Investigation of haze-related proteins and phenolics in the pulp, skin and seed of Sauvignon Blanc grapes

Abstract

Grape proteins, in particular pathogenesis-related (PR) proteins, are responsible for wine protein haze formation. In addition, phenolic compounds extracted during grape processing have been identified that can participate in the appearance of hazes. This study investigated the distribution of proteins and phenolics in the pulp, skin and seed of Sauvignon Blanc grapes, especially those compounds involved in white wine protein hazes. Polyacrylamide gel electrophoresis (PAGE) analysis of protein extracts showed that proteins with molecular weights (MW) referring to thaumatin-like (TL) protein and chitinase were present in both skins and pulp. Quantification of TL protein and chitinase in different grape tissues were conducted using RP-HPLC by comparing the retention time of purified PR proteins. Concentrations of total phenolics and tannin were determined by Folin-Ciocalteau colorimetry and methylcellulose precipitation (MCP), respectively. The results showed that seeds contained the highest concentration of total phenolics and tannin. Remarkably, concentration of tannin in Sauvignon Blanc skins was comparable to the level reported in red grapes. No tannin was detected in the pulp. These results indicate that managing the extraction of juice from grape components during processing might reduce the bentonite requirement for stabilisation of the resultant wine.