Abstract
The present study compared the performance of two colorimetric protein assays, the Bradford and the potassium dodecyl sulphate/bicinchoninic acid (KDS/BCA) methods, for use in wine and grape juice analysis. The Bradford assay was strongly affected by protein type, whereas the KDS/BCA method had lower protein-to-protein variation, with BSA and lysozyme revealing a response slope similar to that of wine proteins. In the Bradford assay, the presence of 12% ethanol and 200 mg/l of wine polyphenols lowered the protein response by 28 and 16%, respectively, whereas in the KDS/BCA assay, the interference was insignificant. Among 64 white wines, the correlation between protein haze potential as determined by a heat test and protein content was better for the KDS/BCA assay. This study confirms the superiority of the KDS/BCA assay over the Bradford assay for quantifying protein in white grape juice and wine, and provides better predictive value with respect to the risk of white wine protein instability.
- ©2014 by the American Society for Enology and Viticulture
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