Grape proteins

In addition to metabolic enzymes, other major proteins present in the mature grape berry are pathogenesis-related (PR) proteins, including chitinases (PR3 family) and thaumatin-like proteins (TLP, PR5 

---

Duncan, B. (1992). Varietal differences in white grape protein Implications for bentonite fining. Aus. New Zealand Wine Ind.. 7,189-193. 

R Gonzalez-Lara, LM Gonz ez. Hydrophobic interaction—HPLC analysis of soluble grape proteins. Int J Biochromatogr 1 309-314, 1996. 

In red wine, only one grape protein was found (thaumatin) all other proteins were from Saccharomyces cerevisiae and a few others from plant pathogens and fungi (e.g., Botryotinia fuckeliana, Sclerotinia sclerotiorum, and Aspergillus aculeatus) (31). 

White wines contain relatively large amounts of insoluble proteins that slowly precipitate from the solution (the initial protein precipitation begins during pressing). Most white wines are to deficient in phenolics, causing a quick and complete protein precipitation. Protein haze may be due to the fraction of residual wine proteins that have been rendered prone to precipitation by their interaction with reactive phenolics (from the grape, and also rarely from the cork). Bentonite removes different amounts of grape protein fractions (Moine-Ledoux and Dubourdieu 1999). 

The mechanism of protein haze formation in wines is not fully understood. Slow denaturation of wine proteins is thought to lead to protein aggregation, flocculation into a hazy suspension and, finally, formation of visual precipitates. The importance of non-proteinaceous factors in white wine protein haze formation such as proan-thocyanidins (Koch and Sajak 1959 Waters et al. 1995a Yokotsuka et al. 1991) have been suspected for some time. Other factors such as polysaccharides, alcohol levels and pH have also been implicated (Mesquita et al. 2001 Siebert et al. 1996a). It has been observed that grape protein added to model wine does not precipitate or produce haze when heated, whereas visually obvious hazes occur when the same protein is added to a commercial wine (Pocock 2006). 

Koch, J., Sajak, E. (1959). A review and some studies on grape protein. Am. J. Enol. Vitic., 10, 114-123... 

The method of sample preparation for grape proteins analysis should be chosen according to the aim of the study. If grape proteins have to be studied in relation to wine characteristics and technology, it is convenient to start from the so-called free run juice , a material representative of the must, in which the proteins are supposed to be involved in the winemaking process and wine quality. The free run juice is obtained by... 

CE on uncoated silica capillaries of grape proteins was used for varietal differentiation of Muscadine grapes, giving more than 20 well resolved peaks (Mazhar et al., 2002). 

Grape proteins have been separated on C18 (Santoro, 1995 Peng etal., 1997) and C8 (Tattersall et al., 1997) stationary phases. A widely used column is the Vydac C18 (Peng et al., 1997 Waters et al., 1998), which allows separation of different forms of grape thaumatin-like proteins (WTL) and chitinases (Chit) (Figure 7.8). 

Grape proteins can be analyzed by LC/MS and MALDI-TOF, ESI-MS analysis is used as a complement to DNA methods in the variety characterization. 

The resemblance between grape and PR proteins (chitinase and thaumatin) does not prove that they are identical molecules. In fact, none of the proteins in grapes have the extreme sweetening properties of thaumatin and thaumatin and chitinase antibodies do not react with grape proteins (Pigarra-Pereira et al, 1998). 

All white wines namrally contain grape proteins, which may canse tnrbidity and deposit if they lloccnlate (Section 5.5.2). There are tests for... 

---