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Biotechnology in jute fibre processing: An eco-friendly approach

As a result of improper retting, average grade of jute is invariably associated with varying portion of under-retted barky root ends with runners and specks throughout the reed of the fibre. Fibres of such quality stand in the way of producing fine yarns and fabric. Fortunately, scientists working in Biology Division of Indian Jute Industries’ Research Association (IJIRA) have constantly explored the biotechnological route to process jute fibre in an eco-friendly manner.

Jute is the second most common natural fibre, next to cotton, cultivated in the world. It is extensively grown in Bangladesh, China, India, Indonesia, and Brazil. Within India, jute is an important commercial crop of eastern states. The jute fibre is obtained by a natural microbiological process known as “retting” from the bark of two cultivated species of corchorus, namely, C. capsularis. L. (white jute) and C. olitorius L. (Tossa jute).

Another allied fibre of jute, known as ‘kenaf’ in most part of the world also has good demand. In India, kenaf is known by two commercial names “mesta” and “bimli” according to its regional origin and is usually grown in less rainfed areas under fibre cultivation. South India based jute mills, by and large, depend on bimli/mesta fibre obtained from hibiscus cannabinus and hibiscus sabdarifa. Mesta on the other hand, is grown in the upper eastern regional states of India. Over the years, there has been substantial increase in acreage and production of jute in the country.

Although current annual average production of 85-90 lakh bales of jute (baile = 180 kgs) out of which approximately 20 per cent accounts for mesta or bimli, is indeed impressive in terms of quality of fibres. One of the main reason for poor quality is improper retting of jute at the post-harvest stage of fibre production which again is often due to lack of sufficient clean water. Research and development efforts in this direction have made marginal impact in real terms. However, persistent efforts have led to the growth of quality awareness among farmers.

Problems in jute processing

As a result of improper retting, average grade of jute is invariably associated with varying portion of under-retted barky root ends with runners and specks throughout the reed of the fibre. Fibres of such quality stand in the way of producing fine yarns and fabric. Poor spinning and weaving productivities of jute mills in turn hamper the cost competitiveness of the ultimate jute products in local as well as export markets. Having said this, it naturally becomes important to briefly mention the traditional method of jute processing as has been practiced over the last several years.

Jute fibre is first softened with oil in water emulsion and piled in organised heaps (called morah piling) for a period ranging from 24-72 hours usually, depending upon the quality of fibre. During piling, temperature within the pile rises upto 50-60ø C due to the exponential growth of natural microbial flora mainly bacteria and fungi in the aerobic and anaerobic phases. Micro-environment of the pile is extremely complex and some enzymes are produced by the microbes. The resultant fibre becomes soft to some extent. The piled jute fibres are then passed through various carding and drawing stages to make them ready for spinning and later on weaving. During earlier times the whale oil (marine origin) has been reported to be used for preparation of emulsion for softening. Economic realities of the times probably forced a replacement of this oil of natural origin in absence of environmental awareness. The mineral oil (petroleum origin) that became popular as Jute batching Oil (JBO), primarily due to its cheapness, thus remained a major fibre lubricant in subsequent years.

The environmental obligation and sustainable process development

Jute fibre is an annual renewable natural resource. Secondly, it is completely biodegradable. The rate of biodegradation is of course expected to vary under various geoclimatic as well as agroclimatic conditions. Thirdly, jute products after completing its lifecycle can be recycled also. These three properties combined with its relative low cost, makes jute the most ideal material. So jute fibre, in its own right, has started regaining the lost market not only in the area of packaging in general and food packaging in particular, but has started finding endless diversified uses.

Since jute fibre is naturally endowed with above properties it makes sense that a fibre of biological origin must be treated and processed only with biological agents to bring desirable attributes to improve spinning as well as weaving productivity to produce yarns, fabrics and products of better quality for sustainable growth and development of the jute industry in the years to come. Scientists working in Biology Division of Indian Jute Industries’ Research Association (IJIRA) having strong conviction in this ecological ethics, have constantly explored the biotechnological route to process jute fibre in an eco-friendly manner. Biotechnological method developed at IJIRA for jute processing involves biological agents such as live bacteria and fungi and extracellular enzymes produced by them.

Microbiological activities in a jute pile during processing is not sufficient to bring about desired softness. Attempts were therefore made to supplement bacterial culture in liquid to completely utilise the jute cuttings. The softening effect expected of the added bacteria was found to gradually decline. A mixed co-culture of bacteria and fungus grown on wheat bran was found better than the bacterial potato culture.

This was followed by production of extracellular enzymes by isolated fungal strain and application of the crude enzyme extract during piling. Thus, gradually biotechnological foundation for application of enzyme in jute processing was laid in the jute industry.

Application of enzyme in jute industry

For enzyme based proven process technologies developed at IJIRA are currently in use in the Indian jute industry. Research impetus that led to the development were either provided by the jute manufacturers and consumers or raw material shortage due to various environment factors. The target aimed at were cost-reduction, quality improvement, diversified jute products development and above all customer satisfaction.

Enzymatic softening and upgradation of jute fibre

The concept of using enzymes and not living microorganism, as an aid to softening low grade fibre in the pile started in the biology division of IJIRA with research work on fibre softening enzymes way back in mid-1970s. As mentioned earlier, the downgrading of jute fibre is the result of incomplete retting of jute plants with residual pectin - liemicellulase gum occurring on the strands of such fibre and barky root ends. The thickened root ends of low grade jute are under-retted barks comprising dried cell of parenchyma tissue held together. Taking a cue from the chemical composition of jute fibre and bark, the hydrolytic enzymes needed to soften and decompose certain unwanted carbohydrates were assigned for this purpose eg, cellulose, hemicellulase, pectinases, xylanases, etc. As the hydrolytic degradation of tissue proceeds for which requisite moisture must be supplied, the bacterial action also begins simultaneously and is accelerated by the easily assimilable reaction products (glucose, xylose) generated by enzyme action. The synergistic effect of the two biological systems, enzyme and bacteria, brings about ideal softening of barky tissue, no matter how hard it may be, in the minimum period of piling. The enzyme system developed at IJIRA never showed any perceptible damage to jute yarns even when applied in higher concentration during trial in the pilot plant at IJIRA as well as in mills. As a pleaisant surprise, a cellulose inhibitor was detected in the enzyme system during investigation which specifically blocks the fibre degrading effect of cellulose and restricts its action only on the surface of the fibre. The presence of this in-built cellulose inhibitor reported for the first time from IJIRA makes IJIRA’s enzyme system a safe instrument for bio-softening, and upgrading of jute fibres. Experience after years of application of the system in mills fully corroborates this.

Although the restricted action of cellulose is necessary to soften jute, the softening effect is, however, realised through the action of hemicellulase, enzyme and important component of the IJIRA’s enzyme system. Henicellulose occurring in association with lignin in the primary will of fibre cells, spread over the outer periphery of the filament is hydrolysed by enzyme. Once this gummy hemicellulose is partially decomposed, further generation of pliability on fibre is achieved by the concurrent action of cellulose. As a result of enzyme action smooth separation of finer filaments from the mushy structure is obtained during subsequent carding operation. The resultant fleece is more lustrous and clean, so much so that slivers obtained from low grades fibres softened enzymatically can be spun at a significantly higher efficiency to produce better quality of yarn. Choice of application of enzyme in a given situation varies from mill to mill and according to different periods of the year. Guidance to mills is provided by IJIRA consultancy services where a judicious application of regimen is provided after considering all variables. For example, at the beginning of the jute season, when fresh supply of raw jute is available emphasis is generally laid on increase in spinning productivity whereas towards the end of the jute season upgradation of lower grades of jute is recommended to maintain the spinning productivity which tends to slide down.

Retention of moisture in sliver and yarn is a general problem in mills during the dry seasons and the spinning productivity is drastically effected. Application of enzyme during dry season helps to retain more moisture by at least two per cent. This is because enzymes also act as a swelling agent and causes transverse swell of fibre. In other words, enzymes help to convert the process-free moisture to bound moisture. The rate of evaporation of bound moisture is always lower than the free moisture thereby moisture is retained in slivers and yarn during processing. Thus retention of moisture during processing is one of the major advantages of using enzyme in jute processing.