β-Glucan is a polymer of glucose, which is joined together by roughly 30 % β-1,3- and 70 % β-1,4 glycosidic bonds. The majority of these polymers (approx. 75 %) are formed in the cell walls of the barley endosperm (the rest consists of proteins and pentosans). A partial depolymerization of the β-glucans takes place during malting through the action of β-glucanases. Further degradation during mashing is limited by the temperature sensitivity of the β-glucanases. For this reason, poorly modified malt may contain high molecular weight β-glucans (> 10,000 Da), potentially leading to difficulties during the processes of lautering and filtration.
Enzymatic determination of high-molecular weight β-glucan ([(1-3) (1-4)]-β-D-glucan)
wort, beer
High molecular weight β-glucans contained in wort and beer are precipitated with ammonium sulfate and washed with 50 % ethanol by volume. Samples are suspended in a buffer solution with a pH of 6.5, hydrated, and then incubated with purified lichenase enzyme and filtered. Lichenase cleaves these polysaccharides specifically, primarily forming trisaccharides and tetrasaccharides. An aliquot of the filtrate is then completely hydrolyzed with purified β-glucosidase. Additionally, a small portion of higher molecular weight oligosaccharides is created. These oligosaccharides are quantitatively cleaved to form glucose molecules. The amount of glucose is determined with a glucose oxidase/peroxidase mixture.