A Review and Some Studies on Grape Protein

¹ Institut fur Obstund Gemüseverwertung der Hessischen Lehrund Forschungsanstalt fur Wein-, Obstund Gartenbau in Geisenheim/Rheingau.

The investigation, still incomplete, indicates that wine protein is of rather complex structure. The Voit-N, when multiplied by 6.25, can be used to calculate the "crude protein" of wine but not the "wine protein." It is very probable that the Voit precipitate includes the "soluble" grape proteins, which may be identical to its water-insoluble fraction.

The water-soluble constituents are suspected to be low-molecular-weight polypeptides and proteids. The proteins consist of different nitrogen bodies (globulins) that can be separated electrophoretically. So far, 17 amino acids have been identified with certainty as building blocks of these nitrogen bodies. If is not yet known how 5 of these are distributed among the electrophoretically separated fractions. Nor is it known in what order they are connected and how many peptide chains we are dealing with. Also unknown is the temperature coefficient for wine protein denaturation. In practice, heat treatment of wines and must leads quickly to protein stability, while bentonite treatment results in a protein-free wine.