Harvesting and processing sauvignon blanc effects on the protein content of juice and protein stability of wine

Abstract

The concentrations of proteins and phenolics in juices and wines from hand harvested and mechanically harvested Sauvignon Blanc grapes were determined under different grape processing conditions for two consecutive vintages (2011 and 2012). Haze-forming pathogenesis-related (PR) proteins, specifically thaumatin-like proteins (TLPs) and chitinases, were identified and quantified by RP-HPLC. Juices and wines from mechanically harvested grapes showed lower protein levels than from hand harvested grapes under the same grape processing conditions; the same result was observed for phenolics in juice samples, but no significant difference was detected in phenolic content of wines. More protein and phenolic contents were extracted from grapes into juice of the 0-1.6 MPa pressing than those of the 0-0.4 MPa and 0-0.8 MPa pressings. The protein concentration of wines made from the 0-0.4 MPa pressing tended to be lower than for the other two pressings. The concentration of PR proteins showed similar trends amongst treatments as total proteins. In addition, the bentonite requirements of wines showed a very good linear correlation with the concentration of chitinases. The results suggested that heavier grape pressing gives rise to greater PR protein extraction from grapes into juice. Lower protein content, particularly PR proteins, in resultant juices and wines from mechanically harvested grapes may require less bentonite for protein stabilization. Comparing to TLPs, the removal of chitinases is more important to reduce the dosage of bentonite.