Comparative studies on chemical stability, antioxidant and antimicrobial activity from hot and cold hibiscus (Hibiscus sabdariffa L.) calyces tea infusions

Hibiscus calyx presents high content of bioactive compounds, such as anthocyanins and other phenolic compounds responsible for antioxidant activity. The present study investigated how the tea infusion temperature (hot and cold) can change the phytochemical profile, antimicrobial activity, and stability of hibiscus tea. The results indicated the same phytochemical profile for cold (infusion during 2 h/25 °C) and hot (7 min/75 °C) tea by using FTIR and UPLC-MS/MS analyses. Hibiscus tea, hot or cold, showed antimicrobial activity against strains of Salmonella Typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus, with minimum inhibitory concentration (MIC), obtaining values between 62.5 and 125.0 mg/ml. The hot infusion was more efficient for the bioactive compounds extraction, being 47% higher for total anthocyanins. After 48 h at 5 °C, the anthocyanin content had an average decrease of 30% (cold tea) and 48% (hot tea). Tea cream content increased to 15% (cold tea) and 37% (hot tea) after 72 h storage. Regarding the color, it was observed that after 48 h storage there was a clearing of the teas, and the L* coordinate increased from 21.03 to 24.93, and 20.72 to 24.90 for cold and hot tea, respectively. Our study indicates that hibiscus tea provides more antioxidants when prepared in the hot condition (7 min at 75 °C), and soon after cooled to 5 °C. Finally, it is recommended that hibiscus tea be consumed up to 24 h from preparation even when kept refrigerated.