Modulating role of SO2 in white wine protein haze formation
Abstract
Despite the extensive research performed during the last decades, the multifactorial mechanism responsible for the white wine protein haze formation is not fully characterized. Herein, a new model is proposed, which is based on the experimental identification of sulfur dioxide as a major modulating factor inducing wine protein haze upon heating. As opposed to other reducing agents, such as 2-mercaptoethanol, dithiothreitol and tris(2-carboxyethyl)phosphine hydrochloride (TCEP), the addition of SO2 to must/wine upon heating cleaves intraprotein disulfide bonds, hinders thiol-disulfide exchange during protein interactions and can lead to the formation of novel inter/intraprotein disulfide bonds. Those are eventually responsible for wine protein aggregation which follows a nucleation-growth kinetic model as shown by dynamic light scattering [1]. Protein aggregates were further studied following heat stress to induce aggregation. We were able to dissolve the aggregates in buffer A (8 M urea, 200 mM NaCl and 30 mM sodium citrate pH 3) and B (4 % SDS, 200 mM NaCl and sodium citrate pH 3). Size-exclusion chromatography (SEC) of the dissolved proteins aggregates allowed the characterization of the different species present in solution under reducing and non-reducing conditions. Determination of free sulfhydryl groups present in native and stressed protein was also performed using 5,5ʹ-dithiobis(2-nitrobenzoic acid) (DTNB). We suggest/demonstrate that protein aggregation due to SO2 modulation under wine model solution occurs as a result of the combination between both hydrophobic interactions and the formation of new interprotein disulfide bonds. DTNB assay revealed that there were no free sulfhydryl groups both in native, heat stressed and heat stressed in the presence of SO2. Future work will focus on the study of the different protein aggregate species and on new methods for wine protein stabilization.
[1] Chagas, R., Ferreira, L. M., Laia, C. A., Monteiro, S. & Ferreira, R. B. (2016). The challenging SO2-mediated chemical build-up of protein aggregates in wines. Food Chemistry, 192, 460-469.
Issue: Macrowine 2016
Type: Poster
Authors
*FCT/UNL