Characterization of natural haze protein in sauvignon white wine

The natural precipitate of a white Sauvignon wine was dissolved, lyophilized and analyzed by molecular exclusion FPLC and/or electrophoresis (SDS–PAGE, native and isoelectrofocusing) using three types of stains (Coomassie blue, silver stain and PAS stain). The protein spots were digested and analyzed by MALDI-TOF/TOF MS. Direct analysis of the precipitates by SDS–PAGE gave no bands with Coomassie blue stain and five bands with silver stain. It was not possible to identify these bands by MALDI-TOF/TOF MS. However, applying molecular exclusion FPLC prior to SDS–PAGE improved sensitivity and enabled three bands to be identified. These were the previously described thaumatin-like protein (VVTL1) and two proteins that to our knowledge have never been described as components of protein haze: β-(1-3)-glucanase and ripening-related protein grip22 precursor.