Characterization of aroma and aroma-active compounds of roselle (Hibiscus sabdariffa L.) teas obtained by three different infusions

In this study, the effects of two different traditional brewing methods used frequently in Benin (TI1 (40 minutes/100°C) and TI2 (24 hours/ ambient temperature)) and an alternative brewing method suggested by Ramirez-Rodrigues et al. (2011) (IR (16 minutes/ 98 °C)) on aroma, aroma-active compounds, total phenolic content and antioxidant activity of Hibiscus sabdariffa tea were investigated. Liquid-liquid extraction method was used to determine the aroma of the samples. The aroma-active compounds were investigated by GC-MS-Olfactometry technique by applying Aroma Extract Dilution Analysis (AEDA). A total of 38, 39 and 38 aroma compounds were identified by GC-MS in TI1, TI2 and IR, respectively. The highest amount of aroma compounds was found in TI2 sample (176545 µg/kg). Furans were the most dominant volatiles in Hibiscus sabdariffa teas with the lead of furfural in general. Furfural was identified as the most dominant aroma-active compound (FD=2048-4096) responsible for caramel, bready odors in all samples. Another aroma-active compounds detected in roselle infusions with high intensities were 5-methyl-2-furfural (caramel), acetic acid (vinegary), 3-penten-2-ol (oily, herbal), nonanal (herbal, grassy), benzaldehyde (almond), eugenol (spicy) and 3-methyl-3-buten-2-one (fruity). The FD factors of these Hibiscus sabdariffa aroma-active compounds were relatively higher in TI2. Sensory evaluation revealed that TI2 is more preferred by panellists and displayed higher intensities of aroma, fruity, sweet and caramel attributes than TI1 and IR. This is in agreement with results from the olfactometric analysis. The total phenolic contents of TI1, TI2 and IR determined by Folin-Ciocalteu method were 714, 358 and 761 mg/kg gallic acid equivalents, respectively. Antioxidant activity of TI1, TI2 and IR investigated with DPPH assay were 714, 358 and 761 mM/kg Ttrolox equivalents respectively. This study has shown that sample preparation methods can significantly affect the total phenolic compounds, antioxidant activities, aroma and aroma-active profiles of Hibiscus sabdariffa. When compared to the tea samples, TI2 (24 hours/ ambient temperature) tea was determined to be richer in aroma and aroma-active compounds and this infusion had greater sensory acceptability than other teas (TI1 and IR).