Some phenolic compounds in Czech hops and beer of Pilsner type

The HPLC method coupled with eight-channel coulometric detector (CoulArray) was used for determination of polyphenolic compounds in Pilsner beer and hops cultivated in the Czech Republic. Some important flavonoids and isoflavonoids as well as some phenolic acids were analysed. The CoulArray detector is characterized by its high sensitivity and enables determination in very low concentration. Calibration ranged from 0,001 mg/L to 1 mg/L of each analytes without any clean‑up procedure before analysis. The two HPLC gradients with different content of acetonitrile as an organic modifier were used. Specific oxidative potencial of each phenolic compound enables higher degree of selectivity of these chromatographic methods..

Compounds with higher polarity, like phenolic acids (gallic, protocatechuic, gentisic, 4-hydroxyphenylacetic, vanillic, caffeic, syringic, and ferulic acid) besides flavan-3-ols (catechin and epicatechin), 4-hydroxycoumarin and derivatives of coumarin (esculin, umbelliferone, scopoletin) could be separated completely with 30 % content of acetonitrile in mobile phase only. 4-hydroxycoumarin, flavonoids or their glycosides (rutin, naringin, myricetin, quercetin, apigenin) and some isoflavonoids (daidzein, genistein, formononetin and biochanin A) had to be eluated with a higher content (50 %) of acetonitrile in the mobile phase due to their higher hydrophobicity. The typical representative compounds from wide spectrum of phenolics were chosen for establishing of composition of Czech hops and beer of Pilsner type.

BrewingScience - Monatsschrift für Brauwissenschaft, 61 (January/February) 2007, pp. 32-37