A biochemical studies of the essential oils of Mentha japonica Makino from Nagano Pref. and Chiba Pref. have been conducted.
From the changes of the yields of essential oils and the contents of each component in the course of growing stage, the following results were obtained:
The changes of contents of the component in the oils from Nagano Pref. are similar to those of M. Pulegium and M. Gattefossei, namely in the blooming stage, pulegone was reduced to menthone.
On the other hand, in the oils from Chiba Pref., menthone was further reduced to menthol, moreover in the latter stage, menthol changed to menthylacetate.