The Formation and Hydrolysis of Barley Malt Gel-Protein Under Different Mashing Conditions
S. Pöyri, 1, 4 M. Mikola, 2, 3 T. Sontag-Strohm, 2 A. Kaukovirta-Norja, 1 and S. Home 1
1 VTT Biotechnology, PO Box 1500, FIN-02044 VTT, Finland
2 University of Helsinki, Department of Food Technology, PO Box 27, FIN-00014 University of Helsinki, Finland
3 Current address, AVENA oy, Kansakoulunkatu 1 B, FIN-00100 Helsinki, Finland
4 Corresponding author. E-mail: saara.poyri@vtt.fi
J. Inst. Brew. 108(2), 261-267, 2002 | VIEW ARTICLE
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.
Key words:
Gel-protein, hordein, hydrolysis, mashing, oxidation, proteolysis.
Publication no. G-2002-0612-03R ©2002 The Institute & Guild of Brewing