Disclosed is an adjuvant for improving the bioavailability of bioactive compositions. The adjuvant is prepared from a byproduct of mint flavor production. In vitro and in vivo testing confirms effectiveness. The adjuvant contains a mixture of compounds which is effective to improve the oral bioavailability of a bioactive composition normally having limited absorptivity, and it comprises a mixture of nonpolar compounds and compounds with some polar characteristics. In preferred form the nonpolar compounds comprise compounds selected from a group that includes terpene hydrocarbons and terpene derivatives and the compounds with some polar characteristics comprise compounds selected from a group that includes aldehydes, alcohols and ketones. The preferred compositions will have a ratio of nonpolar compounds and compounds with some polar characteristics is within the range of from 5:1 to 20:1. The adjuvants can enhance delivery of CoQ10 and other bioactive compositions, such as carotenoids (e.g., β-carotene), curcuminoids, lycopene, resveratrol, flavonoids and other phenolic compounds, organosulfur compounds, saponins, sterols, stanols, and mixtures of at least two of these, to the interior cellular environment, including organelles, such as the mitochondria.