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Am. J. Enol. Vitic. 45:3:319-326 (1994)
Copyright © 1994 by the American Society for Enology and Viticulture.
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Protein Instability of Wines: Influence of Protein Isolelectric Point

H. Dawes 1, S. Boyes 1, J. Keene 1, and D. Heatherbell 2

1 The Horticulture and Food Research Institute of New Zealand, Private Bag 92 169, Auckland, New Zealand.
2 Lincoln University, P. O. Box 84 Lincoln University, Canterbury, New Zealand.

Proteins in Gewürztraminer wine were separated by an improved method of chromatofocusing using an FPLC system in conjunction with characterization by isoelectric focusing. Bentonite fining resulted in removal of all the different protein fractions. There was no bentonite selectivity based on isoelectric point (pl). The amount of protein depletion correlated approximately linearly with the level of bentonite addition. Five groups of proteins of differing pl were assigned after characterization of 35 individual FPLC fractionated proteins by isoelectric focusing. The five groups of proteins were added back separately to protein-free wine. Unfractionated protein was similarly added to fined protein but not phenolic-free wine and to tartrate buffer (pH 3.14). All additions of protein were at a concentration of approximately 75 mg/L, a level at which considerable haze was visible after heating bentonite fined wine. All protein groups were thermally unstable contributing to haze/sediment formation. Marked differences in the precipitation/coagulation of the protein groups after a heat/cold test were observed. The high pl (ge 7.0) protein groups developed a compact sediment; the middle pl (predominately 5.94 to 5.36 and 5.36 to 4.65) groups a flocculated precipitate 4 to 5 times larger than that of the high pl groups, and the low pl (< 4.65) group a suspended haze. The two samples containing all pl proteins also developed compact sediments. The interaction of proteins with other components in wine, primarily phenolics, must be considered in order to determine factors resulting in instability of wine.

Key words: Gewürztraminer, protein isoelectric point, heat stability, Coomassie blue assay, protein instability

Submitted on April 20, 1993




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B. C. Trela
Protein Stabilization in a Model Wine Solution with Phytic Acid
Am. J. Enol. Vitic., September 1, 2008; 59(3): 312 - 316.
[Abstract] [Full Text] [PDF]


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Copyright © 1994 by the American Society for Enology and Viticulture.