17.16 Enzymes for fabric conditioning and processing, and food processing

There are many uses for fungal enzymes in the food industries, some of which we have described, but there are many other aspects of both clothing and food manufacture that depend on enzymes produced by fungal cultures. Industrial enzymes are estimated to be worth somewhere in the region of US$ 2.0 billion annually to these industries. The textiles industry is very large and lucrative, and even with the successful emergence of synthetic fibres such as nylon and polyester, a great many of our fabrics are still made from natural fibres like cotton (cellulose) fibres and wool and silk (protein) fibres which can be processed in various ways with natural enzymes.

The fabric processing with which we are individually most familiar is that resulting from the inclusion of fungal enzymes in detergents used for clothes washing. Enzymes included in biological detergents must be active under alkaline conditions: they include proteinases, lipases, amylases (used to remove protein, grease and sugar soiling) and cellulases (for colour brightening and fibre restoration). Some of these enzymes are derived from bacterial sources, but many are fungal enzymes.

Enzymes are also used during manufacture of textile products. Emerging areas of development include:

  • Enzymatic preparation of natural fibres; biopreparation allows the removal of impurities prior to dyeing and saves water, natural fibres can also be modified to produce value-added products (for example the addition of silk peptides to wool), and surface modification of wool fibres to improve the feel of the final fabric. Hydrolytic enzymes including pectinases, cellulases, proteinases, and xylanases have been applied to cotton processing, resulting in fabrics with good absorbency that feel soft to the touch.
  • Enzymatic bioprocessing of synthetic fibres, increasing functionality and adding value of polyester, polyamide or acrylic fibres.
  • Remediation of textile effluents; bioremediation and effluent processing are important aspects of fabric processing, and enzymes can help here, too, for example laccases decolourise waste dyes.

Cellulase treatment of cotton fabrics is an environmentally friendly way of improving the property of the fabrics. Although cellulases were introduced into textile manufacture only in the 1990s, they are now one of the most frequently used group of enzymes for these applications. Cellulases have proved so popular because of their ability to modify cellulosic fibres in a controlled manner that improves the quality of the fabrics.

When biofinishing cotton fabrics with cellulases, loose fibres are removed more efficiently and more gently than mechanical methods can achieve. An interesting application is in the preparation of ‘stone-washed' denim by a process known as biostoning. The textile industry is, of course, a fashion industry and for some years it has been fashionable for denim clothes to have a worn, faded, look and be soft to the touch. Traditionally, denim jeans manufacturers have washed their garments with pumice stones to achieve these desirable features, hence: stone-washed jeans.

The disadvantages of using stone for washing denim garments included damage to equipment by tumbling stones, difficulty of removing residual pumice from processed clothing, and particulate material clogging drainage channels. The still fashionable aged look is obtained by combining cellulase enzyme treatment with some form of mechanical distressing such as beating or friction. Using cellulase immobilised on a pumice carrier has advantages and can both reduce process costs and raise the activity of the enzyme (Pazarlioğlu, Sariişik & Telefoncu, 2005).

Many of the treatment and finishing processes in the wool industry require chemicals that are environmentally unfriendly, particularly treatments aimed at reducing shrinkage of wool garments. Traditional treatments require strong acidic chlorine and results in polluting wastes. This generates interest in the use of enzymes to achieve the same effects on wool. A range of proteolytic enzymes are the candidates but they penetrate and degrade the internal wool structure during processing, causing unwelcome fibre damage. Natural enzymes can be modified or immobilised to control fibre degradation by enzymes, pointing the way to successful development of enzymatic treatments for achieving a variety of finishing effects for wool-containing products (Shen et al., 2007).

Enzymes are also used extensively in food biotechnology. Several examples feature elsewhere in this chapter. As an example here we note that the production of apple juice is the largest in the juice industry after grapes, and in order to maximise the yield of extracted juice, enzymes are incorporated into the procedure. This is common feature among a wide variety of sectors in the commercial food processing industry as they increase the output of product without additional capital investment.

Processing apples utilises macerating enzymes, pectinases, cellulases and hemicellulases (Table 11; Bhat, 2000), in two separate steps: extraction and clarification. The enzymes are used in the extraction to liquefy the fruit, increasing the yield of juice collected and enhancing release of other important cell ingredients such as antioxidants and vitamins. In the second step the enzymes are used to remove any precipitates that are formed from insoluble pectin.  Because the enzymes are mixed with the juice, the two need to be separated before packaging and distribution. This is usually achieved by adding gelatine as a fining agent which causes the enzymes to clump together in ‘flocs’ which can then be removed by filtration. One problem with this process is that the enzymes are used only once. Immobilisation of enzymes on polysaccharide gels, nylon filter membrane or particulate carriers enables them to be recycled (Alvarez et al., 2000).

Table 11. Cellulases, hemicellulases and pectinases in food biotechnology.

Enzyme

Function

Application

Macerating enzymes (pectinases, cellulases and
hemicellulases)

Hydrolysis of soluble pectin and cell wall components; decreasing the viscosity and maintaining the texture of juice from fruits

Improvement in pressing and extraction of juice from fruits and oil from olives; releasing
flavour, enzymes, proteins, polysaccharides, starch and agar

Acid and thermostable pectinases with polygalacturonase, pectin esterase and pectin transeliminase

Fast drop in the viscosity of berry and stoned fruits with the breakdown of fruit tissues

Improvement in pressing fruit mashes and high colour extraction

Polygalacturonase with high
pro-pectinase and low cellulase

Partial hydrolysis of pro-pectin

Production of high viscosity fruit purees

Polygalacturonase and pectin
transeliminase with low pectin esterase and hemicellulase

Partial hydrolysis of pro-pectin and hydrolysis of soluble pectin to medium sized fragments; formation and precipitation of acid moieties; removal of hydrocolloids from cellulose fibres

Production of cloudy vegetable juice of low viscosity

Polygalacturonase, pectin transeliminase and hemicellulase

Complete hydrolysis of pectin,
branched polysaccharides and mucous substances

Clarification of fruit juices

Pectinase and β-glucosidase

Infusion of pectinase and
glucosidase for easy peeling/firming of fruits and vegetables

Alteration of the sensory properties of fruits and vegetables

Arabinoxylan modifying
enzymes (endoxylanases,
xylan debranching enzymes)

Modification of cereal arabinoxylan and production of arabinoxylo-oligosaccharides

Improvement in the texture, quality and shelf life of bakery products

Cellulases and hemicellulases

Partial or complete hydrolysis of cell wall polysaccharides and substituted celluloses

Improvement in soaking efficiency; homogeneous water absorption by cereals; the nutritive quality of fermented foods; the rehydrability of dried vegetables and soups; the production of oligosaccharides as functional food ingredients and low-calorie food substitutents and biomass conversion

β-Glucanases and mannanases

Solubilisation of fungal and bacterial cell wall

Food safety and preservation

Xylanases and endoglucanases

Hydrolysis of arabinoxylan and starch

Separation and isolation of starch and gluten from wheat flour

Pectin esterase with no
polygalacturonase and pectin
lyase activities

Fruit processing

Production of high quality tomato ketchup and fruit pulps

Rhamnogalacturonase
Rhamnogalacturonan acetyl
esterase and galactanase

Cloud stability

Production of cloud stable apple juice (cloudy juices that do not sediment in storage)

Cellulase and pectinase

Release of antioxidants from fruit and vegetable pomace

Controlling coronary heart disease and atherosclerosis; reducing food spoilage

Endo-mannanase

Modification of guar gum

Production of water-soluble dietary fibres to enrich the fibre content of foods

Table modified from Bhat (2000).

The microbial enzymes used for industrial processes are largely produced by liquid fermentation  but solid state fermentation has great potential for the production of enzymes (Pandey, 2003). For example, enzyme preparations from Phanerochaete chrysosporium, Aspergillus oryzae, Aspergillus giganteus and Trichoderma virens, produced by solid-state fermentation on cotton seed-coat waste (which serves as both substrate and enzyme inducer) produced enzymes that could be used effectively to degrade impurities in cotton fabrics during biopreparation (Csiszár, Szakács & Koczka, 2007).

The search continues for new enzymes from other organisms by screening microorganisms sampled from new environments or developed by modification of known enzymes using protein engineering or recombinant DNA technology (Olempska-Beer et al., 2006).

Updated December 17, 2016