PURPOSE: To enable quick and sure determination of the presence of a specific isozyme of lipoxytenase in beans, by detecting the bleaching of β-carotene.

CONSTITUTION: The presence of a specific isozyme Lx in 3 kinds of isozymes (L1, L2 and L3) of lipoxygenase existing in ordinary beans is detected by the following process. A reaction system containing all lipoxygenase isozymes and a substrate is added with all lipoxygenases excluding the lipoxygenase isozyme Lx to be determined and the mixture is maintained under optimum condition. The presence of the lipoxygenase isozyme Lx can be determined by the occurrence of bleaching of β-carotene.