The objectives of this study were to 1) measure and compare the compositional differences of essential oil among three hop cultivars ('Centennial’, 'Citra' and 'Nelson Sauvin'), 2) identify the odor-active aroma compounds in three varieties of hops and 3) investigate the behavior of hop-derived aroma compounds in beers prepared by dry-hopping approach with three hop varieties.
The major compositions of essential oil of three hop varieties ('Centennial', 'Citra' and 'Nelson Sauvin') were determined. Myrcene, β-caryophyllene and α-humulene were dominant compositions in all cultivars while certain esters as well as linalool and geraniol were relatively abundant in 'Centennial' and 'Citra' hops. The odor-active compounds in these three hop varieties were identified using gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and aroma extract dilution analysis (AEDA). Application of AEDA revealed myrcene (celery, balsamic notes), isovaleric acid (smelly,rancid and cheese notes) and geraniol (citrus note) as the most important aroma components in all hop cultivars by presenting the highest flavor dilution (FD) factors, followed by S-methyl methanethiosulfonate (radish, cabbage notes), linalool (floral, sweet notes) and vanillin (vanilla note). S-methyl methanethiosulfonate, having unique radish, cabbage notes, was detected in the hops for the first time and showed high FD factors in 'Centennial' and 'Citra' hops. Several sulfur-containing compounds were also identified as important contributors to hop aroma. Dry-hopped beer with 'Centennial', 'Citra' and 'Nelson Sauvin' revealed an increase of myrcene and α-humulene whereas the increase of β-caryophyllene was only in 'Citra' variety. Linalool and geraniol increased significantly in hopped beer. Due to the importance of linalool and aroma contribution differences of stereoisomers, the chiral isomers in both hops and beers were further studied. The results demonstrated the prevalence of R-linalool in hops and a conversion of R-linalool to S-linalool in beer was observed in control beer when hops were added at beginning of wort boiling.