Effect of Wine Composition on Protein Stability

¹ Instituto Superior de Agronomia, Universidade Técnica de Lisboa, 1349-017 Lisboa, Portugal
² Instituto Superior de Agronomia, Universidade Técnica de Lisboa, 1349-017 Lisboa, PortugalEscola Superior Agrária de Castelo Branco, 6001 Castelo Branco Codex, Portugal
³ Instituto Superior de Agronomia, Universidade Técnica de Lisboa, 1349-017 Lisboa, PortugalInstituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2781-901 Oeiras, Portugal

ferreira{at}itqb.unl.pt

Six Portuguese varietal wines (Fernão Pires, Assario, Tamarez, Verdelho, Arinto, and Moscatel) were used to study the factors that control protein insolubility in wines stored at high temperatures. Each wine exhibited a characteristic pattern of turbidity formation when exposed to increasing temperatures (30 to 80 °C). This pattern of turbidity formation, highly specific for each wine, also varied in wines prepared from the same grape variety from different vintages. This pattern was not determined by the proteins. When wine A was depleted of its own protein and back-added with the protein from wine B, it behaved like wine A. It was concluded that the nonprotein components or characteristics of each wine determine the typical pattern of haze formation when the wine is incubated at elevated temperatures. Protein concentration in a given wine correlated positively with the intensity of turbidity formation at any given temperature. Addition of a protein of nonwine origin (bovine serum albumin) to a protein-free wine did not alter the typical pattern of haze formation of the wine. Added ethanol did not change the pattern of haze formation at high temperatures. Wine polysaccharides did affect the characteristic behavior, increasing protein instability under moderately high temperatures (40 to 50 °C). In addition, the wine proteins were increasingly heat-stable when the pH of the solution in which the proteins were dissolved increased from wine pH to 7.5. Thus, the pattern of protein instability with increasing temperature that is typical of each wine is not determined by the proteins. It seems to be controlled and determined by a combination of nonprotein factors, such as the presence of polysaccharides and the wine pH.

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Acknowledgment: This work was financially supported by the Fundação para a Ciência e a Tecnologia, under project no. PRAXIS XXI/3/3.2/AGR/2180/95.

Key words: Protein stability, wine composition, Portuguese wines