There Arabic gum is obtained from the exudate of two varieties of acacia of African origin, l'Acacia Senegal and theAcacia Seyal. Chemically, gum arabic is a hydrophilic colloid made up of a mixture of oligosaccharides of arabinogalactans, and glycoproteins. The ratios between the sugars that form the polysaccharide and glycoprotein chains are different in the arabic gums obtained from Acacia Seyal e Acacia Senegal.
In addition, more glucuronic acid is contained in Seyal gum arabic than in Senegal gum arabic.
Like the more stable wine polysaccharides, arabic gums can be classified as globular substituted or branched protein arabinogalactans (AGPs).
In food field gum arabic is used as a gelling agent, emulsifier, stabilizer, glazing agent and agglutinator.
It is called a stabilizing agent a substance that is capable of give viscous solutions that improve the consistency, the body and the precipitation stability of solutions or emulsions.
The simultaneous presence of hydrophilic carbohydrates and hydrophobic proteins allows gum arabic to perform the stabilizing function of protective colloid, exploited in the wine sector.
Like all hydrophilic colloids, gum arabic, added to wine, is able to modify its viscosity characteristics and consequently to have an exponential influence on its fluidity (and on all technological processes such as filtration that are linked to it). Compared to linear structure polysaccharides (such as glucans produced by Cinema Botrytys) however the ability to negatively affect the filling phenomena of the filters is lower.
The characteristics and effectiveness of a gum arabic can be modified by the variation of some parameters such as pH and ionic strength: a lowering of pH for example causes a reduction in the molecular size and consequently in the viscosity.
Gum arabic in winemaking
Since the experiences of Ribereau Gayon in the 1930s, the possibility of exploiting the protective colloid properties of gum arabic has been highlighted in order to reduce the risks of any precipitation of various types (protein, color, metal).
Since the action of protective colloid of gum arabic takes place in synergy with the colloidal structure of the wine, its use is linked to pre-bottling stabilization as a "safety agent" to prevent any precipitation due to instability not previously eliminated.
If used early (on new wines for example) also gum arabic can be an obstacle to precipitations (those following clarification for example, or those caused by refrigeration) necessary to achieve the desired stability in the wine.
This consideration is extremely important as recently preparations for refining wine have been proposed, softness improvers, which in their formulations also contain gum arabic: if used early these can be an obstacle to clarification and precipitation that allow the achievement of stability. of wines.
The action of stabilization with respect to protein cases
In wines, the excess presence of protein substances represents a risk of possible formation of haze and precipitations, which can occur mainly as a result of temperature variations due to phenomena of denaturation of the proteins themselves.
Protective colloids such as gum arabic (or the mannoproteins of the yeast wall) do not eliminate the cause of instability, i.e. proteins, nor do they prevent their denaturation due to temperature variations, but they form a colloidal network that prevents the formation of precipitate particles visible: in other words, very small denatured gum arabic-protein colloidal complexes are formed and therefore not visible in the wine, which appears limpid.
This does not mean that an addition of gum arabic can replace a deproteinizing clarification:
The action of stabilization against metals
Metal ions, such as copper and iron, form colloidal complexes in wine with other substances (sulphides for copper and phosphates or tannins for iron) which, becoming critical in size, can precipitate and cause the formation of deposits (metal cases).
The action of stabilization against color and polyphenolic substances
During their life, both during maturation and in the period of refinement in the bottle, in wine, polyphenolic compounds and anthocyanins undergo, in addition to polymerization phenomena, due to the formation of chemically stable bonds, to colloidal aggregations .
As the aggregates formed by the tannins increase, the equilibrium of the colloidal suspension becomes more and more unstable until, once a critical dimension is reached (which can coincide with the aggregation of tannin with another macromolecule with opposite charge such as a protein), tannin and color precipitate and the phenomenon of “color loss” is observed.
This phenomenon can be accelerated by anything that can somehow affect the equilibrium of a colloidal solution: the presence of metal ions or a sudden drop or rise in temperature for example.
Gum arabic plays an important role in stabilizing the colloidal balance of polyphenolic substances, preventing and limiting the risk of discolouration that can occur after bottling, especially when the wine is destined for long transports or stops in warehouses or display on shelves, where oxidation phenomena can be accelerated by temperature variations and light.
Gum arabic and gustatory characteristics some wine
Thanks to its ability to form colloidal complexes with the polyphenolic substances in wine, blocking the reactivity sites with proteins, gum arabic has a direct influence on the perception of astringency and volume / softness sensations in wines.
In the new colloidal arrangement, the tannins in wine decrease their ability to coagulate the proteins responsible for lubricating the oral mucosa, hence a reduction, thanks to gum arabic, of the sensation of astringency.
On the other hand, the tannin-gum arabic complex is characterized by a greater steric hindrance and this is perceived by the tactile receptors of the oral cavity: the wine will be described as having greater volume and softness.
DID YOU KNOW ABOUT THE IMPORTANCE OF ARABIAN RUBBER IN WINE ???
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