Wine proteins levels

Effect of Growing and Harvesting Conditions on Subsequent Wine Protein Levels. .. 216... 

Unfortunately, in spite of the published literature on wine proteins, we do not know the actual protein levels at which table or dessert wines are stable. The changes in protein content during production and processing of wines are still not known with sufficient accuracy to predict their behavior. The winemaker has to depend on empirical tests if he is to produce protein stable wines. Early separation of new wines from their fermentation yeast greatly improves their chances for protein stability by decreasing the release of yeast autolysis products into the wine. 

Despite the vast literature on protein instability, the actual protein levels at which wines will remain protein-stable are unknown. Wine proteins are a mixture of probably more than 100 proteins derived from the grape, yeast (Dambrouck et al. 2003), autolyzed yeast (Charpentier et al. 1986) and sometimes Botrytis cinerea when grape berries are not sound (Cilindre et al. 2007). Variety, vintage, maturity of the fruit, pH, and processing methodology affect both the must and the wine protein contents. Yeast proteins, however, have not been shown to play a role in white wine... 

Casein is nearly insoluble and must be dissolved at pH 11. Potassium caseinate is water-soluble and is preferred for this reason. Sodium caseinate is usually not used because it increases the sodium content of wine. Casein is a positively charged protein that flocculates in acidic media such as wine. When added to wine, casein adsorbs and mechanically removes suspended materials as it settles. In general, casein is used to remove undesirable odors, to bleach color and to clarify white wines. It is sometimes used as a substitute for carbon in color modification of juice and white wine. Usage levels are typically 10-30 g/hL. 

Protein levels in white wine have been reported by several authors and have been shown to differ by variety. Lee (1986) reported a range of protein concentration from 18 to 81 mg/L in 14 wines from different Australian regions and made from different varieties. Some of these wines appeared to have been fined with bentonite prior to analysis. Pocock et al. (1998) reported concentrations in unfined Australian wines up to several hundred mg/L. Hsu and Heatherbell (1987b) found a range of 19 4 mg/L in four different unfined white wines from Oregon, while a very large variation (20—260 mg/L) was noted by Bayly and Berg (1967). 

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). 

Extraction. Since the protein level in wine is normally < lOOmg/L, and interfering substances (e.g., salts, acids, and polyphenols)... 

White wines were uniformly low in HA protein, while red wines were quite variable (Siebert et al., 1996b). Vitis vinifera white wines had very low levels of HA polyphenols, while Vitis labrusca white wines had higher and vinifera-labrusca hybrids had intermediate levels (Siebert et al., 1996b). All red wines had high levels of HA polyphenols, and most had low levels of HA protein the two exceptions were both hybrids. 

A sensory study based on an incomplete factorial design allowed to demonstrate that astringency of procyanidins was reduced in the presence of rhamnogalaturonan II added at levels encountered in wine but was modified neither by anthocyanins nor by the other wine polysaccharides (mannoproteins and arabinogalactan proteins). Increase in ethanol level resulted in higher bitterness perception but had no effect on astringency. 

Iron and copper in wines may form complexes with other components to produce deposits or clouds in white wines. Iron clouds generally occur at a pH range from 2.9 to 3.6 and are often controlled by adding citric acid to the wines (2). Copper clouds appear in wines when high levels of copper and sulfur dioxide exist and are a combination of sediments, protein-tannin, copper-protein, and copper-sulfur complexes (169). Further, the browning rate of white wines increases in the presence of copper and iron (143). The results of this study indicate that iron increased the browning rate more than copper. 

Even when no additive is used in winemaking, the necessity for small-lot trial before production scale operation is apparent. Because a high percentage of wine is consumed only after chilling, and because chilling may accelerate the precipitation of potassium acid tartrate, ill-defined colloids, anthocyanin-tannin polymers, proteins, etc., simple cold stabilization by refrigeration in the winery may irreversibly alter the product and its eventually-perceived quality level. It often happens, especially in heavy-bodied red varietal wines, that a dark, amorphous precipitate may form in the bottle over several years. Usually tannoid,... 

The main part of the works relating to the determination of BAs in wines concern the major ones, such as His and Tyr few studies have been performed on amines such as Spd and Spm. These amines, even though they appear less toxic than His and Tyr (115,116), nevertheless exert many functions at the cellular level. For instance, by their polycationic long-chain structure they can interact with DNA, RNA, proteins, and the membrane phospholipides (117,118), and they are also strongly implied in cellular growth phenomena. The presence of these polyamines in grapes and the role that they play have been studied for some years (119). 

Girbau, T., Stummer, B. E., Pocock, K. F., Baldock, G. A., Scott, E. S., and Waters, E. J. (2004). The effect of Uncinula necator (powdery mildew) and Botrytis cinerea infection of grapes on the levels of haze-forming pathogenesis-related proteins in grape juice and wine. Aust. J. Grape Wine Res. 10,125-133. 

Wine is one of the most complex and interesting matrices for a number of reasons. It is composed of volatile compounds, some of them responsible for the odor, and nonvolatile compounds which cause taste sensations, such as sweetness (sugars), sourness (organic acids), bitterness (polyphenols), and saltiness (mineral substances Rapp and Mandary, 1986). With a few exceptions, those compounds need to be present in levels of 1%, or even more, to influence taste. Generally, the volatile components can be perceived in much lower concentrations, since our organs are extremely sensitive to certain aroma substances (Rapp et ah, 1986). Carbohydrates (monosaccharides, disaccharides, and polysaccharides), peptides, proteins, vitamins, and mineral substances are among the other wine constituents. 

If, after the laboratory tests, a wine is judged to be protein-unstable, a laboratory fining series is run, adding different levels of bentonite to the wine. The series is tested for protein instability with one of the tests previously mentioned, and the level of bentonite needed to prevent haze occurring under the test conditions is selected for use in the cellar. 

Karadjova and coworkers [90] in a detailed and comprehensive investigation established a scheme for fractionation of wine components and Cu, Fe, and Zn determination in the different fractions. Like Fe, the other two metals may analogously exist in wines as free ions, as complexes with organic acids and as complexes with proteins, polyphenols and polysaccharides. The resin XAD-8 was used for the separation of wine polyphenols. Dowex ion exchange resins were used for the separation of cationic and anionic species of metals that were subsequently quantified off-line in Bulgarian and Macedonian wines by FAAS or ET-AAS (depending on their concentration levels). 

Sulfate is one of the Hofmeister series of anions, a ranking of the ability of various ions to precipitate proteins (Kunz et al. 2004). In simple terms, precipitation of proteins by kosmotropic anions occurs due to salting out - a competition between the anion and the protein for water of solvation resulting in a loss of water from the protein surface. This process is classically applied in ammonium sulfate precipitation as the first step in many protein purification schemes, although the levels employed are several fold higher than those in wine. In the particular case of white wine, this loss of water of solvation, even by a relatively low amount of sulfate anion, by a protein in a solution containing a variety of cations and other anions and... 

Pocock, K.E, Hayasaka, Y, McCarthy, M.G., Waters, E.J. (2000). Thaumatin-like proteins and chitinases, the haze-forming proteins of wine, accumulate during ripening of grape (Vitis vinifera) berries and drought stress does not affect the final levels per berry at maturity. J. Agric. Food Ghent., 48, 1637-1643... 

Partitioning of volatile substances between the liquid and gas phases is mainly governed by aroma compound volatility and solubility. These physicochemical properties are expected to be influenced by wine constituents present in the medium, for instance polysaccharides, polyphenols, proteins among others. Consideration of the physicochemical interactions that occur between aroma compounds and wine constituents is necessary to understand the perception of wine aroma during consumption. The binding that occurs at a molecular level reflects changes at a macroscopic level of the thermodynamic equilibrium, such as volatility and solubility, or changes in kinetic phenomena. Thus, thermodynamic and dynamic approaches can be used to study the behaviour of aroma compounds in simple (model) or complex (foods) media. 

Among wine polysaccharides, mannoproteins play an important role in protein haze stabilisation (Waters et al. 1994 Dupin et al. 2000). Gelatin fining of a wine phenolic extract in wine-like solution resulted in a much higher precipitation rate than when the same treatment was applied on the original wine. After addition of wine polysaccharides at the concentration normally encountered in wines, precipitation was reduced back to the level measured in wine, confirming the stabilizing effect of polysaccharides (Cheynier et al. 2006). 

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