The Formation and Hydrolysis of Barley Malt Gel-Protein Under Different Mashing Conditions

Abstract

The effect of oxidation and proteolysis on the amount of gel-protein aggregate was investigated both in vivo during mashing and in vitro. The oxidation of the free thiol groups of proteins to disulphide bridges during mashing appeared to be a good indicator of the formation of gel-protein aggregate. The pH optimum of the oxidation varied according to the isothermal mashing temperature. The results suggested that the oxidation of the thiol groups maybe a result of some kind of enzymatic activity. In vitro experiments showed that the proteolysis of the gel-protein aggregate was strongest at pH 5.0 and temperature denaturation occurred only at temperatures over 80°C. Mashing experiments on the other hand suggested that the proteolysis of the monomer subunits of gel-protein (i.e. B- and D-hordein) had a stronger effect on the final amount of the gel-protein aggregate than the hydrolysis of the aggregate.