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By Dr.Anita Das Ravindranath(Senior Scientific Officer, CCRI ( CORD Vol XVII No.2, 2001)
Coir, the fibre extracted from the mesocarp of the drupe of the coconut palm cocos nucifea is used for the production of beautiful products like mats, matting, carpet, handicrafts etc. (Table 1) Coir suits very well for geotextiles and insulating materials and being environment friendly has and edge over synthetics for application in environmental operations. The world production of coconuts is over 54000 million nuts and although great potential exists in the form of the coconut husk less than 25% is exploited for coir production. Coir can be extracted from the husk by retting or by mechanical extraction. The former process involves retting of the husks yield superior "white fibre" which is in good length, bright in colour and fine texture and ideal for the manufacture of coir products. Mechanical extraction of the husk is instantaneous, however, yields coir fibre that initially is bright coloured but is photoxidised, rendering the fibre of an inconsistent colour . The texture of this fibre is harsh and therefore comparatively extracted fibre is inferior. Retting has disadvantages that it is a prolonged process (nine months), pollutes the retting water through release of phenolic substances, and is a cumbersome process (steeping of and drawing of each husk out from underwater on completion of retting) . It is an established fact that the retting of husk is a microbiological process wherein the binding materials holding the fibres in the husk are biodegraded leading to the release of the fibre. The retting process in a natural system was studied from April to December and the changes occurring in the environment have been elucidated. The pH in the water samples drawn at different stages of retting exhibit a variation, decreasing and increasing to various levels, the minimum pH of 5.5 was recorded in the sample drawn in the fourth month of retting . (Chart 1). The salinity was highest at 10 parts per thousand (ppt) in the month before steeping of husks (Zero) & ninth month decreasing significantly to 1 ppt during the fourth, fifth and sixth months. (Chart 1 ) The polyphenols identified in the water samples collected at different stages of retting are resorcinol, pyrogallic acid and catchall. Application of selected strains possessing phenolytic properties have been successfully conducted to reduce the period of retting of coconut husks to three months, "COIRRETT" a bacterial cocktail has been able to reduce the retting period to three months in the natural retting system and improve the quality of mechanically extracted fibre in 72 hours in RCC tanks . The application of a bacterial consortium grown on husk leachate in laboratory scale studies have been observed to yield encouraging results indicating that coir extraction using biotechnology can eliminate pollution caused by retting The quality of the fibre has been observe to be equivalent to retted fibre as tested for light fastness ratings and degree of softness.
Bleaching process whitens the coir fibre and is conventionally carried out chemical bleaching agents. The application of biotechnology may be well adopted for coir using bacterial and fungal cultures. Bleaching/brightening of coir may not reunite on the fibre surface lignin or the phenolic compounds compounds may be effective if the surface lignin or the phenolic compounds released from the fibre could be destroyed so that the released phenolic compounds may not reunite on the fibre surface and thereby turn more brown. A biotechnological approach to bleaching involves the use of the enzyme xylanase. Fungi naturally produce xylanase to breakdown wood xylans into carbohydrates. The carbohydrates then become the energy source for the organism to grow. The chemistry of xylanse action is not completely clear but it appears to act by chopping up the xylan enough to allow entrapped lignin moieties to escape. It has also been theorized that xylanase breaks lignin moieties to escape. It has also been theorized that xylanase breaks lignin-xylan covalent bonds, thereby releasing the lignin. Therefore microbial cultures eliciting ligninase, xylanase and hemicellulase have potentials for biobleaching of coir.
Coir is a hard fibre with a very high content of lignin 40% and high extensibility (about 37%) which distinguish it from other cellulosic fibres. The high extensibility of the coir fibre is chiefly because the microfibrils in the cell wall lie in perfect helical spirals, extension of the fibre being related with the changes of the spiral angle, that is the angle which a microfibril element makes with the fibre axis. Softening of coir can be attempted by application of biological softening agents, which can modify the surface propertied of fibres and thus improve its physical characteristics and by elimination of the incrusting substance to a desirable extent without adversely affecting the other properties. Microbial enzymes have potentials in bestowing the properties of softness to coir and this remains an area for research yet to be explored in coir .
The decolourisation of coir retting effluents has been successfully carried out using chemical means at the Central Coir Research Institute . The process has been patented and can be carried out in combination with the COIRRET treatment on husks and fibre. Biotechnological means for treatment of coir dyeing and bleaching agents are being experimented at CCRI. The enzymes produced by white rot fungi have potentials for application in this field.
The extraction of fibre from husks liberates huge amounts of dust or "Coir pith " which is lignocellulosic in nature . The lignin in the pith can be biodegraded by lignin degrading microorganisms (Table lll) to yield an organic soil additive with excellent physical and chemical properties. Its bountiful availability and ecofriendly nature renders it as an apt substitute for peat moss.
The principal problem in environmental biotechnology is process control and predictability. In contrast to contained biotechnology involving bioreactors, where the process engineer is able to work with homogeneous or semi-homogeneous systems and to monitor and control all essential parameters, uncontained environmental applications are generally carried out in heterogeneous systems where critical process parameters may be difficult to monitor and even more difficult to control. In such uses, processes are governed , more by ecological parameters pertinent to the particular environment in which the process is carried out . At present in the field of coir, ecological parameters which determine process efficiency are still being and yet to be studied. Quantum increase in performance, predictability, spectrum and safety of environmental biotechnological applications for coir be achieved, through: * elucidation of critical ecological processes which regulate or influence open biotechnological processes * development of genetic tools and strategies to construct performance, and predictable process strains * investigation of the ecological impacts, including possible perturbations, of environmental biotechnology applications. References 1. Abdul Aziz, P.K. and Nair. N.B. (1978) The nature of pollution in the retting zones of the backwaters of Kerala,Aqua,Biol3pp41.62 2 . Das, A.R.1991.Processing of Coir -A biological approach to retting of coconut husks. CORD Vol. Vll, pp.52-57. 3. Das A.R. and Saema U.S, J.Sci. Ind. Res, Application of microorganisms to enhance biodegradation of phenolic compounds and to improve retting of coir .57 (1998)825 4. Kirk, Kent, T. (1984) degradaton of Lignin , In : Gibson, T.D.(Ed) Microbial degradation of organic compounds. microbiology series 13 M.Dekker Inc , New York 5. Mathew M, (1996). Coconut by 2010 AD - Problems and prospects. Proceedings of the National Conference on Coconut, 15 6. Mukherjee, A.K.(1996) Report on the FAO-UN Sponsored Project on Softening , Bleaching, Dyeing and Printing of Coir, Alleppey.
Source: APCC Statistical Year Book 1999 * Revised Fig. Coconut Development Board
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