Central Research Institute for Jute & Allied Fibres, Barrackpore, Kolkata-700120, India

B. MajumdarSenior Scientist

Microbial Retting of Raw Jute

What is retting ?• The process of separation and extraction of fibres from non-fibrous

tissues and woody part of the stem through dissolution anddecomposition of pectins, gums and other mucilaginous substance iscalled retting.

• The microorganisms, mostly bacteria from retting water enter the planttissues through the stomata, epidermis and cambium or the cut end,when immersed in retting tank, and through their enzymatic actionloosens the fibre strands from the woody core.

• The fibres are then mechanically extracted, washed, dried andmarketed. The whole process is known as retting

• If retting is properly carried out, the extracted fibre should exhibitgenetic quality of the variety.

• Improper retting may lead to bad or inferior quality of fibre in spite ofgood crop which ultimately may result in lower net return to thefarmers.

Mechanism of Retting

• Absorption of water by jute plants and liberation of solubleconstituents like sugar, glucosides and nitrogenous compounds fromjute plants favouring initial microbial growth.

• Further, these microbes utilize free sugars, pectins, hemicellulose andproteins of the plants as essential nutrients for their development andmultiplication under the favourable condition.

• Secretion of specific enzymes like pectinase, hemicellulase or xylanaseby microbes and degradation of the respective complex organicmaterials.

• The decomposition of free sugar present in jute and mesta plantstakes place at early stage of retting, followed by pectins during middlestage, and hemicellulose, sugars and nitrogenous compounds (mainlyproteins) at later stage of retting

Methods of Retting

• Conventional method of whole plant retting

• Chemical Retting• Microbial Retting• Mechano-microbial Retting• In-situ retting with microbial consortium

Conventional method of whole plant retting

• Under this method, defoliated jute bundles are steeped in clean orstagnant water according to the availability with proper jak materials.Most of the farmers used mud or banana logs as jak resulting in darkcoloured fibre leading to less net income.

• To avoid the discolouration of fibre seasoned wooden logs, cementedpoles, brick bats tied in cement bags can be used as jak materials andcovering materials should preferably be water hyacinth or coconutleaves.

• When the retting of jute is completed in 18-21 days, fibre is extractedmanually by “beat-break-jerk” or single plant extraction method.

A typical “Jak” of Jute bundles for retting

Defoliated jute bundles is steeped in clean water

Farmers’ Practice

Farmers’ Practice

Conventional retting using mud and banana plant as covering material

Farmers’ Practice

Conventional retting using cemented ring as covering material

Improved Practice

Improved Practice

Use of cemented bags filled with sand/ soil as covering material

Fibre extraction under conventional method of retting

Drying of dark coloured jute fibre

Chemical Method of Retting

• Boiling with acid, alkali or with some salts at specifictemperature for 6-8 hours.

• Washing of degraded products with clean water

• Removing excess liquor by drying

• Breaking the retted and dried stalks

• Retting process may be accelerated by chemicals like urea,ammonium oxalate, calcium sulphate and magnesiumphosphate.

• The fibres obtained are little coarser, rough in the feel andstiff

What is the need?

• Slow moving soft water produces best quality fibre, but suchconditions are rarely prevailed in the jute growing areas of India.

• The conventional whole plant retting method of jute and mestadoes not suit to the farmers under water crisis situation.

• In recent years, it has been found that due to lack of rainfall duringthe retting period particularly in West Bengal, jute growers wereforced to ret their jute in muddy water leading to the inferior qualityjute fibre and less net income.

• So, there was an urgent need to develop an improved method ofretting which - requires very less amount of water, lesser time thanconventional method, improves fibre quality, and above all which isuser-friendly and eco-friendly in nature.

Actual situation during water scarcity

Ground water is the only source in case of low rainfall.

Ground water table goes down.

More water will be needed to saturate the soil.

Artificial retting tank (cemented or polyethylene lined) is theonly option to hold water for long time.

Where is the retting microbes?

Addition of retting microbes from out.side

What is the Task?

• Pectin and hemicelluloses (22-25%) are the main binders present inthe primary wall and middle lamella of the cell.

• The major task in extraction of jute fibre is to remove these non-cellulosic substances from the bast without damaging the fibrecellulose.

• The task for development of microbial consortium for jute rettingneeds such microbes those are having very high pectinolytic as wellas xylanolytic activity without any cellulolytic activity.

How to Proceed?

• Collection of retting water sampleRetting water samples were collected from high and mediumproductivity as well as Good-quality jute fibre producing districts ofWest Bengal. Retting liquor was collected between the jute bundlesin the ‘jak’, where the growth of microorganisms are likely to bemaximal.

• Isolation of pectinolytic microbes Pectinolytic bacteria were isolated by serial dilution and plating onYeast extract-pectin agar and grown for 48 hrs at 340C. Colonieswere then selected and replica plated. One of the replica plate wasflooded with 2% cetrimide and washed with 1M NaOH. Coloniesgiving detectable halo zones and having a potency index (halo zonedia./colony dia.) greater than 3 were selected for enzymatic study.

Halo zone Formation

How to Proceed? Contd.

• Estimation of Pectinase activityPectin lyase activity was estimated by reducing sugar estimation(Dinitro Salicylic acid reagent method) method with D-galacturonicacid as calibration standard at 535nm using three differentsubstrates namely polygalacturonic acid sodium salt, citrus pectinand apple pectin.

• Estimation of xylanase activityThe screened isolates having very high pectinolytic activity werefurther tested for their xylanase activity. For degradation of xylan,the screened isolates producing clear halo zones on xylan agar wereselected. Assay of xylanolytic activity was done by reducing sugarestimation method with 3,5- Dinitrosalicyclic acid using xylan assubstrate and D-xylose as calibration standard.

How to Proceed? Contd.

• Estimation of Cellulase activityThese isolates were further screened for cellulolytic activity. Bothqualitative (halo zone formation after flooding the colonies on CMCagar plate with congo red) and quantitative estimation by reducingsugar estimation method with 3,5-dinitro salicylic acid, using D-glucose as calibration standard, confirmed the absence of cellulolyticenzymes.

• Screening for antagonismThese promising isolates were further screened for antagonism byusing standard method. The isolates screened out for makingefficient retting consortium produce cellulose free- pectinase,xylanase and found compatible with each other.

Compatibility test of selected isolates for making consortium

Isolate (*3) does not permit other isolates to grow on its lawn

Isolate (*3) can grow on the lawn of other isolate but does not allow

others to grow properly

How to Proceed? Contd.• Screening for Synergism

Finally the isolates were applied in all probable combination andtested for pectin degrading capability. Out of all possiblecombinations, a combination of three isolates was found to be veryeffective for jute retting purpose.

• Identification and Molecular CharacterizationThe isolates were then identified by using Biolog. Molecularcharacterization of these isolates were done by 16S rDNAsequencing (ribotyping) of a 977 base pair fragment. These threeisolates were found to show 99 % maximum identity in individualBLAST analysis.

• Patent DevelopedCRIJAF has filed a patent application to the patent office, Kolkata on“A Microbial Consortium Used in Faster Retting of Jute & Mesta”(Appl. No. 418/KOL/2011, dated-30/3/2011)

Microbial Retting

1. Microbial retting consortium can be used for efficient

retting either for ribbon retting or whole plant retting

during water scarcity situation utilizing minimum amount

of ground water.

2. There are two improved techniques of microbial retting

developed by CRIJAF are a) Mechano-microbial retting and

b) In-situ retting of whole plant jute.

Mechano-microbial Retting

Mechano-microbial retting of jute involves two distinctoperations viz.

i) Mechanical extraction of green ribbons through eitherpower operated bast fibre extractor suitable for jute, mesta,sunnhemp and ramie or manually operated jute fibreextractor and

ii) Retting of green ribbons with microbial consortium.

Mechanical Extraction of Fibre• The power operated bast fibre extractor can extract 25 kg dry fibre

per hour with broken sticks while manually operated jute fibreextractor can extract 15 kg dry fibre per hour with unbroken sticks.

• This machine is light in weight, portable, easier to operate andcheaper too.

• Considering the optimum plant population of jute as 4.5 lakh /ha,three machine days are required for extraction of ribbon from 0.6lakh plants in one ‘bigha’ (1 ha = 7.5 bigha) of crop. Therefore, 0.2lakh plants are to be fed to the extractor each day.

• Five plants of optimum basal diameter (1.5 cm and above) can befed to the machine at a time. Around 15% of the plant populationbeing thin and lanky, 10 such plants can be fed to the extractor at atime.

• Thus number of feeding per machine per day works out to be 3700times [(17000 optimum plants 5) + (3000 thin plants 10)]which is practically feasible.

Working Module• The green ribbons extracted immediately after harvest by either of

the two extractors developed by CRIJAF, i.e. power operated bastfibre extractor or manually operated jute fibre extractor

• These ribbons are then treated with the microbial consortium with acfu (108 to 1010 ) @ 100 ml/10 kg of green ribbons and kept for 1hour covering with polythene sheet.

• For small scale, in polythene lined retting tank of 1 M3 size (1m x 1mx 1m) containing 1000 litres of water, 2 q of green ribbons can beput at a time for efficient retting.

• These sprayed ribbons are steeped vertically in polythene lined pitsfor retting and retting is completed within 5-7 days.

• The fibre is then washed in clean water and dried.

Extraction of green ribbons by using manually operated jute fibre extractor

Extraction of green ribbons

Spraying of microbial consortium to green ribbons before steeping in retting tank

Machine extracted ribbons are dipped in polyethylene lined retting tank after spraying of retting consortium

Dried fibre ready for marketing

Advantages of Mechano-microbial retting

• This method requires less volume of water (1: 5) compared to 1:20under conventional method.

• Total fibre production is more compared to conventional whole plantretting, where a substantial portion of fibre is lost during retting andwashing.

• Retting is completed within 7-9days in comparison to 18-21 daysrequired under conventional whole plant retting.

• The fibre quality is improved at least by 2 grades (from TD6 to TD4).

• The net income is increased by at least Rs. 3000 to 4500/ha thanconventional method if the average yield is 30 q/ha.

In situ Jute Retting with microbial consortium

• A circular micro pond of 6.5 m floor diameter and 7.5 m topdiameter and 1 m deep having 1 m wide earthenembankment lined with polyethylene sheet (800 to 1000gauge, 30 ft x 27 ft) is sufficient to ret jute/ mestaharvested from 1333.3 M2 (one bigha) land.

• The sharp bases of the jute plants have to blunted byramming the bundles on hard surface to avoid damage tothe polyethylene sheet.

• A single layer of straw bundles arranged radially at thebottom of the pond over polyethylene/tarpulin sheet toavoid damage to the polyethylene sheet

In situ Jute Retting contd.• Harvested jute bundles are arranged radially up to three layers

keeping base of the plants towards periphery of the pond.

• Microbial consortium with a cfu (108 to 1010 ) was then applied tothe jute bundles in the pond.

• Under ground water was then added to the retting tank and the jutebundles are then covered with straw/aquatic weeds.

• For proper immersion of the jute bundles in the water cement bagsfilled with sand, brick or soil can be put above the jute bundles.

• After retting, the fibres have to be washed in the retting pond itselfafter removal of 50 % retted water and addition of fresh water in thepond.

• The fibres are then sun dried on the embankment of retting pond.

Micro pond for in-situ jute retting

Radial straw arrangement along periphery

Radial arrangerment of jute bundles in micro retting tank

Application of under ground water in micro retting tank

Application of microbial consortium on jute bundles

Well ret jute bundles under straw jak

Fibre extraction at the micro pond

Washing of fibre at the micro pond

Diversion of nutrient rich water from retting tank to rice field for irrigation

Golden coloured and lustrous fibre obtained from micro pond is ready for marketing

Growing of vegetables on the embankment of retting tank

In situ jute retting: Advantages• Retting is completed within 12 to 15 days compared to 18 to 21 days

under conventional retting.

• Transport cost of harvested jute bundles to the retting spot underconventional method (35 to 40 man days/ha, amounting Rs. 3500 to4000) will be eliminated in this method.

• The pond can be used for fish cum paddy culture after retting.

• The quality of fibre will be improved at least by 2 to 3 grade.

• The famer will be benefitted by Rs. 5000 to 6000/ha overconventional method as the fibre yield is around 35 q/ha.

• The pond embankment can be utilized for plantation of high valuevegetable crops (early cauliflower, cabbage, brinjal, tomato andcapsicum etc.), which will compensate the cost of polythene.

Changes in chemical properties of retting water samples (whole plant retting

Source of retting water Chemical analysis of retting water samples

pH Ca+ Mg

(me/l)

Cu

(ppm)

Fe

(ppm)

Mn

(ppm)

K

(ppm)

Initial water sample aftermixing microbialconsortium

8.1 3.70 0.03 - 0.144 4.3

Whole plant after rettingwater sample 1

7.7 14.52 0.36 - 0.074 91.9

Whole plant after rettingwater sample 2

7.9 10.78 0.39 - 0.034 141.0

Whole plant after rettingwater sample 3

7.3 28.20 0.42 - 0.035 169.0

Jute Retting and Environment• Jute assimilates about 5.8 ton CO2 from the atmosphere in its life time

(Rahman and Bala, 2009)

• Life cycle assessment of jute production systems revealed that theconventional retting practice emits a little bit more nutrients, biogasand residues to the air and water compared to ribbon retting.

• A wide variation in the rate of production of methane ranging from 8to 779 mg M-2h-1 and averaging 148 mg M-2h-1 was measured atseveral sites in West Bengal.

• Total methane generation from jute production is estimated to be18.8 x 1010 g per year, a small fraction of the estimated methanegeneration from rice fields. (Banik et al.1992)

Conclusion• Slow moving soft water produces best quality fibre, but such conditions

are rarely prevailed in the jute growing areas of India.

• Scarcity of water or low rainfall during retting time compels farmers to rettheir jute crop in stagnant muddy water resulting in low quality jutefibre.

• Under such situation, mechano-microbial retting process developed byCRIJAF proves to be suitable for farmers.

• By this process, farmers can ret their jute crop after ribboning within aperiod of 7-9 days in very less quantity of water with improvement infibre quality and more net income than conventional method of retting.

• In-situ jute retting in micro pond with microbial consortium is anothersuitable option left for jute farmers as an alternative to conventionalmethod of retting in less time, reduced volume of water with qualityimprovement.