Determination of benzoxazinoids in wheat and rye beers by HPLC-DAD and UPLC-QTOF MS

Abstract

Phenolic compounds in beer have received considerable interest. Besides the more typical phenolic acids and flavonoids, beer contains also lesser-known compounds, such as hordatines, their agmatine precursors and other phenolamines. Current work shows that beers brewed from wheat or rye malts, in addition to barley malts, contain benzoxazinoids, a group of nitrogen containing secondary metabolites typical to wheat and rye. In this work, HPLC-DAD was used for the quantification of major benzoxazinoids in 32 wheat and four rye beers. Of the wheat beers 22 samples and all of the rye beers contained benzoxazinoids, or their breakdown products. Concentrations of DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one) (as aglycon) varied from 1.7 to 21.9mg/l in wheat beers and from 5.6 to 31.6mg/l in rye beers. Breakdown products BOA (benzoxazolin-2-one), found in 15 beers, and MBOA (6-methoxy-benzoxazolin-2-one), found in two beers, were measured at concentrations ranging from 2.4 to 10.7mg/l and 8.4 to 10.5mg/l, respectively.Identification of benzoxazinoids by UPLC-QTOF MS was done on selected beers. Benzoxazinoid profiles varied greatly between different wheat beers, and compared to rye beers the chemical diversity of benzoxazinoids was higher. As far as the authors know, this is the first time that other benzoxazinoids, rather than just the decomposition products BOA or MBOA, have been reported in beer. The results also show that benzoxazinoids can be present in beer glycosylated with three or four hexose units.