A composition containing L-arginine and a glycosyl compound of formula (I): in which R is a moiety formed of a monosaccharide, a disaccharide, or an oligosaccharide including three to five monosaccharides; and the composition contains the glycosyl compound and L-arginine in a molar ratio of 1:1.6 to 1:3.0. Also disclosed is a method for preparing such a composition, as well as a composition prepared by the method.