Storing monatin or a salt thereof in the presence of a radical scavenger
and/or in a UV light-shielding container is effective for preventing the
decomposition of monatin or a salt thereof by exposure to ultraviolet
light, particularly under acidic conditions. Sweetener compositions which
contain monatin or a salt thereof and a radical scavenger, a colorant,
caffeine and the like are resistant to decomposition by UV light.