Extraction, analysis, and study on the volatiles in roselle tea

The Likens-Nickerson steam distillation procedure was utilized to mimic the preparation of roselle tea. Thermally generated volatiles from roselle were collected and analyzed by GC and GC-MS. There were four differently treated samples: untreated, frozen, hot-air-dried at 50 degrees C, and hot-air-dried at 75 degrees C. More than 37 compounds were characterized. They were classified into four groups: fatty acid derivatives, sugar derivatives, phenolic derivatives, and terpenes. Large amounts of the aliphatic C-6 lipid derivative, which contributes to the green note aromas, were in the fresh roselle, while only trace amounts were found in the frozen and air-dried samples. In the air-dried roselles, significant amounts of furfural and 5-methyl-2-furfural were formed, while only minimal amounts were detected in the fresh samples. There were no obvious changes in phenolic derivatives (eugenol) among the four samples. Terpenoid and oxide could also be isolated after distillation extraction. The drying process reduced them dramatically, especially the amount of alpha-terpineol, linalool oxide, and limonene. Principal component analysis (PCA) confirmed that characteristic roselle tea aromas depend upon a subtle quantitative balance of various components. A combination of the terpene derivatives with fragrance notes and the sugar derivatives with a caramel-like odor are responsible for the roselle aroma.