Role of the Polysaccharide Content and Net Charge on the Emulsifying Properties of β-Lactoglobulin−Carboxymethyldextran Conjugates

β-Lactoglobulin (β-LG)−carboxymethyldextran (CMD) conjugates were prepared by using water-soluble carbodiimide. Three kinds of CMD differing in molecular mass (40, 70, and 162 kDa) were used to investigate the effects of different CMD contents and net charge on the functional changes in β-LG. The emulsifying properties of these β-LG−CMD conjugates were investigated under various conditions by evaluating the stability of oil/water emulsions prepared with oleic acid and the β-LG−CMD conjugates. The emulsifying ability of β-LG was greatly improved by conjugating with CMD in the acidic pH range in the presence of less than 0.5 M NaCl. After heating at 80 °C for 10 min, the emulsifying stability of the β-LG−CMD conjugates was higher than that of β-LG. It is thought that increasing the polysaccharide content and shifting the isoelectric point of β-LG to the acidic side by conjugating with CMD of a high molecular weight would be effective in improving the emulsifying properties of β-LG under unfavorable conditions.