Health Beneficial Effects and Chemical Profiles of Special Oolong Teas

Abstract

Background: Tea blended with medicinal plants usually consists of a mixture of active compounds that can increase the beneficial health effects. Eternity tea is dried tea leaves blended with ginger (Zingiber officinale), lemongrass (Cymbopogon citratus), and celery (Apium graveolens L.), and peaceful rest tea is dry tea leaves blended with Indian gooseberry (Phyllanthus emblica), Turkey berry (Solanum torvum Swartz), and wild betel leaf bush leaves (Piper sarmentosum Roxb.). These teas have been widely used for their ability to reduce blood sugar levels. However, there are no previous reports on their pharmacological activities. This work investigates the chemical profiles and pharmacological activities, especially the antidiabetes activity, of special oolong teas blended with local Thai medicinal plants (peaceful rest tea and eternity tea).Method: Eternity, Peaceful rest, and Oolong (Camellia sinensis) leaf samples were collected from Doi Chang organic tea plantation in Chiang Rai, Thailand. The chemical profiles of all tea samples were characterized by UHPLC-QTOF-MS. The extracts of these teas were investigated for their biological activities, including antioxidant, antiinflammatory, anticancer, and antidiabetic activities.Results: Catechins were found in eternity and oolong teas. Peaceful rest tea contained catechins/dimeric catechins, flavonoid glycosides, and alkaloids. Biological testing showed that peaceful rest and eternity tea extracts inhibited nitric oxide formation in a dose-dependent manner with IC50 values of 42.6 and 48.9 µg/mL, respectively. Peaceful rest tea extracts inhibited the growth of K562 human erythroleukemia cells. Furthermore, peaceful rest tea with both ethanol and water extracts demonstrated higher α-glucosidase inhibition activities than acarbose (IC50 = 75.71 µg/mL), with IC50 values of 10.6 and 1.22 µg/mL, respectively.Conclusions: Major antidiabetic compounds (5-O-Caffeoylquinic acid, kaempferol 3-O-glucosylrutinoside, and procyanidin B2) were found in peaceful rest tea. This finding corroborates that peaceful rest tea has greater antidiabetic effects than other teas against glucose and lipid levels. In vivo and clinical studies are therefore recommended to provide implications for the potential anti-diabetic properties of special oolong teas.