Method of glycation of a polypeptide

A method of modifying by glycation a polypeptide having beta-galactosidase activity, comprising:

• contacting the polypeptide with 30-90 wt % of a reducing sugar under conditions sufficient to produce a polypeptide modified by glycation,
• wherein the reducing sugar is fructose, galactose, glucose, glyceraldehyde, ribose, xylose, cellobiose, maltose, or lactose, wherein the conditions comprise contacting the polypeptide in a solution at pH 5-8, for a time of 3-100 hours, at a temperature of 50-80° C., and wherein the polypeptide has at least 3% of lysine and arginine residues of the polypeptide modified by glycation.