Enzymes used in textile manufacture
Enzymes are being increasingly used in textile processing for the finishing of fabrics and garments, especially in desizing, biopolishing and denim washing.
Prior to weaving fabrics from cotton, or blends of cotton and synthetic fibres, the threads are reinforced with an adhesive (termed ‘size’) to prevent breakage of warp threads. The size may be composed of starch, starch derivatives, vegetable gum and water-soluble cellulose derivatives, such as methyl- and carboxymethylcellulose.
Before dyeing, bleaching and printing, the size must be removed from the cloth. This has previously been accomplished by treatment with acids, alkalis and oxidizing agents that may damage the fibres. Consequently, enzymatic desizing with amylases or cellulases is now widely used, as they are non-corrosive and produce no harmful effluent wastes.
Cellulases are also employed in bio-polishing cotton and other cellulose fibres to produce fabrics with a smoother and glossier appearance. Similar processes using microbial proteases have been developed for treating wool fibres, which are composed of keratin.
Treatment of denim garments to give a worn look before sale is called ‘stonewashing’. Traditionally, this has been accomplished by washing the garments in a tumbling washing machine with pumice stones. Cellulases are now used to accelerate abrasion and aid the loosening of the indigo dye. This ‘bio-stonewashing’ is less damaging to the garments, reduces wear on machines and generates less pumice dust.
Enzymes used in leather manufacture
Proteases and lipases are now extensively used in the processing of hides and skins. These enzymes are easier to use, more pleasant to handle and safer than the harsh chemicals that were previously employed. Their most important applications are in soaking, dehairing, degreasing and baiting. Soaking is the first important operation of leather processing.
Apart from cleaning the hides and skins by removing debris derived from blood, flesh, grease and dung, it rehydrates them. Proteases enhance water uptake by dissolving intrafibrillary proteins that cement the fibres together and prevent water penetration. Lipases are also used to disperse fats as an alternative to degreasing with solvents. These enzymes hydrolyse surface fats and those within the structure of the hides and skins, but without causing any physical damage.
Dehairing of hides and skins has traditionally employed chemicals such as slaked lime and sodium sulphide, which have in the past made tannery effluent a severe pollution problem. Enzyme-assisted dehairing involves proteases, often the alkaline protease from Aspergillus flavus. Their use reduces or totally replaces the requirements for chemical processing and provides a major cost reduction in effluent treatment.
Leather baiting prepares the leather for tanning. It involves removal of any remaining unwanted protein to make the grain surface of the finished leather clean, smooth and fine. Traditional methods employed dog, pigeon or chicken manures. These were very unpleasant to use, unreliable and slow, and have been replaced by microbial proteases.
Enzymes used in the treatment of wood pulps
Paper manufacture is a major world industry. In the USA alone over 70 million tonnes of paper and paperboard are manufactured each year, which have a value in excess of US$50 billion. Paper manufacture involves the processing of mostly virgin fibres, but there is increasing utilization of some recycled materials or secondary fibres. Recycling saves both trees and energy, decreases waste effluents and reduces landfill loads.
Traditionally, wood pulp processing has involved the extensive use of chemicals, which can lead to problems with effluent treatment and environmental pollution. Thus, the development of enzyme-based technology for pulp processing and paper manufacture has major advantages.
Microbial enzymes can be used in several stages of pulp and paper processing to:
- Enhance pulp digestion.
- Improve drainage rates in water removal during paper formation.
- Increase fibre flexibility.
- Selectively remove xylan without affecting other components.
- Remove resins.
- Enhance bleaching.
- Remove contaminants, such as in the de-inking of high-quality waste paper.
- Fibrillate or increase interfibre bonding in chemical pulps and herbaceous fibres.
Those microbial enzymes used in these processes include a wide range of cellulases, hemicellulases, pectinases and lipases. However, they cannot yet replace all mechanical and chemical treatments.
Enzymes as catalysts in organic synthesis
There is a rapidly growing market for microbial enzymes used in the synthesis of high-value organic compounds for the chemical, food and pharmaceutical industries. One commercially valuable area involves the application of cyclodextrin glycosyltransferases, often obtained from extreme thermophiles, to create cyclodextrins from simple starch molecules. These cyclodextrins are useful carriers of fragile compounds such as vitamins and flavours. No chemical means exists for creating this class of substances, so the enzymatic route is unique.
An increasingly important field is the synthesis of chiral compounds. Chiral compounds exist in two forms called enantiomers, which are non-superimposable mirror images of each other and are therefore asymmetrical. In virtually all respects, the two enantiomers are physically and chemically identical.
However, solutions of one enantiomer rotate the plane of polarized light in a clockwise direction (+), whereas solutions of the other enantiomer rotate it anticlockwise (-), but by exactly the same amount. This phenomenon is known as optical activity and enantiomers are sometimes referred to as optical isomers.
Chirality is vitally important in biology as most natural organic compounds are chiral. For example, most amino acids are enantiomeric, with only one enatiomer usually being found in nature. However, when the compounds are chemically synthesized an almost 50: 50 mixture of enantiomers is made, which is called a racemic mixture. Usually, for most biological molecules, as for amino acids, only one of its variants or enantiomers is biologically effective as an enzyme substrate, pharmaceutical drug, nutrient, etc. Its other enantiomer may be useless/futile or even damaging to health.
The reason that identical molecules of opposite chirality can have such different biological behaviour is that proteins, especially enzymes, and nucleic acids are themselves chiral molecules. Consequently, any drug or nutrient must have the proper chirality if it is to interact with a protein of specific chirality.
In the industrial synthesis of such compounds, there have to be controls to guarantee the production of only the desired enantiomer, often at a purity higher than 99%. Not only is it economically disadvantageous to make a large quantity of chemicals when only half (one enantiomer) is biologically functional, but for some drugs the other enantiomer may be toxic. Certain chiral syntheses can be performed chemically, but enzymic routes are usually preferred.
Enzyme-based processes can be used to prepare specific enantiomers and resolve enantiomers from racemic mixtures. These processes utilize racemases, which are a family of enzymes that accept either enantiomer, although they are themselves chiral like all other proteins. Their biological function is to turn a substrate of one chirality into its opposite form. They can be used to synthesize chiral amines, alcohols and many other compounds.
Reference and Sources:
- https://textilevaluechain.in/news-insights/fibres-yarns-news/enzymes-in-textile-a-sustainableand-
greener-approach#:~:text=Enzymes are widely used in the textile industry,of chemical
reactions without undergoing any change themselves. - https://www.researchgate.net/publication/320957279_Current_Scenario_of_Industrial_Biotechnology_in_India
- https://leatherenzymes.weebly.com/soaking.html
- https://chiralpedia.com/blog/introduction-to-chirality-understanding-thebasics/#:~:
text=Chiral synthesis (enantioselective synthesis, also called asymmetric
synthesis),the formation of a specific enantiomer or diastereomer. - https://pmc.ncbi.nlm.nih.gov/articles/PMC6233012/
- https://openpress.usask.ca/intro-organic-chemistry/chapter/4-6/
- https://open.maricopa.edu/fundamentalsoforganicchemistry/chapter/5-3-
chirality/#:~:text=Rotation of plane polarized light by a chiral,rotate light in equal magnitude
but opposite direction.
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