Thermal Stability of Thaumatin-Like Protein, Chitinase, and Invertase Isolated from Sauvignon blanc and Semillon Juice and Their Role in Haze Formation in Wine

A thermal unfolding study of thaumatin-like protein, chitinase, and invertase isolated from Vitis vinifera Sauvignon blanc and Semillon juice was undertaken. Differential scanning calorimetry demonstrated that chitinase was a major player in heat-induced haze in unfined wines as it had a low melt temperature, and aggregation was observed. The kinetics of chitinase F1 (Sauvignon blanc) unfolding was studied using circular dichroism spectrometry. Chitinase unfolding conforms to Arrhenius behavior having an activation energy of 320 kJ/mol. This enabled a predictive model for protein stability to be generated, predicting a half-life of 9 years at 15 °C, 4.7 days at 30 °C, and 17 min at 45 °C. Circular dichroism studies indicate that chitinase unfolding follows three steps: an initial irreversible step from the native to an unfolded conformation, a reversible step between a collapsed and an unfolded non-native conformation, followed by irreversible aggregation associated with visible haze formation.