Monitoring of Glycosidically Bound Polyphenols in Hops and Hop Products Using LC-MS/MS Technique

Abstract

Recent findings have shown that besides bitter acids, several additional hop ingredients contribute to beer bitterness. These belong to the class of polyphenols and are also part of the hard resin fraction of hops. They include the two well-known flavonols, quercetin and kaempferol, widespread in the plant kingdom. On the other hand, the so-called multifidols are more typical to hops as intermediates in the biosynthesis of alpha- and beta-acids. Both of the above mentioned flavonols and the multifidols occur mainly not in their free forms but rather bonded to sugars such as glucose. In our study, the contents of such glycosidically bound polyphenols were determined in a worldwide spectrum of different hop varieties using liquid chromatography in combination with tandem mass spectrometry. In total, more than 500 samples from crops 2020 and 2019, representing 34 different varieties, were analyzed. The detected concentrations (mg/100 g) were dependent on variety, with ranges between of 6–155 for co-multifidol glucoside, 3–60 for ad-multifidol glucoside, 13–87 for quercetin-3-O-glucoside, 5–46 for quercetin-3-O-rutinoside, and 4–35 for kaempferol-3-O-glucoside. Moreover, their fate during large scale hop extraction was investigated. It was confirmed that polyphenol glycosides were not extracted with supercritical carbon dioxide but were extracted with ethanol.

Keywords:

• Hard resins
• hop polyphenols
• multifidols
• quercetin, kaempferol

Disclosure statement

No potential conflict of interest is reported by the authors.