Protein in wine

Hsu, J. C. and Heatherbell, D. A. (1987). Heat-unstable proteins in wine. I. Characterization and removal by bentonite fining and heat treatment. Am. J. Enol. Vitic. 38,11-16. 

Kwon, S. W., Profiling of soluble proteins in wine by nano-high-performance liquid chromatography/ tandem mass spectrometry. Journal of Agricultural and Food Chemistry 52(24), 7258-7263, 2004. 

Cheynier, V. et al., The structures of tannins in grapes and wines and their interactions with proteins. In Wine. Nutritional and Therapeutic Benefits (ed. T.R. Watkins), American Chemical Society, Washington, DC, 1997, p. 81. 

Kwon, S.W. (2004). Profiling of soluble proteins in wine by nano-high-performance liquid chro-matography/tandem mass spectrometry. J. Agric. Food Chem., 52, 7258 - 7263 Lee, T. (1986). Protein instability nature, characterization and removal by bentonite Leiper, K.A., Stewart, G.G., McKeown, I.P., Nock, T, Thompson, M.J. (2005). Optimising beer stabilisation by the selective removal of tannoids and sensitive proteins. J. 1. Brewing, 111, 118-127... 

Since the proteins in wine are very low (normally lower than lOOmg/L), concentration of the sample is performed prior to analysis. Moreover, it is also useful to reduce the content of interfering substances such as salts, acids and polyphenols. This can be done, either before or after the protein concentration, by dialysis with low cut-off membranes. 

Figure 7.12 Nano-LC/MS analysis of a peptide from a protein in wine (a) total ion current (TIC) chromatogram of the tryptic digest (MW range 60-75 kDa in SDS-PAGE). (b) Full MS spectrum at retention time 13.08min (m/z 400-1500). (c) The MS/MS spectrum of m/z 603.9 identified the peptide SSEAVDDVDQR. (Reproduced from J. Agric. Food Chem., 2004, 52(24), 7258-7263, Kwon, with permission from the American Chemical Society)...

Rodriguez-Delgado, M.A., Malovana, S., Montelongo, F.J. and Cifuentes, A. (2002) Fast analysis of proteins in wines by capillary gel electrophoresis, Eur. Food Res. Technol., 241, 536-540. 

A method of sample preparation proposed for MS/MS analysis of proteins in wine is by enzymatic hydrolysis of gel pieces from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using trypsin (Kwon, 2004). Hydrolysis occurs at the carboxyl side of lysine and arginine residues. Protocols of protein precipitation, enzymatic digestion, and sample preparation are reported in Table 10.5. 

Ribereau-Gayon demonstrated in 1932 that it was possible to adsorb unstable proteins in wine using kaolin, a negatively charged clay. However, large quantities of kaolin, on the order of 500 g/hl, are necessary to obtain protein stability. This makes kaolin treatment impracticable dne to the volnme of lees it produces and the amonnt of wine lost. 

Fig. 10.3. Diagram of the flocculation mechanism of proteins in wine dnring fining (Riberean-Gayon et al, 1977)...

Isoelectric points for proteins in wine are between 3.6 and 7.1 (Zoecklin, 2000). In some years, wine pH is at or above 3.6. For those proteins above their isoelectric points, they become negatively charged and Bentonite has no effect. In that case, it becomes much more difficult to clarify the wine. 

---