Hops (Humulus lupulus L.) are essential
raw materials
for beer brewing, and the major contributors to beer bitterness are
isohumulones (iso-α-acids) and humulinones. In recent years,
many breweries have focused on the production of hop-forward beer
styles by adding hops after or during the cold fermentation stage,
which will tend to release humulinones or other hop-derived bitter
compounds. In this study, a LC-MS/MS method was developed for quantification
of 60 hop-derived bitter compounds in 25 min. Reverse-phase chromatography
with an alkaline methanol/acetonitrile (70:30) mobile phase was used
for the separation. The quantitative range was 0.053–3912 ng/mL
with correlation coefficient r > 0.99, and the
LOQ
were 0.26 and 0.053 ng/mL for iso-α-acids and humulinones. Precision
(RSD < 5.0%) and accuracy (recovery 86.3%–118.1%) were both
satisfactory. The abundance of hop-derived bitter compounds in the
dry-hopped beer (Double-India Pale Ale) and the nondry-hopped beer
(Vienna Lager) were monitored throughout the fermentation and storage
stages, and the formation of oxidation and cyclization products showed
difference profiles between these two beers. The quantification results
reveal how hop-derived bitter compounds change throughout the brewing
process, as well as the influence of hops and brewing techniques on
beer bitterness.