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Comparative antioxidant capacity of Jiaogulan (Gynostemma pentaphyllum) water and methanol extracts measured by various tests

An estimated 60-80% of the world’s population relies on medicinal plants for treatment of numerous ailments and almost 65% of world’s population has incorporated traditional medicine into primary modality of health care (Farnsworth et al., 1985). Many indigenous medicinal plants have been found useful for successful management of diabetes. One of them is Jiaogulan (Gynostemma pentaphyllum) – a plant that grows wild in China, as well as many other countries throughout Asia. In China, it has been consumed for many years as an energizing tea in the local communities. Scientific research studies in China have shown that Jiaogulan decreases cholesterol by improving the liver's ability to send sugar and carbohydrates to the muscles for conversion to energy instead of turning the sugar into triglycerides which the body stores as fat. It improves fat metabolism, reduces blood triglyceride levels and decreases the accumulation of lipid peroxide and fat sediments in the blood vessels. Biologically active compounds from Jianogulan preparations show positive effects in the treatment of diabetes, hepatitis B and bronchitis. In our study we determined the antioxidant capacity and quantified various classes of phenolic antioxidants in aqueous infusions and methanol extracts of Jiaogulan tea from two different producers. We used three spectrophotometric methods (Ferric Reducing/Antioxidant Power assay (FRAP), 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay, and 2, 2´-azinobis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) assay), as well as cyclic voltammetry and oxygen radical absorbance capacity (ORAC) to determine the antioxidant potency of Jaogulan aqueous and methanol extracts. We also quantified various classes of phenolic compounds in these preparations: total phenols (Folin–Ciocalteu assay), total flavonoids (colorimetric assay with Al2Cl3) and free phenolic acid content (UPLC-MS/MS) with an assumption that these compounds are largely responsible for protective effects of Jiaogulan preparations. Total phenol content, total flavonoid content and antioxidant capacity were slightly diferrent in water and methanol extracts of Jiaogulan from two different producers. Methanol extraction resulted in higher contents of polyphenolic compounds as well in antioxidant capacity measured by different tests. Eight free phenolic acids were detected in both, methanol and water extracts. The most abundant free phenolic acid in tea produced by Cedar Biote Sdn Bhd (Malezia) was chlorogenic acid (253.86±24.35 µmol/g dw in methanol and 218.31±33.78 µmol/g dw in water exstracts). In tea purchered from Sanleaf Europe GmbH (Germany) the most abudant free phenolic acid was 4-coumaric acid (409.4±33.78 µmol/g dw in methanol and 354.56±54.21 µmol/g dw in water extract). Our results suggest that G. pentaphyllum water and methanol extracts have high antioxidant capacity and significant content of polyphenolic compounds such as chlorogenic acid which contribute to the prevention of Type 2 Diabetes Mellitus and cardiovascular disease.

antioxidant capacity; G. pentaphyllum; phenolic compounds

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