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Enzymes are biological catalysts. They are called catalysts because their main job is to speed up and control reactions in the body but they themselves remain unchanged at the end of the reactions. They change the rate of reactions so that it's suitable for our body.
Enzymes are globular proteins; their molecules form a precise three-dimensional shape, with hydrophilic R groups on the outside of the molecule to ensure that it is soluble and hydrophobic groups on the inside. Enzyme molecules also have a region called the Active site. The active site is like a depression on the molecule to which another molecule can bind. This molecule is the substrate of the enzyme and the active site is designed so that the substrate fits perfectly into it. This combined structure is called the enzyme-substrate complex.
When the enzyme-substrate complex has been formed the enzyme may either catalyze the breaking down of the substrate or the joining together of two molecules. The outcome is the product. Just like normal catalysts, Enzymes are not used up after reactions; they can be used again and again as long as they are not denatured. Enzymes can be denatured by many things but the main one is heat. Enzymes can only work best at a certain optimum temperature, above this, the molecules of the active site of the enzyme shift and it becomes unstable. All metabolic reactions in living organisms are catalyzed by a specific enzyme. Since these reactions take place in different conditions like pH, the enzymes are adapted to also work best in these conditions.
Enzymes in Industries
Enzymes are useful as catalysts because of many properties: Enzymes speed up reactions, work in mild temperatures and are fairly easy to control; therefore they are used in many industries like wine making.
Although enzymes are useful they enzymes can be denatured by temperature and the organic solvents which often have to be used in industrial processes. Enzymes can also be inhibited by the products of the reaction. Enzymes are also expensive to produce
Enzymes used industrially are generally extracted from living organisms like Microorganisms, plants and animals. But microorganisms are preferred because of many reasons like: they have high growth rates and carry out a wide range of chemical reactions.
There are many enzymes involved in wine making including pectinases. Pectinases occur naturally in all fruit, including grapes, and are in part responsible for the ripening process. Grape Pectinases are however inactive under the pH and SO2 conditions used in winemaking. However, Fungal Pectinases are resistant to these winemaking conditions.
In order to get Pectinases form Aspergillus niger, it must grow on pectin as a carbon source. Therefore the Fungi needs to be stimulated to produce the desired enzymes and their side activities and will produce very little if grown on a normal sugar source like molasses. Only genetically modified fungi can grow on other substrates and still produce the desired enzymes but this is because they are genetically manipulated to continually produce the enzyme, they do not require a specific substrate to stimulate enzyme production. The structure of the enzyme produced in this way is not different from the structure of the enzyme produced by the un-manipulated organism, this is because the enzyme itself is not modified - only the organism used in the production is, and the organism is removed from the final product.
Pectinases in winemaking
Pectinases can be used for settling
After being crushed, negatively charged pectins make a protective layer around positively charged grape solid particles. This helps to keep the grape solid particles in suspension so that pectinase enzymes can break the pectin molecules into smaller products, allowing some of the positively charged grape solid particles underneath this protective layer to be exposed. These positive charges bind to the negative charges of the grape solids that are protected by pectin and bigger particles form. When the particles become too big they settle out.
These settling enzymes mainly react on the soluble pectins like homogalacturonans of the pulp of grapes. The skins of grapes have more insoluble pectin called protopectin with more "hairy regions" which are actually side chains. Therefore, skin contact enzymes together with the settling enzyme components have much more side activities that specifically work on the side chains of the pectin. Just like all fruits, the structure of pectin changes during the ripening of the grapes and as a result they become softer. Grapes that have become very ripe require settling enzymes with higher concentrations of PG. When problems are experienced when using very ripe grapes, skin contact enzymes should be used because they contain more polygalacturonase (PG).
Skin contact enzymes
The structure of the insoluble pectin in grape skin cell walls is more complex than the pulp soluble pectins. It is because of this reason that skin contact enzymes are used in high concentrations and contain essential side activities. Skin contact is performed to extract juice and aroma. The cell walls of grapes make up a physical barrier between the juice in the vacuole of the cells of the berry and the outside. Since the cell walls of grape cells contain about 30% pectin, pectinases are therefore used to break this physical barrier and therefore increase juice yield.
Most grape aromas are found in the skins of the grapes. Skin contact increases their concentration in the must. An adapted white skin contact enzymatic formulation is specially designed to contain reduced levels of cellulases and hemicellulases in order to avoid over soaking of the grape skin (maceration).
Red wine making enzymes
Enzymes used in the maceration stage in making red wine may contain hemicellulase for much better maceration. Enzyme formulations used in making red wine should also contain very low concentrations of anthocyanase activity, which breaks off sugar molecules from more complex sugar molecules. Grape anthocyanins are stabilized by the covalent linkage with one glucose unit. They become unstable when these linkages are broken.
The above example shows the vinifera anthocyanins molecule, with a sugar in the 3- position.
Using pectinases in Wine making is much more economical friendly and is generally more suited than other catalysts that may be created. This is because the help increase the yield of juice extracted from grapes and they help improve the quality of the colour extraction process when making red wine. Enzymes also offer improvements in the ageing process of the wines and this helps enhance the flavor.