Free radical quenching activity and polyphenols in three species of Coleus

Coleus is an important aromatic herb of the family Lamiaceae which is routinely grown as a traditional medicinal herb in India. We examined the total content of polyphenols, tannins, flavones and flavonols, their antioxidant and lipid peroxidation inhibition properties in leaf and stem tissues of three species of Coleus (Coleus forskholii Briq., Coleus aromaticus Benth. and Coleus zeylanicus Benth.). Plant extracts of C. forskholii exhibited high amounts of polyphenols and higher antioxidant activity in the tissues compared to C. aromaticus and C. zeylanicus. The leaf extracts of C. forskholii showed significantly high amounts of total polyphenols (23.46 mg g -1 fw), flavones and flavonols (250.8 µg g -1 fw) and high antioxidant activity (12.29 mM g -1 fw). HPLC profiling of leaf and stem tissues showed the presence of standard antioxidative polyphenols and more potent antioxidative polyphenols. Our results demonstrate that C. forskholii could be used as an important source of phenolic compounds with significantly high antioxidant activity.