**5.1 'Bio-scouring', the new way**

 The aforementioned disadvantages of scouring with sodium hydroxide has motivated the textile industry to introduce more enhanced biological agents, which would be as effective in removing non-cellulose substances but would not have any damaging effects on cotton and would be less energy and water consuming. As we all know the outer protective coating of the cotton fibre is made up of pectin. The primary aim of any scouring process is to break this outer pectin layer. Once this is broken the cellulose polymers present inside the cotton fibrils are exposed. These have high affinity for water due to abundance of hydroxyl group, thus making the cotton fibre hydrophilic. If there is a way to break this pectin through some other route then the desired scouring effect can be achieved easily.

Pectins, chemically are high molecular weight, negatively charged, acidic, complex branched heteropolysaccharides primarily containing an alpha- (1,4) polygalacturonic acid backbone which can be randomly acetylated and methylated. Contrary to the proteins, lipids and nucleic acids, pectic substances do not have a defined molecular weight. Three different kinds of pectins have been isolated from cotton:

1. Homogalacturonans: These are composed of simple alpha-(1,4) polygalacturonic acid backbone. Some modifications of Homogalacturonans backbone with beta-D- Xylose branching at C3, or apiofuranose substitutions in the backbone with beta-D-Apiosyl- (1,3')-beta-D-Apiose branching are also found. A typical structure of homogalacturonans can be represented as follows:

Pre-treatment of Textiles Prior to Dyeing 227

To break this outer pectin layer of cotton fibre, Pectinase enzymes can be used. In general it can be said that the pectinases or pectinolytic enzymes catalyze the random hydrolysis 1, 4 alpha-D-galactosiduronic linkages in pectin substances. These enzymes are further classified based on the specificity of their reaction sites. Four main types of enzymes are used to break down pectin substances namely protopectinases, pectin esterases, polygalacturonases and pectin lyases. All these three different types have different roles to play in pectin

**Protopectinases:** These catalyze the solubilisation of insoluble protopectin and give rise to

They are classified in to two types based on their reaction mechanism. A-type protopectinases and B- type protopectinases. A-type reacts with the inner site i.e. polygalacturonic acid of protopectin whereas B- type react on the outer side i.e. on the polysaccharides chain that may connect the polygalacturonic acid chain and cell wall constituents. A-types have molecular weight of about 30 KDa. B- types have molecular

Protopectinases Protopectin (Insoluble) + H2O Pectin ( Soluble)

**Pectin Esterases:** These liberate pectin and methanol by de-esterifying the methyl ester

O O

Their activity is highest on 65- 75% methylated pectin, since the enzyme is thought to act on methoxy group adjacent to free carboxyl group. Its action has very little effect on the molecular weight of the pectin. These are highly specific enzymes. Some of them attack only the reducing end while the others attack the non- reducing end. Molecular weights vary in the range of 35- 50 KDa. They are active in the pH range of 4-8. Optimal temperature range

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**Polygalacturonases:** These enzymes directly reduce the molecular weight of the pectins. They catalyze the hydrolytic cleavage with the introduction of water across the oxygen

degradation.

highly polymerized soluble pectin.

weight of about 45 KDa.

linkages of pectin backbone.

for maximum activity is 40- 500C.

bridge.

2. Rhamnogalacturonans I. - This contains alternating alpha-(1-4) galacturonosyl and alpha-(1-2) rhamnosyl residues, with primarily oligo alpha-(1-3) arabinose and oligo beta-(1-4) galactose branching. Atypical structure of it can be represented as follows:

3. Rhamnogalacturonans II. - It is composed of simple alpha-(1,4) polygalacturonic acid backbone with complex branching with composed of up to 11 different monosaccharide types. A typical structure of it can be represented as follows.

2. Rhamnogalacturonans I. - This contains alternating alpha-(1-4) galacturonosyl and alpha-(1-2) rhamnosyl residues, with primarily oligo alpha-(1-3) arabinose and oligo beta-(1-4) galactose branching. Atypical structure of it can be represented as follows:

3. Rhamnogalacturonans II. - It is composed of simple alpha-(1,4) polygalacturonic acid backbone with complex branching with composed of up to 11 different monosaccharide

types. A typical structure of it can be represented as follows.

To break this outer pectin layer of cotton fibre, Pectinase enzymes can be used. In general it can be said that the pectinases or pectinolytic enzymes catalyze the random hydrolysis 1, 4 alpha-D-galactosiduronic linkages in pectin substances. These enzymes are further classified based on the specificity of their reaction sites. Four main types of enzymes are used to break down pectin substances namely protopectinases, pectin esterases, polygalacturonases and pectin lyases. All these three different types have different roles to play in pectin degradation.

**Protopectinases:** These catalyze the solubilisation of insoluble protopectin and give rise to highly polymerized soluble pectin.

$$\text{Protonection (Insolvable)} + \text{H}\_2\text{O} \xrightarrow{\text{Protonpecieses}} \text{Pectin (Soluble)}$$

They are classified in to two types based on their reaction mechanism. A-type protopectinases and B- type protopectinases. A-type reacts with the inner site i.e. polygalacturonic acid of protopectin whereas B- type react on the outer side i.e. on the polysaccharides chain that may connect the polygalacturonic acid chain and cell wall constituents. A-types have molecular weight of about 30 KDa. B- types have molecular weight of about 45 KDa.

**Pectin Esterases:** These liberate pectin and methanol by de-esterifying the methyl ester linkages of pectin backbone.

Their activity is highest on 65- 75% methylated pectin, since the enzyme is thought to act on methoxy group adjacent to free carboxyl group. Its action has very little effect on the molecular weight of the pectin. These are highly specific enzymes. Some of them attack only the reducing end while the others attack the non- reducing end. Molecular weights vary in the range of 35- 50 KDa. They are active in the pH range of 4-8. Optimal temperature range for maximum activity is 40- 500C.

**Polygalacturonases:** These enzymes directly reduce the molecular weight of the pectins. They catalyze the hydrolytic cleavage with the introduction of water across the oxygen bridge.

Pre-treatment of Textiles Prior to Dyeing 229

From the above literature survey, it is very clear that the cotton can be bio- scoured using Pectinases enzyme. As we have seen there is a large pool of sources from which Pectinases enzyme can be obtained and also a huge number of combinations possible depending on the type of pectin degradation required. At Rossari Biotech Ltd, R & D department have developed a bio scouring enzyme named 'Scourenz ABE Liquid', that is successful in producing the desired scouring effects on cotton and its blends. It's a complex mixture of Protopectinases and Polygalacturonases that completes the bio scouring process in 30- 45mins and gives a fabric with absorbency within 4-5 seconds. Lower treatment temperature of 55- 60°C and milder acidic conditions with a pH requirement of 5- 5.5 are the advantages that have proven to be a boon to our customers that are currently using this enzymes.

Saves Wat er Saves Time

Load the material

Bio scouring at 550C for 30 min

Raise temperature of same bath to 900C and hold for 10 min.

Drain

Start Dyeing The actual bio-scouring process takes place at 550C. In this step the pectins are decomposed and emulsified. After bio-scouring, raising the temperature of the same bath to 900C helps in melting of waxes and oils. These released waxes are emulsified at high temperature and the bath is drained. This removes the entire impurities from the bath and the cotton substrate is

The enzymatic process of bio- scouring on bulk scale involves following stages:

Transfer of enzyme molecules from aqueous phase to fibre surface

Adsorption of enzyme molecule on to the substrate surface

The process route that has to be used for carrying out bio scouring operation is:

Saves Energy Economic

**5.2 Rossari's Bio- scouring enzyme – 'Scourenz ABE Liquid '** 

Environment Friendl y

ready for dyeing.

These are the most commonly used enzymes in the market. They are classified further as endo- galacturonases and exo- galacturonases. Endo types are found extensively in nature whereas exo-types occur less frequently. Polygalacturonases obtained from different sources vary widely with respect to their physiochemical and biological properties as well as their mode of action.

**Pectin Lyases:** They also contribute to the depolymerisation of pectin. These catalyse the trans- eliminative cleavage of the galacturonic acid polymer. The lyases break down the glycosidic linkages at C-4 and simultaneously eliminate H from C-5 position, producing an unsaturated product.

In a much simplified way, the action of the above mentioned Pectinase enzymes can be summarized pictorially in the figure given below:

Friendl y

228 Textile Dyeing

These are the most commonly used enzymes in the market. They are classified further as endo- galacturonases and exo- galacturonases. Endo types are found extensively in nature whereas exo-types occur less frequently. Polygalacturonases obtained from different sources vary widely with respect to their physiochemical and biological properties as well as their

O O

O O

O

O

**Pectin Lyases:** They also contribute to the depolymerisation of pectin. These catalyse the trans- eliminative cleavage of the galacturonic acid polymer. The lyases break down the glycosidic linkages at C-4 and simultaneously eliminate H from C-5 position, producing an

In a much simplified way, the action of the above mentioned Pectinase enzymes can be

mode of action.

unsaturated product.

O

O

summarized pictorially in the figure given below:
