Herbal tea from processed leaves of <i>Justicia secunda</i> (blood leaves): Effects of drying temperature and brew conditions on total soluble solids, phenolic contents, and antioxidant capacity

Justicia secunda (blood leaves) is a medicinal plant used widely in Nigeria for its diverse physiological functions, especially blood-boosting, antimalarial, antioxidant, anti-hypertension, and anti-diabetes. Fresh leaves of J. secunda are used in rural communities in Nigeria to prepare herbal teas by infusion and boiling. In this study, green and black herbal teas were prepared by infusion and boiling of the processed leaves of J. secunda. The influence of brew conditions (infusion, boiling, liquid-solid ratio, and brew time) on the total soluble solids (TSS) was investigated and used as a baseline to determine the total polyphenols content (TPC), flavonoid content, and antioxidant capacity of the herbal teas. Brew conditions (2 g/250 mL, 20 min) produced green and black tea extracts with relatively high TSS content (0.43-0.64 g). The black tea contained high polyphenols [28.29 mg gallic acid equivalent (GAE)/g] and flavonoids [72.75 mg quercetin equivalent (QE)/g] than the green tea under similar brew conditions (2 g/250 mL; boiled or infused) which correlated with the ferrous reducing power and metal chelating antioxidant activities of the extracts. The cold macerated leaf extract contained slightly higher amounts of flavonoids (75.25 mg QE/g) which also exhibited good antioxidant capacity. Thus, the infusion method of brewing is recommended over boiling since it produces more beneficial ingredients than the fresh leaves extract. The results also suggest a convenient procedure of drying, along with brewing, which can be easily used at the household level or on a commercial scale to produce high-quality J. secunda tea.