It is intended to utilize .beta.-glucan produced by a bacterium belonging to Aureobasidium sp. From a bacterium belonging to Aureobasidium sp., a mutant with little pigment accumulation is constructed by a mutagenesis means of, for example, irradiating with ultraviolet light or treating with a mutagen. A culture obtained by culturing this mutant in a liquid culture medium is usable as a composition with a large .beta.-glucan content without showing any intense dark green color caused by the accumulation of melanin-like pigments. This composition may be taken as such as a functional food having the physiologically active functions of the .beta.-glucan-containing composition. Alternatively, it may be added to foods, drinks. food additives, cosmetics and so on.