Barley and Malt Proteins and Proteinases: III. A Simple Method for Estimating the Combined Actions of Malt Proteinases and the Extent of Protein Degradation during Malting

Abstract

The activities of barley and malt proteinases have been measured using haemoglobin and the highly degradable barley protein fraction (HDBPF) in malting and feed barley varieties. In conjunction, the barley and malt total protein and its components: hordein, glutelin, soluble proteins and free amino nitrogen (FAN) as well as Kolbach index were investigated. The comparative analysis of results revealed that the general grain modification index of Kolbach (KI), which was higher in malting varieties, was much more strongly associated with the levels of hordein degraded during malting than any other parameter investigated. The KI levels were also correlated with the increase in the levels of FAN, but not with the increase in the levels of soluble protein or changes in the glutelin component. The changes in total proteinase activity were low and cannot account for the increase in KI or the degraded hordein. The levels of total proteinase activity in both feed and malting barley varieties were similar. The results suggest that estimation of the levels of degraded hordein, during malting, is a sensitive indicator of the total proteolytic action of proteinases as well as the degradability of the reserve proteins. Therefore, we recommend measuring the amounts of hordein degraded during malting for the assessment of the impacts of grain protein and proteinases on malting barley quality of different varieties, in addition to KI and FAN.