The reductone ingredient is preferably ascorbic or isoascorbic acid, a salt of ascorbic or isoascorbic acid, such as an alkali metal or alkaline earth metal salt, an ester of ascorbic or isoascorbic acid, 6-O-palmitoyl ascorbate, ascorbyl phosphate, 2,3-dihydroxy-2-propenal and hydroxypropanedial.