β-lg (average DSP) of 5. β-Lg and the conjugates in pH 3, 5 and 7 were heated. The denaturation temperature was detected by differential scanning calorimeter (DSC), and the solubility was determined by Bradford assay. The results showed that all the conjugates exhibited higher denaturation temperature than β-lg. Larger molecular size, ketose and negative charge had significant effects on increasing the denaturation temperature. β-Lg and the conjugates at pH 3 and 7 could maintain their solubility when increased the temperature from 60 to 90 °C. The conjugates showed better thermostability than β-lg at pH 5 and sugar structure had effects on the improvement. Glycation by sugars with increasing size and negative charge stabilized β-lg. Ketose glycation did not show better thermostability than aldose, but caused more aggregates during mild or short time heating.