Low-molecular-weight materials from heavily roasted barley and malt with strong foam-stabilising potential

Abstract

Extracts of roasted barley and black malt made both at room temperature and using a ramped temperature mashing regime contained relatively low concentrations of protein. However cold water extracts displayed strong foaming power even at very low measurable protein concentrations. The observation that very little material appeared to be precipitated out by ammonium sulphate based salt fractionation is consistent with the very low protein levels and it is inferred that the powerful foaming potential is not due to polypeptides. The foaming material in black malt was investigated in some detail. It was purified under conditions that indicated that it is of molecular weight <4000 and is relatively anionic. A solitary foam-active fraction was recovered using preparative HPLC and time of flight mass spectrometry revealed one large peak and two small peaks. The larger peak is tentatively identified as pyridyl pyrazine, while we believe that the smaller peaks are due to peptides, which we tentatively identify as a hexa- and a tetrapeptide. The Fourier transform infrared spectrum is consistent with pyridine, pyrazine and peptide being components of this foaming entity. © 2018 The Institute of Brewing & Distilling