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Haze can appear in white wines as a result of the denaturation and subsequent aggregation of grape pathogenesis-related (PR) proteins. Yeast cell-wall polysaccharides, particularly mannoproteins, represent a promising strategy to reduce the incidence of this phenomenon. The aim of this study was to evaluate the effects of 13 Starmerella bacillaris strains, in sequential fermentation with Saccharomyces cerevisiae, on wine protein stability of three white wines (Sauvignon blanc, Pinot grigio, and Manzoni bianco). The resulting wines were characterized in terms of their chemical composition, content of PR proteins and polysaccharides, and heat stability. In addition, the mannoprotein fraction was purified from six wines, five produced with S. bacillaris and one with S. cerevisiae EC1118 used as control. Generally, wines produced with S. bacillaris strains were more heat-stable, despite generally containing higher amounts of PR proteins. The increased heat stability of Starmerella wines was attributed to the stabilizing effect resulting from their higher concentrations of both total polysaccharides and mannoprotein fractions. In particular, for the most heat unstable wine (Manzoni bianco), the low MW mannoprotein fraction resulted to be the most involved in wine stability. The ability to produce wines with different heat stability was demonstrated to be strain-dependent and was more evident in the most unstable wines. By reducing fining waste, the use of S. bacillaris as an enological starter can be proposed as a new tool to manage wine protein stability for a more sustainable winemaking.

International audience; Bentonite fining is the most popular treatment used to remove proteins in white and rose wines. The usual heat test used to adjust the bentonite dose consists of heating the wine during 30 min at 80 degrees C. At this temperature, all of the proteins are unfolded, and this can lead to an overestimation of the dose. We have shown that proteins adsorb on bentonite in a specific order and, more importantly, that the proteins responsible for haze formation adsorb first. Fluorescence spectroscopy showed that this is due to the structural properties of proteins, which can be classified as hard and soft proteins. Alternative heat tests were performed at a lower temperature (40 degrees C) and showed a better correlation with accelerated aging. These tests were also less dependent upon the wine pH.

The presence of protein in white wines represents a major problem for the wine industry mainly due to the fact that proteins generate haze in the bottled white wines. Protein instability, which results in wine haze formation, is due to some grape PR-Proteins that thanks to their intrinsic resistance survive the vinification process, pass into the wine where cause the appearance of undesirable haze and deposits, leading to rejection by consumers. Protein hazing of white wines is considered to be a three-step process, involving protein denaturation followed by aggregation into colloidal particles able to scatter the visible light and make the wine turbid. Because of the complexity and the variability of the wine matrix, the factors and mechanisms involved in this process are still largely unknown. Commonly, winemakers prevent haze formation by removing the proteins through the use of bentonite. However, this treatment causes loss of wine and, being unspecific, also the removal of some aroma compounds. It has been calculated that the total cost deriving from bentonite treatments corresponds to a worldwide total amount of 1 billion dollars per year. Therefore, basic and applied research is still needed to solve the problem of protein haze formation in white wines. Firstly, the present thesis faces the problem of the impairment of aroma due to bentonite fining. In particular, the study arises from a previous investigation which suggested the existence of an interaction between proteins and aroma compounds. In this context, the interaction of the main wine protein VVTL1 with some fatty acid ethyl esters (FAEE), which are important fermentative aroma compounds has been investigated. Due to the difficulty to determine this interaction at the molecular level, Synchrotron Radiation Circular Dichroism (SRCD) has been used to study the secondary structure of the wine protein as affected by the interactions with FAEE having different chain lengths. Subsequently, the research continued with the investigation of the role played by tannins in the phenomena leading to protein instability of white wines. To this purpose, the effects of several polyphenols (deriving from wine and not) on the stability of VVTL1 has been investigated using SRCD. In parallel, the capability of tannins to react with the proteins over time in bottled wine has been evaluated by Dynamic Light Scattering (DLS) studies in a model wine system. In addition, the thermal stability of two purified proteins, which are representative of the major classes of proteins in white wine (i.e. a class IV Chitinase and the VVTL1), has been investigated by Differential Scanning Calorimetry (DSC) in the presence of the tannins purified from wine at different times after bottling. Finally, the last part of the research focuses on the possibility to produce good quantities of grape proteins in pure form starting from the in vitro culture of berry pulp tissues. These proteins can be used for molecular and functional characterisation. In particular, with this technique it is possible to label the proteins by cultivating the cellular tissues in the presence of N15 which allows the study of their fine structure and interactions by spectroscopic methods.

Proteins determine several key sensory and technological properties of beer. Most of the protein components of beer are barley pathogenesis–related proteins, which endure the harsh brewing treatments. Due to their intrinsic resistance, they can also survive gastrointestinal digestion in humans, evoking immune responses in predisposed individuals. For these reasons, beer proteins have been studied for several decades. However, only the recent development of the mass spectrometry–based proteomic techniques is disclosing the “deep” proteome of beer. Several dozens of barley- and yeast-derived proteins constitute the current “core” proteome of beer, while many others are specific to beer brands or styles. Proteolytic peptides of beer include a multitude of sequences derived from prolamins that are potentially harmful for celiacs. In this chapter, we survey the compositional and functional aspects of the beer proteome/peptidome emphasizing the most recent findings obtained using the newest proteomic approaches.

The wine trade is one of the most relevant voices in the food sector. To date, the attention paid by modern consumers towards food quality has raised interest in defining quality markers for wine and in preventing wine fraud. Proteins are minor components of both white and red wines, with little nutritional relevance, but they have an impressive impact on its quality and safety. The present chapter exhaustively summarizes the state of the art of wine proteomics, including several very recent reports on the study of contaminating proteins in wines. The issues include (1) the reliable quantification of total proteins in white and red wines, (2) the methods applied to wine protein characterization, (3) the investigation of wine protein origin, (4) the role of specific wine proteins in haze formation, (5) the link between some wine proteins and foam formation and stability in sparkling wines, and (6) the use of wine proteomics as a tool for traceability.

Protein haze development in white wines is an unacceptable visual defect attributed to slow protein unfolding and aggregation. It is favored by wine exposure to excessive temperatures but can also develop in properly stored wines. In this study, the combined impact of pH (2.5-4.0), ionic strength (0.02-0.15 M), and temperature (25, 40, and 70 °C) on wine protein stability was investigated. The results showed three classes of proteins with low conformational stability involved in aggregation at room temperature: β-glucanases, chitinases, and some thaumatin-like protein isoforms (22-24 kDa). Unexpectedly, at 25 °C, maximum instability was observed at the lower pH, far from the protein isoelectric point. Increasing temperatures led to a shift of the maximum haze at higher pH. These different behaviors could be explained by the opposite impact of pH on intramolecular (conformational stability) and intermolecular (colloidal stability) electrostatic interactions. The present results highlight that wine pH and ionic strength play a determinant part in aggregation mechanisms, aggregate characteristics, and final haze.