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WINE

make the wine stable. Therefore, it is necessary to fine the wine by adding proteins that interact with substances that are responsible for instability and cause their precipitation (Marchal et al., 2002). In this paper, the wine fining ability of corn zeins was studied. These proteins are particularly rich in glutamic acid (21-26%), leucine (20%), proline (10%) and alanine (10%) (Shukla and Cheryan, 2001). The high proportion of non-polar amino acids makes zeins relatively hydrophobic (Kojima et al., 1997) and this property could determine the effectiveness of these plant proteins in fining red wine, as previously shown for animal gelatin (SarniManchado et al., 1999). The data here reported indicate that only the zeins prepared in the presence of a reducing agent were effective in fining wine. Native zeins occur as a heterogeneous protein mixture that also contains disulfide-linked aggregates. Under reducing conditions, the disulfidebonds in the aggregates are broken which induces the release of protein monomers with molecular weights of 17 kDa (corresponding to β-zein), 22 (α-zein) and 27 kDa (γ-zein) (ESEN, 1987). Since wine fining ability of proteins seems to depend mainly on their molecular weight and conformation (Maury et al., 2003), the good fining effectiveness of RZ could be due to the presence of proteins with a relatively low molecular weight (<32 kDa), which could be obtained by treating corn flour with a reducing agent. In contrast, the low fining ability of the native zein (non-reduced) may be due to the inaccessibility of the phenol-binding sites, which

are buried inside the disulfide bond-stabilized protein structure. Therefore, the reduction of disulfide bonds by opening the protein structure would improve the binding site accessibility by favoring polyphenol-protein interactions through hydrophobic interaction and hydrogen bonds. The best results in reducing turbidity were obtained with 10 g/ hL of RZ; the turbidity values were similar to those measured in the wine treated with G1 at the same concentration. The decrease in anthocyanin concentration after RZ treatment was also similar to that observed with G1. These results were also confirmed for zeins, indicating that their behavior is similar to that of other protein fining agents (Sarni-Manchado et al., 1999). The hue and color of RZ-treated wine was unaffected by the fining treatment as was previously observed using other plant proteins (Lefebvre et al., 1999). In summary, corn zeins extracted under reducing conditions show a good fining action in term of decreasing turbidity, removing phenolic compounds and preserving red wine color. The clarifying ability of zeins is similar to that of animal gelatin so this plant protein could be a good substitute for animal proteins in winemaking. To complete this study, more compositional and sensory analyses are needed to evaluate what impact the use of RZ as fining agent has on wine aroma. Due to the chemical-physical properties of corn zeins they have many industrial applications such as in the production of fiber, adhesives, coatings, ceramics, inks, cosmetics, textiles, chewing gum and degradable

24 - Italian Food & Beverage Technology - LX (2010) march

plastics (Shukla and Cheryan, 2001). The use of corn zeins as a wine-fining agent could be another application for these proteins. In the present study, RZ was extracted from the residue remaining after the water/salt-soluble components were removed from maize flour. The direct extraction of zeins from a commercial corn gluten sample gave exactly the same SDS-PAGE protein pattern as the zeins extracted from maize flour. Therefore corn gluten, the residual by-product produced in very large quantities by the corn processing (starch) industry, could probably be used to produce a low-cost fining agent that could be successfully employed in wine making. Finally, zeins are designated as “Generally Recognized As Safe” (GRAS) by the American Federal Drug Administration and, unlike wheat gluten, are safe for consumers suffering from celiac disease. The risk for allergic patients is also rather low, since allergies to corn seem to be rarer than those to other protein materials of plant and animal origin that are used or have been proposed for use as wine-fining agents (Mills and Breiteneder, 2005). From “Italian Journal of Food Science” nr. 1/2009

REFERENCES AOAC. 1984. “Official Methods of Analysis”, 14th ed. Association of Official Analytical Chemists. Arlington. VA. Boulton R., Singleton V., Bisson L. and Kunkee R. 1996. “Principles and Practices of Winemaking”. Chapman & Hall, New York. Cao N.G., Xu Q., Ni J. and Chen L.F. 1996. Enzymatic hydrolysis of corn starch after

ITALIAN BEVERAGE TECHNOLOGY 60/2010  

Rivista esclusivamente in inglese, sviluppata a supporto di tutte quelle aziende italiane che vogliono puntare sull’export di macchine, prod...

ITALIAN BEVERAGE TECHNOLOGY 60/2010  

Rivista esclusivamente in inglese, sviluppata a supporto di tutte quelle aziende italiane che vogliono puntare sull’export di macchine, prod...