Elucidation of key odorants in Beninese Roselle (Hibiscus sabdariffa L.) infusions prepared by hot and cold brewing.

Roselle (Hibiscus sabdariffa L.) is an edible flower belonging to the large family of Malvaceae. Aroma is one of the crucial parameters to determine the final tea overall quality and the consumer's preference and it is affected by different processing factors (drying, heating, brewing etc.). The aim of this study was to compare hot and cold brewing procedures on the aroma and aroma-active compounds of Beninese Roselle for the first time. Three different infusions were prepared and coded as R16M (16 min/98 °C), R40M (40 min/98 °C) and R24H (24 h/at ambient temperature). The aroma compounds of the infusion samples were extracted by liquid liquid extraction (LLE) method and determined by gas chromatography-mass spectrometry (GC-MS). A total of 38, 38 and 39 aroma compounds including alcohols, furans, acids, ketones, aldehydes, volatile phenols, lactones, pyranone, pyrrole, terpene and ester were detected in R16M, R40M and R24H infusions, respectively. The total aroma concentration of the cold infusion sample (R24H) was higher than those of two hot infusions. A significant reduction was found in the amount of these compounds in the sample prepared by hot infusion with 16 min (R16M). In all three samples, furans were identified as the dominant aroma group followed by alcohols. Based on the results of the aroma extract dilution analysis (AEDA), a total of 22 and 23 different key odorants were detected in hot infusions (R16M and R40M) and cold infusion (R24H) (ambient temperature), respectively. The powerful key odorants with regard to FD (flavor dilution) factors in all samples were prevailingly furans, alcohols, and aldehydes. The highest FD factors were found in furfural and 5-methyl-2-furfural providing caramel and bready notes. Principal component analysis (PCA) showed that Roselle infusions could clearly be discriminated in terms of their aroma profiles. The findings of this study demonstrate that the brewing procedures have a important impact on the final aroma and key odorants of Roselle infusions.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.