THE USE OF HORDEIN FRACTIONS TO ESTIMATE PROTEOLYTIC ACTIVITY IN BARLEY AND MALT

Abstract

When the natural barley protein, hordein, is used as a substrate for the assay of exopeptidase and endopeptidase activity in green malts, the enzymic activities found differ significantly from those obtained using non-barley substrates such as dipeptides, gelatin or haemoglobin. Malts having similar total levels of carboxypeptidases as measured using non-barley substrates showed considerable variation in the extent to which these enzymes break down barley hordein. Malts also varied more in their endopeptidase activity with hordein than in their ability to digest gelatin or haemoglobin. Analyses of hordein by gel chromatography and gel electrophoresis indicate that it consists of eight main components, which can be divided into three groups of proteins, with molecular weights in the regions of 15,000, 65,000 and ≥ 100,000. Barley samples differed in their relative contents of these proteins and this variation could be rapidly assessed using gel electrophoresis.