Degumming of silk with different protease enzymes

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 21, December 1996, pp Degumming of silk with different protease enzymes M L Gulrajani & Shailja Vaidya Gupta Department oftextile Technology, Indian Institute oftechnology, New Delhi I IO 016 and Abhilasha Gupta & Mona Suri Lady Irwin College, Delhi Received 16 February 1996; accepted 21 March 1996 Silk was degummed with eight different commercially available enzymes, viz. Degummase loool, Protosol, Trypsin, AIcalase, Protease A, Protease N, Pepsin and Protease M. The degumming conditions with respect to concentration and time were optimised for each enzyme. Enzyme activity, an important intrinsic property, and degumming efficiency were evaluated in terms of weight loss, tensile strength, handle and lustre. A weight loss of 24 ± 3% was observed for most of the enzymes at an optimum enzyme cone. of 15% except for Degummase looolwhich gave this result at 25% cone. Trypsin and pepsin gave extremely poor results. The increase in treatment time at the optimum enzyme cone. showed no further significant weight lossthere was no significant strength loss in any of the degummed samples but a marked improvement in handle and lustre was observed. SEM showed that Protosol enzyme gave the best results both with respect to weight loss and smoothness of the fabric. Keywords: Degumming,Protease, Silk 1 Introduction Degumming of silk has traditionally been carried out with soap or alkali. These methods have some major drawbacks, such as the degummed silk obtained is not uniform, the strength loss is high and chemicals used cause environmental pollution. Enzymes are now being considered as alternative degumming agents for the processing of silk. The action of the enzyme can be controlled to avoid strength loss but at the same time obtain a uniformly degummed silk. For this purpose, proteolytic enzymes or pro teases which attack the amide bonds of protein molecule are used. Degumming of silk with protease enzymes has been reviewed by Gulrajani 1. Although, there are reports available where commercial preparations of' proteolytic enzymes have been used to degum silk2 3, no study has been carried out with respect to the enzyme activity and degumming efficiency. In the present study, it has been observed that the activity and the specificity of the enzyme are important factors for degumming with a controlled weight loss of silk. For this purpose, eight different enzymes which.differ in their activity and the conditions under which they act, have been used. These enzymes belonged to three categories, viz. alkaline proteases, neutral proteases, and acidic proteases. Their efficiency with respect to weight loss, strength and overall improvement in the handle and lustre has been evaluated. 2 Materials and Methods 2.1 Materials Bivoltine silk yarn of 35.3 denier was obtained from Bangalore, India. Alkaline protease Degummase loool and Protosol were supplied by Advanced Biochemical Ltd., Bombay, India. Alcalase was obtained from Novo Nordisk, Denmark. Neutral proteases Protease A 'Amano', Protease N 'Amano', and acidic protease Protease M 'Amano' were given by Pfimex Pharmaceuticals Ltd" Hyderabad, India. Trypsin and Pepsin were purchased from Central Drug House (CDH), Delhi,. India. 2.2 Methods Enzyme Activity All the enzymes studied were assayed for activity according to the Anson's method of analysis4 One unit of enzyme activity is defined as the amount of enzyme required to liberate 1!Jogof

2 GULRAJANI et al. : DEGUMMING OF SILK 271 the tyrosine from casein at the required ph at 45 C in 30 min Degumming of Silk Raw silk yarn samples, weighing approximately 1 g each, were conditioned and weighed. The degumming treatment was carried out in Atlas launderometer for 1 h, keeping the material-to-liquor ratio at 1:50. The -samples were degummed to.a weight loss of about 25 ± 2% by the different proteases. The degummed samples were then washed, dried, conditioned and weighed. The recipes used for degumming silk with various enzymes are given in Table 1. In all the cases, 0.1% non-ionic surfactant was also added. The first set of experiments was carried out to optimise enzyme concentration. Samples were treated with different concentrations of enzyme 0.5%, 2.5%, 5%, 10% and 15% (in the case of Deugummase and Trypsin, 25% and 30% cone. were also taken) at optimum ph and temperature for 1h. A control sample in buffer without enzyme was also prepared. This procedure was adopted for each enzyme. Optimum concentration for each enzyme was determined in terms of weight loss. In the second set, experiments were conducted to study the effect of time variation (lh, 2h and 3h) at the optimum concentration determined from the first set of experiments Weight Loss Conditioned samples were weighed accurately before and after enzyme treatment and the weight loss calculated as: Wt.loss (%)= [(~ - "i)/~] x 100 where Wi and Wz are the weights of the fabric before and after the enzyme treatment Tensile Strength The samples obtained under the optimum enzyme concentration were tested for strength using -- - lnstron 4202 Universal Materials Testing System. Peak values of load and elongation were noted and the mean of 20 readings of each was calculated to obtain stress, % strain and Young's modulus ('Y') using the followingformulae: Load Stress=--- New denier where, New denier = Original denier - Denier loss % Denier loss = % Wt.loss Elongation x 100 % Strain = Gauge length Stress 'Y'= Strain Handle and Lustre The untreated control sample and samples treated under optimised conditions with each enzyme were mounted on black chart paper and numbered 1-9. Ten persons were asked to evaluate these and rank them (l-ix) on the basis of handle and lustre separately. Rank I was given 9 points; II, 8 points and so on. Arithmetic mean was computed for each sample and the samples were ranked Degumming Efficiency One yam sample was degummed with Marseilles soap using 25% (owf) soap at'boil for 90 min. Material-to-liquor ratio was kept at 1:50. Taking this as standard 100% weight loss, degumming efficiency of the enzymes was calculated using the followingformula: Degumming efficiency 50mM M- 15% Alcalase NM Protease Trypsin Pepsin O.IM Protosol Table I-Recipes O.1M (owf) 15% (owf) M A used for deguming silk with various enzymes Degummase % Wt.loss by enzyme treatment x 100 % Wt. loss by soap treatment

3 272 INDIAN J. FIBRE TEXT. RES., DECEMBER 1996 Enzyme conc.,o/o (x) _ Nil :7 SEM Studies Filaments of samples treated under optimised conditions and those of the untreated sampl~ were scanned using a Cambridge scanning electron microscope. Table 3- Regression equations for weight loss Regression equation R RZ RZ SE of estimate Yl = x Yz= x r Y3 = x r Y4 = x-0.037r Ys= x xz Y6 = x x2 3 Results and Discussion The effect of enzyme concentration on weight loss of silk yam is shown in Table 2. In order to find out the co-relation between weight loss and 30 enzyme concentration, regression analysis was carried out. The regression equations and correlation coefficients for all the enzymes investigated are given in Table 3. With the help of the regression equations, graphs between the two variables were plotted (Fig. 1). Except in Degummase, 20 ~ ~ 52~ 3:.. 10 '0) which showed a linear relationship between weight loss and enzyme cone., in all other enzymes the relationship was best represented by quadratic equation. 6 o LOSSALC o 15 ~LOSSDG ~LOSSPM LOSSPA LOSSPN From the measured weight loss the following observations can be made: A weight loss of 2.3% at 0.5% Degummase concentration was observed which increased to 22'% at 25% enzyme concentration. The value of standard error of estimate (0.825) was lowest for Degummase enzyme. Also, the coefficient of correlation was the highest(r= 0.988). Both these coefficient factors implied highest accuracy in prediction among the nine enzymes used. Degummase (DO) was the only enzyme that required a higher enzyme concentration, i.e. 25%, to achieve over 20% weight loss. The enzyme was used in alkaline conditions and was the only enzyme for which linear correlation was observed between weight loss and enzyme cone. Protosol (PR), another protease functional under alkaline conditions, gave a weight loss of 25% at 15% enzyme concentration. The degumming ef- o o Fig. I-Effect of enzyme concentration on weight loss ficieqcy of this enzyme was better than that of the Degummase enzyme. A high correlation coefficient and low standard error of estimate made the results predictable with a fair accuracy. Alcalase (ALe), the third enzyme in the alkaline buffer category, showed weight loss of 7.35% at -,..,- I Concentration, % x LOSSPR

4 GULRAJANI et al. : DEGUMMING OF SILK 273 Protosol Alcalase (PR) (ALe) A (PA) Degufnmase (DG) Protease N M (PN) (PM) 0.5% enzyme concentration which increased to 26% at 15% enzyme concentration. This enzyme was found to be the most effective in the complete removal of sericin. Also, the results were fairly predictable with high correlation coefficient (R=0.968) and low s.tandard error of estimate (1.674). When compared to the different enzymes used, the extent of sericin removal with the alkaline buffer category enzymes was found to be maximum. Protease A 'Arnano' 2 (PA), a neutral buffer enzyme, gave a good correlation value of and standard error of estimate, A weight loss of 22% at 15% enzyme concentration was obtained. The other neutral enzyme Protease N :.\mano' (PN) gave the lowest correlation coefficient and highest standard error of estimate among the set of enzymes studied. The results of this neutral protease could be predicted with least accuracy. A weight loss of 22.45% was obtained at 15% enzyme concentration. The enzymes in the neutral buffer category were not as effective degummingagents as compared to other enzymes. Among the acidic proteases studied, Protease M 'Amano' (PM) showed a high weight loss of 25% at 10% enzyme concentration. Moreover, correlation coefficient was and standard error of estimate was 1.105, which implied fairly high accuracy in terms of prediction. Trypsin (TRY) and Pepsin (PEP) enzymes showed exceptionally poor results of 4% weight loss at 30% and 15% enzyme concentration respectively. In general, as can be observed from Table 2 and Fig. 1, an increase in the enzyme concentration shows a marked increase in weight loss. A weight loss of 24 ± 3% was observed for most of the enzymes at an enzyme concentration of 15% except for Degummase which gave the general result at 25% concentration (Table 2). Two exceptions to the general trend were the enzymes trypsin and pepsin which gave extremely poor results. After having optimised the concentration of the enzymes at a constant time of lh, the time was varied at the constant optimised concentration., The increase in the treatment time from Ih to 3h showed no further significant weight loss (Table 4). The silk yam with a weight loss of 24 ± 3% was tested for strength loss, handle and lustre.' There was no significant strength loss in any of the degummed samples (Table 5). However, in general, the alkaline proteases gave more consistent results where strength was concerned. These samples also showed a marked improvement in the handle and lustre as seen by the average ranking given in Table 6. The scanning electron micrographs (Fig. 2) of these samples also substantiate the above results. The treatment with alkaline proteases results in the complete and uniform ram()'\181of sericin. Amongst the alkaline proteases, Protosol enzyme gave the best results both with respect to the weight loss and the smoothness of the fabric obtained (Figs 1 & 2b). The neutral enzymes also gave fairly good results although the removal of the sericin was not very uniform (Figs 2f & 2g).. Micrographs obtained after treatment with acidic enzymes (Trypsin and Pepsin) showed as expected poorly de- Table 4-Effect of treatment time on weight loss of silk yarn Enzyme Weight loss, % 2h 3h Ih Table 5-Effect of enzymatic degumming on tensile strength [Gauge length, 50 mm; Speed, 10 mmi s; Initial load < 1.00 g] Sample Tensile strength Elongation Modulus glden % glden Control Degummed with Degummase (25%) Protosol (15%) Alcalase (15%) ProteaseA(15%) Protease N (15%) Protease M (15%) Pepsin (15%) Trypsin (30%) Table {;i~effect of enzymatic degumming on, handle and lustre Sample Rank Handle Lustre Control VI v Degummed with Degummase ill IV Protosol n ni Alca1ase I Protease A V V ProteaseN IV ill ProteaseM vn IX Pepsin vn VII Trypsin IX VllI

5 ~ ~ z o >= z ~ 'Tj 53 :::0 >< :-l ~ Y' ott1 (") tt1 ~ I:;l:l tt1 :::0... \0 \0 0-. Fig. 2-Scanning electron micrographs of silk yarn degummed with Degummase (a), Protosol (b), Alcalase (c), Protease A 'Amano'(d), Protease N 'Amano' (e), Protease M 'Amano' (f), Pepsin (g), Trypsin (h), and Control (i) ~ ~ ~ A...

6 GULRAJANI et al. : DEGUMMING OF SILK 275 ~~ Table 7-Activity Enzyme Degummase Protosol Alcalase Protease A ProteaseN ProteaseM Table 8-Degumnring efficiency of enzymes Degumming agent Wt.lQSS Degumming /~ efficiency, % Marseilles soap Degummase (25%) Protosol (15%) Alcalase (15%) Protease A (15%) Protease N (15%) Protease M (15%) Pepsin (15%) Trypsin (30%) of enzymes Activity AU/mg gummed samples with considerable amount of sericin still remaining on the surface (Figs 2h & 2i). To analyse the degumming efficacy of the different enzymes under similar conditions of enzyme concentration (w/v), it was important to determine the activity of the enzymes. The activity of the individual enzymes as obtained by the Anson's method is given in Table 7. According to these results, enzymes having activity of more than 3400 AU/mg were the most significant degumming agents, giving degumming efficiency of more than 80% when compared with the 100% j degumming obtained with Marseilles soap (Table! 8~ ' Interestingly, Protease 'M' which has. comparatively low amopnt of enzyme activity of 745 AU/ mg (Table 7) showed a good degumming efficiency of 92.96% (Table 8). One probable reason for this aberration could be due to the specificity of the enzyme. This can cause the ~me to attack only certain specific regions of the sericin, resulting in high weight loss but non-luliform removal of the sericin. This observation was further supported by the fact that the highest coefficient of variation of strength measurements (0.267) was observed for this enzyme. This is an indicator of uneven degumming and the presence of thick and thin sections in the.degummed sample. Thus, to use an enzyme as an effective degumming agent it is important that the activity of the enzyme should be taken into consideration before evolvinga protocol for the use of enzyme. References 1 Gulrajani M L, Rev Prog Color, 22 (1992) Chopra S, Garg S & Gulrajani M L, Korean J Sene Se~ 36(1 )(1994) Chopra S & Gulrajani M L, Asian Text J, January (1994) Anson M L, J Gen Physio~22 (1939)