Use of ultrafiltration and proteolytic enzymes as alternative approaches for protein stabilisation of white wine

Abstract

Background and Aims: Precipitation of unstable proteins present in white wine after bottling can cause cloudiness, which is generally considered commercially unacceptable. Winemakers therefore use bentonite to remove protein prior to bottling, however, this can result in losses of wine volume and/or sensory quality. As such, there is interest in alternate strategies for protein stabilisation. This study evaluated the potential for ultrafiltration (UF), in combination with heat and proteolytic enzymes, to remove haze-forming proteins and stabilise white wine. Methods and Results: Heat-unstable white wines were fractionated using UF membranes with nominal 10 or 20 kDa molecular mass cutoff specifications, to first assess protein removal. Fractionation of wines with the 10 kDa membrane generated heat-stable permeate and protein-rich retentate. Pilot and semi-commercial scale trials were therefore conducted with 10 kDa molecular mass cutoff membranes and conditions optimised for heat and enzyme treatment of retentate. Heating retentate at 62°C for 10 min (with or without enzyme addition) achieved significant protein removal (30–96%, depending on the protein concentration of wine). Recombination of treated retentate with permeate gave wine that was almost heat-stable, such that a substantially reduced amount of bentonite (~50–60%) was required to achieve full heat stabilisation. Conclusions: Ultrafiltration can fractionate white wine, enabling targeted heat and enzyme treatment of a protein-rich fraction of wine, thereby mitigating the impacts of traditional stabilisation treatments on wine aroma and flavour. Significance of the Study: This is the first study to evaluate the combined use of UF, heat and proteolytic enzyme treatments as an alternative approach to protein stabilisation of white wine.