Measurement of catechin-7-O -glucoside from barley to malt

Abstract

The content of catechin-7-O-glucoside throughout the malting process was evaluated by high-performance liquid chromatography with diode-array detection coupled to electrospray ionisation tandem mass spectrometry (HPLC-DAD-ESI/MS) in 10 Czech varieties of barley and corresponding malts. Glycosylation confers catechin better water solubility and resistance to oxidative and alkaline degradation, with a significant impact on beer quality. However, the sugar moiety also affects catechin bioavailability and may hinder its health effects. The results show that the total catechin-7-O-glucoside content is higher in malt [ranging from 22.3 ± 0.7 to 84 ± 6 mg catechin equivalents (CE)/kg] compared with barley (from 6.3 ± 0.4 to 36 ± 1 mg CE/kg). The catechin-7-O-glucoside content ratio between malt and barley varied from ~1.5- to 7-fold for varieties Pioner and Sunshine, respectively. The study of the glycosylation rate during individual stages of the malting process using a barley variety Tipple revealed that the content of catechin-7-O-glucoside gradually increases (0.26 mg CE/kg/h) during the germination stage (~3-fold higher after 120 h of germination). In addition, the glycosylation rate is 5 times faster during kilning steps (1.36 mg CE/kg/h) and its content almost doubles after kilning. The first steps of the kilning stage encompass optimal moisture and temperature for enzyme activity (~45% moisture and 55°C) which may explain the higher catechin-7-O-glucoside formation rate. © 2018 The Institute of Brewing & Distilling