What are Enzymes?

Enzymes are proteins. Like other proteins, enzymes consist of long chains of amino acid, held together by peptide bonds. They are present in all living cells. Where they perform a vital function by controlling the metabolic process whereby nutrients are converted into energy and fresh cell material. Furthermore, enzyme takes part in the breakdown of food material into simpler compounds. Some of the best known enzymes are those found in the digestive tract where pepsin, trypsin and peptidases breakdown proteins into amino acids, lipases split fats into glycerol and fatty acids, and amylases breakdown starch into simples’ sugars.

Enzymes are basically biocatalysts. Enzymes are capable of performing these tasks, because unlike food proteins such as egg albumin, gelatine or soya protein, they help to catalyze reactions. this means that by their more presence, and without being consumed in the process, enzymes can speed up chemicals process that would otherwise run very slowly, it at all.

Enzymes properties

1. Enzymes are specific

Contrary to inorganic catalysts such as acids, bases, metals, and metal oxides, enzymes are very specific. In other words, each enzyme can breakdown or synthesized one particular compound. In some cases, they limited their actions to specific both in the compound with which they react. Most proteases, for instance, can breakdown several types of protein, but  in each protein molecule only certain bonds will be cleaned depending on the which enzyme is used.

2. Enzymes are very efficient catalysts

The enzymes catalase, which is found abundantly in the liver and in the red blood cells, is so efficient that in one minute. One enzyme molecule can catalyze the breakdown of five millions molecules of hydrogen peroxide to water and oxygen.

3. Origin – natural source

Enzymes are present in all biological systems. They come from natural system and when the are degraded the amino acid of which they are made of can be readily absorber back into nature.

4. Enzymes work only on renewable raw material

Fruits, cereals, milk, fats, meat, cotton leather and wood are some typical candidates for enzymatic conversion in industry. Both the usable products and the waste of most enzymatic reaction are non-toxic and readily broken down Bio – finishing, also called bio-polishing, is a finishing process applied to cellulose textiles that produces permanent effects by the use of enzymes. Bio finishing removes producing fiber and slubs from fabrics, significantly reduces pilling, softens fabric hand and provides a smooth fabric appearance, especially for knitwear and as a pretreatment for printing. In denim processing, Bio-finishing can reduce or eliminate abrasive stone and the aggressive chlorine chemistry.

Bio-finishing is not only useful for cotton but also for regenerated cellulose fabrics, especially for Lyocell and microfiber articles. By incorporating enzymes into detergents to remove protruding surface fibers, improved color retention is achieved after multiple launderings. The disadvantages of bio-finishing are the formation of fiber dust, which has to be removed thoroughly, the reproducibility of the effect and in the worst case, loss of tear strength.

Enzymes are high molecular weight proteins produced by living organisms to catalyze the chemical reaction essential for the organism’s survival. They have complex three – dimensional structures composed of long chains of amino acids (Fig. 1 ) with molecular weights ranging from 10,000 to about 150,000 and occasionally to more the 10,000,00. These naturally occurring molecules provides a high degree of catalytic specificity unmatched by man-made catalysts.

Action of cellulase enzymes on cellulose

Enzymes that hydrolyse cellulose are found in nature in both Trichoderma and Humicola fungi. The  β (1-4) linkage between adjacent repeat unit in the cellulose polymer chain are the sites that are vulnerable to catalytic hydrolysis by celluloses (Fig. 2).

These enzymes are thus able to provide a food source for the organisms by producing glucose from cellulose. Industrial production of cellulose involved large scale growth of fungal populations, followed by extraction of the enzyme. The extracted enzymes contain multiple compound that work together to yield glucose from a cellulose polymer chain. At least four compounds have been identified a being important in providing efficient glucose production.

Endo – glucanases hydrolyse cellulose polymers from the non – reducing end producing glucose and leaving a polymer chain with one less repeat unit. Cellobiohydrolases produce cellobiose from polymer chains, and cello biases convert cellobiose into glucose. These components and their points of attack on cellose polymer chain are shown in (Fig 3 & Fig 4).

Fig. 3: Representation of cellulose fiber internal structure.

Fig.4: Action of cellulases components on cellulose.

Chemistry of enzyme finishing

The enzyme cataysed hydrolysis of cellulose is strongly influenced by factors such as pH, temperature, time and agitation.

The optimal pH for the particular cellulase depends upon its origin. Trichoderma – baed products    ( some time called acid cellulases ) work best at pH 4.5 – 6 whereas cellulose from Humicola (often called neutral cellulases ) are more effective at pH 6 – 6.5. The reaction temperature is also critical since at low temperature, the reaction rate slower than desired, but very high temperature can deactivate the enzyme by providing enough energy to alter its molecular alignments and thereby destroy its catalytic ability. Since enzymes are true catalysts and are not consumed during the chemical reaction, the hydrolysis reaction will continue until either the reaction conditions change or the cellulose is physically removed from the reaction mixture.

Mechanical agitation is important in order for the hydrolysis reaction to proceed efficiently.  Recent work has demonstrated that the Kinetics of the the reaction are controlled by mass transfer effects. The adsorption – desorption mechanism of enzyme action depends on agitation to remove hydrolysis by products and expose new fiber area to attack. Because the enzymes catalytic action is not reduced during the reaction, an effective method of ending the hydrolysis must be employed to prevent excessive fiber loss.

Since the molecule’s physical alignments are crucial to its catalytic ability, procedures that alter the cellulase molecule’s internal structure can be used to deactivate the catalysis and halt the hydrolysis. High temperature (>70˚ C for at least 20 minutes or short drying at 120˚C)high pH (>10) and high electrolyte content as well as enzyme poisons can serve to terminate the reaction by distorting the enzyme’s molecular shape. Recent developments in enzyme manufacturing have led to commercial products.  The contain a preponderance of one cellulose component. These mono – component enzymes are produced from modified Humicola strains and are primarily endo – glucanases active at 7 – 7.5 and are referred to as alkaline cellulases.

Evaluation of bio-finishing 

The removal of cellulosic fiber to improve pilling performance, soften hand, and creating abraded appearance requires not only enzymatic hydrolysis, but also mechanical action to carry out reaction by products physically. Therefore, laboratory evaluations of bio-finished goods can only produce relative rather than absolute results.

Enzyme suppliers determine the activity of their products by measuring the extent of the catalysed reaction under carefully controlled condition. A standard test exist for amalyases  (AATCC Test method 103), but the evaluation of cellulases more complex and can very from supplier to supplier. One common method is to measure the degradation of carboxymethyl cellulose solution. Another is to determine the weight or strength loss of standard cotton fabrics under laboratory conditions where there is a correlation problem, because the mechanical conditions of the technical application are different to the laboratory ones. For example, the hydrolysis degree. HD, is determined by HD = mo – m/mo, Where,  mo  and m are the weight of the test material before and after bio – finishing.

References

1.         Hohberg T and Thumms, ‘Finishing of Lyocell – part 3’ Melliand International,
1999, 5( 1), 83 – 85.

2.         Breier R, ‘Rein enzymatische Antifilzausrustung Von Wolle nach dem Lanazym – verfahrn’ Melliand Textilberichte, 2000,81 (4), 298 – 302.

3.         Stohr R.Enzyme – biokatalysatoren in der Textilveredlung, Melliand Textilberichte, 1995, 76(11), 1010 – 1013

4.         Etters.JN, Annis PA, American Dyestuff Reporter, 1998, 87(5) 18 – 23

5.         Stewart CW,Book of Papers, 1996 AATCC International Technical Conference and Exhibition, Nashville, TN,AATCC, Research Triangle Park, NC, 1996, 212 – 217

6.         Novo’s Handbook of practical Biotechnology, Boyee COL(ed), Bagsvaerd, Denmark, Novo Industries A/S, 1982, 77 – 81

7.         Sarker A and Ethers JN, AATCC Review, 2001, 1(3), 48 – 52

8.         Technical Manual of the American Association of Textile Chemists and colorists, American Association to Textile Chemists and Colorists, Research Triangle Park, NC, 1999. u