Profiling of Hop-Derived Flavan-3-ols from Lager Beer in Relation to Hopping Technology

Abstract

Little is understood regarding the fate of polyphenols during beer aging. Lager beers were produced with varying hopping regimes to investigate hop product contribution to beer polyphenol and flavanol contents. Finished beers underwent forced aging (30°C) and were monitored for changes in flavan-3-ol profiles. Sephadex LH20 resin was used to produce polyphenol-rich isolates from the finished and aged beers. European Brewery Convention standard spectrophotometric methods and reversed-phase HPLC coupled with diode array detection and electrospray ionization mass spectrometry (RP-HPLC-DAD-ESI(–)-MS) were used to measure polyphenol and total flavanoid contents of the lager beers and the polyphenolic-rich isolates. Phloroglucinolysis was used in conjunction with RP-HPLC-ESI(–)-MS to reveal flavan-3-ol subunit composition and to estimate changes in proanthocyanidin relative mean degree of polymerization. The beers produced with varying hopping regimes were different in total polyphenols and flavonoids by spectrophotometery. Six major phloroglucinolysis flavan-3-ol products were observed; however, galloylated flavanols were not detected in any of the beers. The predominant subunits by molar ratio were (+)-catechin followed by (–)-epigallocatechin, except for beers brewed solely with spent hops, which were also high in (–)-epicatechin by molar ratio. The major extension subunit was (+)-catechin for all treatments. Total flavanoid and proanthocyanidin contents of the beers increased initially during storage, with eventual decreases occurring after 6 weeks of storage.