Characterisation and Assessment of the Role of Barley Malt Endoproteases During Malting and Mashing 1
A. M. Osman, 2 S. M. Coverdale, 2 N. Cole, 3 S. E. Hamilton, 4
J. de Jersey, 4 and P. A. Inkerman 2
1 Parts of the data reported in this paper were presented at 48th Australian Cereal Chemistry Conference, Cairns, 1998, and 9th Australian Barley Technical Symposium, Melbourne, 1999.
2 Barley Quality Laboratory, Farming Systems Institute, Toowoomba, 4350, Australia.
3 Barrett Burston Malting Co.Pty.Ltd., GPO Box 153B, Melbourne, 3001, Australia.
4 Department of Biochemistry, The University of Queensland, St Lucia, 4072, Australia. Corresponding author. E-mail: Abdalla.Osman@dpi.qld.gov.au
J. Inst. Brew. 108(1):62-67, 2002 | VIEW ARTICLE
ABSTRACT
Barley malt endoproteases (EC.3.4.21) develop as multiple isoforms mainly during grain germination and pass through kilning almost intact. Thermostability, under simulated mashing conditions, varied from low to high depending on the substrate used in the assay. This suggests that individual enzymes respond differently to heat exposure and to protein substrates. The optimal pH with haemoglobin was pH 3.5, with hordein pH 4 and with glutelin pH 5. The optimal temperature with hordein was 40oC, with glutelin 50oC and with haemoglobin 60oC. These differences suggest that it is not possible to comprehensively characterise all malt endoproteases under one set of assay conditions. In brewing, most of the barley protein degradation (> 70 %) occurs during malting. But some proteinases remain active during mashing and contribute to wort soluble proteins and free amino nitrogen. Their contribution to all malt EBC mash total free amino nitrogen was 25 % in Schooner (Australian) and 30 % in Morex (USA). The importance of proteolytic activity during mashing and the possibility that the levels may not be adequate, at high solid adjunct ratios, are acknowledged.
Key words:
Barley, endoprotease, malt, mash, thermostability.
Publication no. G-2002-0320-01R ©2002 The Institute & Guild of Brewing