Effects of infusion conditions on in vitro antioxidant power of extracts obtained from nutraceutical tea products developed with Osbeckia octandra and black tea leaves

Abstract

The present study was aimed at developing herbal tea bags using Osbeckia octandra leaves as the major ingredient and evaluating the effect of infusion conditions on their in-vitro antioxidant power of biologically active compounds extracted from the herbal tea bags. Five different tea bags (T1-T5) were prepared by incorporating dried O. octandra (leaves), Camellia sinensis (leaves), Zingiber officinale (rhizomes) and Allium sativum (bulbs) in different proportions. Each tea bag was infused at a constant infusion temperature of 100 ⁰C for 3, 5 and 7 minutes and for a constant infusion time of 7 minutes at different temperatures; 100, 90 and 80 ⁰C. Total phenolic (TP), total flavonoid (TF) contents, in vitro antioxidant activity by radical scavenging activity and ferric reducing antioxidant power of infused tea extracts were determined using spectroscopic methods. Results revealed that all extracts were rich with phytochemicals of phenolic compounds, flavonoids, tannins, terpenes, triterpenoids, phytosterols, saponins, alkaloids, amino acids and carbohydrates. Among the tea bags formulated, T1 which contains O. octandra leaves as the major ingredient (87%) showed significantly high values of in vitro ferric reducing antioxidant power compared to that of other tea bags tested at both infusion conditions. The infusion temperature of 80 ⁰C and time of 7 minutes as optimized infusion conditions showed the highest values of in vitro antioxidant activities for formulated tea bag containing O. octandra leaves (T1). Measures evaluated in this study were significantly different at both infusion conditions (p<0.05) for all the tea bags developed. Furthermore, the addition of O. octandra leaves to the black tea significantly improved TP and TF contents of tea products (p<0.05). Infusion temperature of 100 ⁰C and time of 3 minutes showed as the effective condition for extracting bioactive compounds from formulated black tea bags. Therefore, O. octandra incorporated to black tea have high content of bioactive compounds and should be shortly brewed with boiling water while tea bags containing only O. octandra should be brewed long at lower temperature.