How wort boiling process affects flavonoid polyphenols in beer
Keywords:polyphenols, flavonoids, flavonoid-O-glycosides, prenylflavonoids, wort boiling, hops, beer
Beer and brewing raw materials are a source of number of polyphenol substances with potential or proven beneficial biological effects. In pilot brews of Czech pale lager (200 l) the behavior of hop-derived polyphenol substances during wort boiling process in various hopping regimes was studied. Prenylflavonoids, flavonoids and their O-glycosides were determined by liquid chromatography coupled to high resolution mass spectrometry (LC-HR / MS) with sample preparation by the QuEChERS method. The concentration of flavanols (catechin, epicatechin) in hopped wort and beer is dominated by hop raw material, when hopping with aromatic hops rich in polyphenols, 2/3 of the amount in beer is affected by hops. In contrast, the concentration of their mono-O-glucosides in beer does not depend on hopping. Flavonols quercetin, kaempferol and multifidol are found in wort and beer mainly in glycosidic form. The source of all these substances in beer is exclusively hops. Conversely, malt is the only source of myricetin and myricetin-O-glucoside in beer. Main part of hop-derived flavonoids is released during wort boiling into wort within 15-30 minutes. Splitting the hop dose or low pressure boiling technology had no significant effect on health-promoting polyphenols. Beer hopped with hops rich in flavonoids contains a relatively high amount of health-promoting polyphenols, while beer hopped with hop extract is very poor in these antioxidants.