Enantiospecific determination of the odour threshold concentrations of (R)- and (S)-linalool in water and beer

Hop-derived linalool can substantially impact beer aroma. However, during the processing and storage of beer, the (R)-linalool predominating in hops can undergo racemisation to the less potent (S)-enantiomer. The aroma impact of the (S)-linalool was difficult to assess, because reliable threshold data were unavailable. To fill this gap, enantiopure (S)-linalool was isolated from the racemate by HPLC using a chiral column. This (S)-linalool was used in parallel to enantiopure (R)-linalool to determine enantiospecific odour threshold concentrations of linalool in water and unhopped beer with a trained sensory panel. Results revealed orthonasal odour detection threshold concentrations of 0.82 and 8.3 µg/kg in water and 6.5 and 53 µg/kg in beer, for (R)- and (S)-linalool, respectively. The higher odour potency of the (R)-linalool was thus confirmed, however, its odour threshold concentrations were found to be only 8 to 10 times lower than the odour threshold concentrations of the (S)-linalool and not 80 times as previously approximated from GC-O data. The data will help to better understand the aroma impact of (R)- and (S)-linalool in beer.