The role of ferulic acid and arabinoxylan in inducing premature yeast flocculation

Premature yeast flocculation (PYF) is a universal phenomenon and has caused serious problems in the brewing industry. For brewing quality control, it is of great value to investigate the PYF factors that induce this destructive phenomenon. In the present study, two barley malts (PYF+ and PYF-), made from the same barley cultivar by one maltster in China, were selected for PYF factor investigations. The results showed that considerably higher amounts of the bound ferulic acid (FA), rather than arabinoxylan (AX), existed in the PYF+ wort compared with the PYF- wort. To better understand the role of these polysaccharides in PYF+ and PYF- wort, they were fractional precipitated with graded ethanol concentrations. The AX and FA contents in each fraction, as well as the molecular weight profiles and monosaccharide composition, were determined. Furthermore, the PYF-inducing activities of each fraction were measured using a small-scale fermentation. It was found that the 40% ethanol-precipitated fraction of both the PYF+ and PYF- wort, and the 60% fraction from the PYF+ wort, could induce the severe PYF phenomenon when added to the PYF- wort. These fractions were proposed to contain PYF factors of suitable molecular weight and a sufficient amount of the polysaccharides. In addition, it was found that the bound FA in arabinoxylan behaved as an important PYF factor in barley malt. The results of this work may contribute to the further study of the PYF mechanism. Copyright (c) 2015 The Institute of Brewing & Distilling