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Native Spearmint Oil
Singh et al. (1990) determined that the effect of drying and storage of spearmint leaves prior to distillation for a period of greater than 20 days in India resulted in a reduction of the carvone content of oil produced from such leaves from 72.6% to 66.3%.
Adamovic (1993) reported that the carvone content of commercially available spearmint oil produced in Serbia during the years 1981–1990 ranged from 53–78%.