Residual proteins in finished wines can aggregate to form haze. To obtain insights into the mechanism of protein haze formation, a reconstitution approach was used to study the heat-induced aggregation behavior of purified wine proteins. A chitinase, four thaumatin-like protein (TLP) isoforms, phenolics, and polysaccharides were isolated from a Chardonnay wine. The same wine was stripped of these compounds and used as a base to reconstitute each of the proteins alone or in combination with the isolated phenolics and/or polysaccharides. After a heating and cooling cycle (70 °C for 1 h and 25 °C for 15 h), the size and concentration of the aggregates formed were measured by scanning ion occlusion sensing (SIOS), a technique to detect and quantify nanoparticles. The chitinase was the protein most prone to aggregate and the one that formed the largest particles; phenolics and polysaccharides did not have a significant impact on its aggregation behavior. TLP isoforms varied in susceptibility to haze formation and in interactions with polysaccharides and phenolics. The work establishes SIOS as a useful method for studying wine haze.

The wine aroma loss as a consequence of treatments with bentonite is due to the occurrence of multiple interaction mechanisms. In addition to a direct effect of bentonite, the removal of aroma compounds bound to protein components adsorbed by the clay has been hypothesized but never demonstrated. We studied the effect of bentonite addition on total wine aroma compounds (extracted from Moscato wine) in a model solution in the absence and presence of total and purified (thaumatin-like proteins and chitinase) wine proteins. The results showed that in general bentonite alone has a low effect on the loss of terpenes but removed ethyl esters and fatty acids. The presence of wine proteins in the solution treated with bentonite tended to increase the loss of esters with the longest carbon chains (from ethyl octanoate to ethyl decanoate), and this was significant when the purified proteins were used. The results here reported suggest that hydrophobicity can be one of the driving forces involved in the interaction of aromas with both bentonite and proteins.

Background and Aims There is a growing interest in finding alternative wine fining agents to replace potentially allergenic animal‐derived and plant‐derived proteins. In this context, the potential use of grape‐derived fining agents would be beneficial as they would not introduce additional, potentially allergenic products to the finished wine. In this project, grape seed flour, a by‐product of the grape oil seed industry, has been used to prepare a grape seed extract (GSE) for testing as a novel wine fining agent. Methods and Results The fining performance of GSE was compared with that of patatin, pea proteins, polyvinylpolypyrrolidone and potassium caseinate in a white and in a rosé wine, and of ovalbumin and gelatin in a red wine. Reduction of turbidity, effect on wine colour, the concentration of phenolic substances, browning potential and wine sensory attributes were determined. Grape seed extract was effective in decreasing white wine turbidity when compared to potassium caseinate. In red wine, GSE removed some anthocyanin and proanthocyanins, while wine colour was only slightly affected. The greatest GSE effect was observed on the sensory properties of the treated wines, as it strongly reduced the vegetal notes in the rosé wine and improved the overall taste of the red wine as a result of the reduction in both acidity and astringency. Conclusions Grape seed extract can be considered a valid allergen‐free alternative to the most common wine fining agents. Significance of the Study Grape seed extract is the first effective fining agent endogenous to grapes, thus not attracting the legal restrictions concerning the presence of foreign substances.

Protein-fining agents from animal and plant sources are used to clarify and stabilise wines and lower their astringency. Health concerns have been raised because most of the proteins used for wine fining are derived from allergenic sources. To overcome this problem, this study proposed the use of a grape seed protein extract as a new fining agent for wine. The procedure is described for extract preparation from grape seed flour, the by-product of the grape oil seed industry. Four extracts of grape seed protein were prepared using glycine and sodium carbonate buffers at two concentrations (0.05 and 0.2 M, pH 10.5). The capacity of the extracts for removing potentially astringent phenols from tannin solutions and from red wines was assessed by determining the Astringency Mucin Index. The perceived astringency intensity in tannin solutions and in two red wines treated with the extracts was evaluated by sensory tests. The Astringency Mucin Index and astringency intensity of treated samples were significantly lowered compared to that of untreated samples. Grape seed extracts appear a promising tool for wine fining as a substitute for exogenous proteins

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