Grape and Wine Proteins of White Wine Varietals

Abstract

To study the effect on stability of the various protein fractions present in wines a technique for purification and fractionation of the proteins was developed. This involved dialysis, gel filtration, and gel electrophoresis.

Fermentation and heat had somewhat similar effects but had different mechanisms in that they generally resulted in a decrease in protein content, a decided shift in the amount of protein in the various fractions, and occasionally the appearance of entirely new fractions. Fermentation had one effect not noted in the heat treatment: an occasional increase in total protein content as determined by the Diemair and Maier procedure. This increase is due to peptides released by the yeast during fermentation.

One interesting result was the finding that the yeast contributed no soluble heatunstable proteins to the wine.

Ion-exchange chromatography on DEAE-cellulose produced four fractions, one of which was stable to heat. Therefore, determination of total protein as a measure of protein stability of a wine is valueless since the individual proteins behave differently in their sensitivity to heat denaturation.