beta-Glucosidase removal due to bentonite fining during wine making

摘要

Grape proteins are discussed to cause haze formation in bottled wine leading to economic problems. A common way to remove these proteins is bentonite fining. Although the efficiency of bentonite treatment is well known, the underlying molecular mechanism of the fining process in wine is not well understood. Two white wine varieties, Riesling and Pinot gris, were treated in the must stage with different types of bentonite to investigate their efficiencies. In all cases, bentonite treatment significantly reduced the overall protein concentration based on SDS-PAGE analysis, albeit individual proteins were differently affected. However, our data indicate that one protein band was completely removed independent of the bentonite type. Mass spectrometry analysis identified the major protein as glucan endo-1,3-beta-glucosidase of Vitis vinifera, which was accompanied by low amounts of several other proteins. Using molecular modeling, we propose that this enzyme with its positively charged surface is adsorbed on the negatively charged lamella of bentonite during the fining process.