a comparative study of two wool enzyme...
TRANSCRIPT
Indian Journal of Fibre & Textile Research Vol. 27. December 2002, pp. 408-416
A comparative study of two wool enzyme treatments
P Jovancic & D Jocic
Textile Engineering Department, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Yugoslavia
and
R Molina, A Manich, R Sauri, M R Julia & PErra"
Instituto de Investigaciones Quimicas y Ambientales de Barcelona,
Consejo Superior de Investigaciones Cientiricas, Jordi Girona 18-26- 08034 Barcelona, Spain
Received 22 May 2001; revised received 29 October 2001; accepted 10 December 2001
The influence of enzyme concentration and treatment time on certain wool properties has been studied according to the Box-Hunter experimental design in order to better understand the wool modirieation caused by two different enzymatic multi-purpose formulations (enzyme A and enzyme B). It is observed that enzyme concentration and treatment time exert an influence on wool whiteness. shrink resistance, weight loss and urea bisulphite solubility. The enzy me concentration has a decisive influence on wool modirication when enzyme A is applied, and on the treatment time when enzyme B is applied. Tensile strength properties and SEMs suggest that enzyme B can attack the non-keratinic parts of wool fib re structure. No significant degradation of cortical or even cuticular cells is observed after enzyme A treatment. Accordingly, enzyme A could be applied all over the experimental zone whereas in the case of enzyme B, the enzyme concentration over 5% and treatment time over 60 min should be avoided. FTIR/ATR analysis confirms that there is no significant change in the redox state of cystine disulphide bonds at the wool surface after the enzyme treatment.
Keywords: Enzymes, FTIRlATR study, Physico-mechanical properties, Scanning electron microscopy , WOo)1
1 Introduction There is currently an increased demand for
environment-friendly wool treatments as an alternative to the conventional wool treatments that produce AOX byproducts. The use of enzymes to achieve wool shrink resistance, better whiteness and improved handle is of considerable interest l
-7
• Shrinkresistant wool is the major priority but if enzymes are applied at levels that provide the required shrink resistance, the wool fibres are often unacceptably damaged owing to irregular treatments. R, 9. Enzymes alone or in combination with hydrogen peroxide are also successfully employed in wool bleaching lO
, as auxiliary agent in wool dyeing" ·1s, for wool handle modification by reducing wool fibre stiffness and
. kl 16 17 d . lb" 18 pnc e . , an III woo car omzlllg . However, the knowledge of the specific action of
enzymes in substrates with a heterogeneous morphological structure and a chemical composition, which are characteristics of wool, is still unsatis-
3 To whom all the correspondence should be addressed. Phone: 34934006165; Fax: 34932045904; E-mail : [email protected] ic.es
factory , ]t is apparent that the results of enzymatic treatments, especially with proteases, can be unpredictable and may lead to unacceptable degradation of wool fibre. Consequently, it is essential to restrict the enzymatic action to the wool fibre surface or retard its action to avoid the enzyme diffusion into the wool. In other words, the enzymatic action on wool must be completely controlled3
, The correct experimental design and statistical methods for analysis of the results can be very useful tool in investigating wool enzymatic treatment8
,
From both technical and practical points of view, it is often useful to optimize the enzymatic treatment conditions before its industrial use. The present work was, therefore, aimed at determini ng the influence of different commercially available enzyme multipurpose formulations on selected wool properties. To this end, the effect of enzyme concentration and treatment time on the degree of whiteness, weight loss, urea bisulphite solubility and area shrinkage was investigated. The results were evaluated by a central rotatable design to follow the complex experimental conditions with more accuracy 19, Moreover, it was
JOVANCIC ('/ (II .: A COMPARATIVE STUDY OFTWO WOOL ENZYM E TREATME TS 409
expected that thi s approach should permit the objective eva luation of so me similarity and di fferences between the enzy mes used. Tensi Ie strength properties of enzy matica ll y-treated wool were also measured. Chemi cal and morphological changes in the fibre surface were in vesti gated by FTIR/ATR spectroscopy and SEM respectively.
2 Materials and Methods 2.1 Materia ls
The knitted wool fabri c (Pulligan International S.A. , Spain) with a cover facto r of 1.22 tex 112/rnm was cleaned by Soxhlet ex trac tion with dichloromethane, rinsed with ethanol and water and equilibrated in a conditioned room (20°C, 65%RH). Two speci tic enzy me multi -purpose formulations were employed in this investigation: (a) Bactosol WO (Clari ant Iberica, Spain), a biocatalyst based on selected enzy mes (new type hydrolase) which acts specifically on protein fibres, leading to proteolys is, esterolysis, lipolys is and keratinolys is (hereinafter ca lled enzyme A); and (b) Bio~oft PW (T. S. Chemicals, U K), a preparation of proteolytic enzy mes proteases (hereinafter ca lled enzy me B). All other chemicals and auxiliaries were of laboratory reagent grade.
2.2 Methods 2.2. 1 Enzyme Treatment
Enzy me treatments were carried out by exhaustion method at a liquor-to-wool ratio of L5: I. The treatments were performed in round-bottomed flasks by thermostatica lly-controlled shaking bath OB 14 (Memmelt, Germany) at 55°C and pH 9 using a Na2CO,/Na HC03 buffer. The level of ag itation was low during the treatment. After the treatment, the wool samples were hand squeezed, rinsed in HCI at pH 4 for 5 min to stop the enzymatic action, then rinsed twice in distilled water and finally dried in air on a flat sLlli·ace.
2.2.2 Experimental Design
The experimental levels of applied enzy me concentrati on ( 1-8 % o.w.f.) and treatment time ( 15-105 min) were calcul ated in accordance with the BoxHunter central rotatable ex perimental des ign (Table I). The complete central co mpos ite rotatable design for two vari ables at fiv e ex perimental levels requires thirteen experiments and includes five repeated experiments carri ed out to obta in an est imate for the wi thin-t reatments variat ion 19. 21l. Further detai Is about the central rotatab le experimental design, analysis of the measured responses fo r each experi mental condit ion, as well as the mode of obtaining the
TGb ic I - Expcrimcnla l va lucs or vari ablcs ror dilTercnl codcd Icvc ls
Variablc Codcd Icvel
- 104 1 - I 0 + 1 +1.-+ 1
Enzymc concentration (XI). % 2 4.5 7 8
TrcGtmclll timc ex:!) . min 15 30 60 90 105
adju sted pol ynomial equations and so-called isoresponse (contour) diagrams can be found in the li teraturex. 19,2 1.
2.2.3 Tests
Degree of whiteness (CI EGanz 82) was measured using a spectrophotometer Color-Eye 3000 (Macbeth , USA) with D65 illuminant and 10" observer. The hi gher the va lue of the degree of whiteness, the more white is the wool. Weight loss was dete rmined on samples conditioned for at least 48 h at 20"C and 65 % RH. The results are ex pressed as the percentage of the weight loss of the treated sa mp les compared with an untreated sample. Urea bisulphite so lubility (U B solubi lity) was determined in accordance with U E 40.20572. It was ca lculated as the percentage of weight loss of the wool sample treated for 60 mi n with 50 ml of a standard urea bisulphite so lution at 65"C. Area shrinkage was determined according to Wool mark TM 3 1 by the Wascator model FOM 7 1 washing machine using ISO 6330 SA wash cyc le programme as a base to determine the total felting shrinkage of wool samples22
. When the area shrin kage is lower than 8% after two SA cycles, the wool can be considered as machine washable23.
The chemi ca l changes on the wool surface we re determi ned usi ng a FTI R Spectrophotometer 5 10 (Ni co lel, Germany) in the ATR refl ec ti on mode with KRS-5 45" crystal. The spectra were normali zed aga inst the peak intensity of 1232 cm' l (amide III ). The peak intensity of each selected band frequency ( 1040, 1075 and 11 24 cm' l ass igned to cysteic ac id, cystine monox ide and cyst ine dioxide respecti vely) were compared with the corresponding peak in tensity of untreated wool 24 .
For SEM observat ions, untreated and enzy mat ically -treated wool samp les were accordingly sputtercoated with a thin layer of gold and viewed at 15kY in the scanning electron microscope (Model 570, Hitachi , Japan).
Yarn tensile strength was determined using an Instron 5500R Tensil e Tester in accordance with ASTM D 2256-80. Twenty repeated measu rements per sa mple were carried out and the res ults were
4 10 IND IAN J. FIBRE T EXT RES., DECE MB ER 2002
ex pressed as tensile strength at max imum load rather than as load at break.
3 Results and Discussion The compl ete ex perimental des igll and the results
obtained for the degree of whiteness, urea bisulphite solu bility, weight loss and area shrinkage fo r enzy me A and enzy me B as well as for the untreated sample are given in Table 2.
To obtain the regress ion coeffi cients and adjusted polynomial eq uati ons containing onl y the vari ables with a signifi cance above 95%, the multiple regress ion analys is and anal ys is of vari ance
(A NOY A) were employed with the aid of a computer program specially made for thi s purpose. Based on the data from the regression coeffi cients and adjusted polynomi al equati ons, the isoresponse di agrams as projecti ons of the response surfaces were drawn. The adju sted polynomi al equations obtai ned for both enzy matic treatments are given in Table 3.
The res ults indicate that wool wh iteness, when compared with that of untreated wool, is enh anced for all the combinati ons of enzy me co centration and treatment time (Table 2). As can be seen in Fi g. 1, the whiteness is improved by increas ing enzy me concentration and treatment time. The increase is
Tabk 2- Expc ri lllc nt al co nuiti ons and results obtained fo r the pa rameter!,
Ex p.
no.
2
3
4
5
6
7
8
9
10
II
12
13
I
2
3
4
5
6
7
8
9
10
II
12
13
Leve l of va ri abk
Coded
- I - I
+ 1 - I
- I + 1
+ 1 + 1
- I A I 0
+ I A I 0
o - I A I
o + I A I
o 0
o 0 o 0 () 0
o 0
- I - I
+ 1 - I
- I + 1
+ 1 + 1
- IAI 0
+ 1.4 1 0
o - I A I
o + I A I
o 0 o 0 o 0
o 0
o 0
Experi menta l
XJ x:!
% min
2
7
2
7
8
4.5
4.5
4.5
4.5
4.5
4.5
4.5
2
7
7
I
8
4.5
4.5
4.5
4.5
4.5
4.5
4.5
30
30
90
90
60
60
15
105
60
60
60
60
60
30
30
90
90
60
60
15
105
60
60
60
60
60
Untreated sa mple
"Compa red to the untreated sample
Response
Whi teness C IE UB Weight Ga nz 82 Solu bility, % loss", %
Enzy mc A
-4.8
-2 .2
- 3.7
2.2
- u I A
--u - 1 2
- 1.7
- 3.0
- 3A
- Ul
- 3.2
E nzymc 13
1 5
5.8
8. 1
13.8
4.4
11.7
4. 1
8.9
8.5
8.9
9.0
10.2
8.9
-5.3
5 1 5
54.2
50.9
55.9
49.2
50.2
54.8
52.5
54.0
54 .1
no 54.5
52.7
58.9
60.0
60. 1
05.0
57.3
62.0
57.4
60.8
6 1.2
60. 1
60.3
59.9
60.5
49.5
OAO 0.82
1.04
1.65
0 .58
2.07
0.89
1.28
1.25
1.30
1.26
1.20
11 0
1 67
2.2 1
5. 13
6.78
2A2
5. 15
1.39
5.9 1
3.78
3.93
3.88
3.9 1
3.97
Area shri n"age. %
SA Wash cycles I 2 3
27.9 44 .2 55.0
30.4 45.0 54.5
24 .7 44.2 52A
26.0 42.8 53.5
27A 45.7 54.5
30.5 38. 1 58.6
29. 1 44.0 55.8
26.0 45A 66.3
29.7 48.8 58 .9
24.5 49.3 54.0
28.9 48.9 58.7
29.0 49.9 58 .6
32A 49.5 596
28. 1 44.2 54.5
26.3 42.4 5 1.7
22.6 40.n 50.3
23.8 37.6 46.8
26.7 43. 7 52.6
19.6 37.S 45.6
29A 42 .6 54.5
22. 1 37.3 47.6
2 1 5 37 .5 46.5
24A 39.6 53.4
19.5
24.8
22.3
33.8
38.~i
39.3
40.0
57.0
46.5
50.5
49. 1
63 .9
JOVANC'I C CI 01.: A COM PARATIV E STUDY OF TWO WOOL ENZY ME TR EATMENTS 4 11
Table 3- The adjusted pol ynomial equal ions for the parameters
Response
Whiteness
UJ3 solub ility
Weight loss
Area shri nkage
En/.ymc A
-2.48+ 1.56.11+ 1.29.1",+ 1.07.11' R=O. S9 /?2=O.77 S.I:: .=1.38 F-ral io=4.70
53.66+2.20.11-0.48.1'1' +0.55.11.1'2 R=0.94 /?2=O.88 S.E.=0.8 1 F-rat io=2 1.0 I
1.22+0. 39.1'1+0 25.1c 1?=0.91 /?c=O.i·n S.E.=0.2 1 l'-rati o= 14. 14
49.3 1- 1.4 11'1-3.5].1'1' -2 .09.\"/ /?=O.93 /?'=O.P,7 S.I::.= 1.44 1:- r:lli o= 19.34
Enzy me B
9.14+2.54.\·1 +2 .68.l'c- I.33xI2 R=O.96 R' =O.93 S.E.= I.IO F-rali o=24.9 1
60.40+ 1.59.\"1+ 1.35.\"2+0.%.1'1 .1, I?=O.92 R'=O.85 S.E.=O.98 F-rat io=7.98
3.89+0.76.\"1+ 1.8o.I'2+0.27.r1.\"2 R=0.99 R' =().97 S.I::.=O.30 F-r:lti o= IIO.93
]'11,.99-1 .57.\"1-2.0(l.\2 2 + 1.07.1' 1' R=O.04 R' =(UN S.[ .=0.07 F-ralio= 16.9:1
R- Multipl e corre lation coe ffi cient: R2- Coe lTi eic nt of delermination: S.E.- Slanda rd error of esti mation: and F-ra li o- Test variance/Error va riance
(0 )
15LL __ ~~~~~~~~~~~~'
f ! • ;
(b)
! I I
j
1 2345678123 t.. 5 G 7 8 Concentration of enzyme: %
Fi g. I- Whiteness degree obtained after treatmelll with (a) en7.yme A; and (b) enzyme B
more pronounced w ith enzy me 8 , indica ting that it is more effect ive than enzyme A (Fig. I b) . At the central point of experimental design (experiments from 9 to 13 in Table 2) , the whiteness after trea tment with enzyme 8 is considerably superi or to that obta ined after treatment with enzyme A, the difference being 11 .62 CIE units (Tab le 3) . This could be attributed to enzyme efficiency in el i mi nati ng the natural-co loured pigments of the wool surface which are bonded to the wool protein and lie mainl y in the cuticle layer2
. II.
The enzymatic treatments were on ly partially effective in relation to wool shrinkage reduction. The effect was slightly improved by increasing enzyme
. d . dS 7 'S A concentration an treatment tllne, as reporte .. . -. . comparat ive analys is of the shrink res istance obtained after treatment with enzymes A and 8 is shown in
Figs 2a and 2b. It can be observed that wool shrink res istance after the enzyme treatments is fai rl y comparab le. However, at a higher enzyme concentrati on and at a longer treatment time, the shrink-resist effect obtained by enzyme 8 IS
approximately 10% higher than the effect obta ined by enzyme A (Tables 2 and 3).
It is clear that enzyme 8 is more effecti ve than enzyme A not on ly in regard to whiteness improvement but also in regard to shrink res istance. However, this effect is assoc iated with excess ive fibre damage, expressed as weight loss (Figs 3a and 3b), and urea bi sulphite solubility (Figs 4a and 4b). 80th the parameters increase when the treatment time and enzy me concen tration are rai sed. It is well known th at urea bisulphite so lubility of wool decreases as a result
4 12 INDIAN J. FIBRE TEXT. RES., DECEMBER 2002
(G) ( b )
lO S
90 c .....
E OJ E
'';:;;
60 C CD
E (I)
OJ
~ 30
"2 3 4 6 7 B 2 ] t.. 5 Concentration of enzyme, %
~ ....... "
········'37.5 ., .. ". ,.··· .. -·,,·/ .,;
...... , .... , ...
\.
6
."' ..... ......
..•.
... ...
. r·· .. ··
7 8
hg ,2- Area shrinkage obtained arter 2x5A Wascator shrin kage test cyc les after treatment with (a) e nzy me A; and (b) cnzy mt: B
( 0) ( b )
90 .r:;
2 4 5 G 7 8 2 J '4 5 6 7 Concentration of enzyme, %
Fi g,3- We ight loss obtai ned afte r trea tment with (a) enzy me A; and (b) enzy me B
105
90 c E ai 75 E
;;;; - 60 c (j)
E. ro 45 OJ L. .-
30
15 2 3 t. S
Concentration of enzyme, %
Fig.4- Urea bisulphite solubility obta ined al ter treatme nt with (a) enzy me A; and (b) enzyme B
JO VANC IC e l al.: A CO MPARAT IVE STUDY OFTWO WOOL ENZYM E TREATMENTS 4 13
of alkaline treatments due to lanthi onine and Iys inoalanine fo rmation26 and increases because of the d I b 'd 'd' . ry7 ryx I amage causec y aC I s or OX I ISing agcnts- . - . n this case, increased urea bi sulphite solubility after the enzy me treatment is probably due to hydroly sis of some of the wool peptide and isodipeptide bonds.
The results show that in the case of enzy me A, the concentration exerts a dec isive influence on wool whiteness, urea bi sulphite solubility , weight loss and shrinkage properties, whercas in the case of enzyme B, the treatment time plays an important ro le (Tables 2 and 3). Bearing in mind that a weight loss of 3-4.S % could be excessive for wool5. 10 , it is clear that enzy me A could be appl ied all over the ex perimental zone. By contrast, in the case of enzyme B, the concentrati on over S% and treatment time over 60 min should be avoided.
The SEMs of wool treated under different conditions generall y show that the enzy mati c treatment is not uniform. Some fibres can be practi cally intact or slightl y affected , whereas others are considerably damaged5
. <J. To eva luate the effect of the different enzymatic treatments on the wool surface, SEM s were prepared (some of the most representatives ones are shown in Fig. S). These SEMs also demonstrate that the enzy mes produce different effects on the wool fibre surface.
Enzyme A significantly attacks the wool fibre onl y at hi gher concentrat ions. Some sca le edges are rai sed at the enzyme concentration of 8% (Fig. Sd). The SEMs of wool treated with enzy me B show th at even at the lowest enzy me concentration the wool fibres can be completely desca led (Fig. Se). The bi gges t effect on the sca le structure or on the fibre cortex was produced by a higher cnzyme concentrati on (Figs Sf and Sg). However, the enzy mati c treatment did not produce a uniform effect on woo l (Fi g. Sg ).
As the proteases generall y have a large molecul e, they preferentially attack the hi ghl y swellable cell membrane compl ex (C MC), a non-kerat ini c part of
woo l fibre , by penetrating between cuticular scales. causing sca le stripping and weakening of wool fibreJ
·7
. Moreover, if the CMC is attacked by enzymes it wi ll result in the liberati on of indi vidual corti cal cells2Y
. Since enzyme A leaves the woo l scales int ac t and does not cause excessi ve damage to the \\ 001
(values of we ight loss did not exceed 4.5 0/<) , it could be suggested th at it produces superficia l proteol ys is or kerat inolys is. By contrast, enzy me B removes the surface scales or even liberates indi vidual corti ca l ce ll s at hi gher enzy me conce ntrations. Therefore. it should be strongly controlled or used onl y at lower concentrati ons.
It is well known th at the mechani ca l properti es of wool fibre are closely related to the structure of the ce ll membrane compl ex]()' 31 . Hence, the mechan ical properti es such as tensi Ie strength of wool remain unchanged after any treatment restri cted to the wool surfaceJ2 The ya rn tensi Ie strength was determi ned (Table 4) to confi rm thi s. At th e central point of experimental design, the treatment using enzyme A does not ca use the excess i ve tensi Ic strength drop (2.83%) in contrast to the trea tment with enzy me B (9.62%). Moreover, the tensil e strength drop becomcs progressive as the enzy me concentration is increased regardless of the enzyme used.
The results of FTIR/ATR measurements show that the enzy matically-treated wool ex hibited poor changes in the redox state of -S-S- cyst ine bonds (Fig . 6). The peak intensity of cyst ine monox ide and cys ti ne di ox ide are sl ightl y changed after enzyme treatments. Untreated wool has a certa in amoullt of cystei c acid, probabl y due to weatherin g or photo-
'd . " 34 TI "d I' h I OXI atl on' -. . le cysteic aC I content s Ig t y red uces on increasing the enzyme A concentrati on with respect to the untreated sa mpl e (Fi g. 6a). The cysteic ac id content of enzy me B treated wool also fo ll ows the sa me pattern (Fig. 6b). However, an increase in the er, zy me B concentrati on does not give ri se to significant differences in the cysteic ac id
Tablc 4-Calcul a lcd ya rn lcnsil e slrenglh propenics aflc r enzy mal ic lrealmenls
Enzyme Durali o n o f Enzy me A
cone. lrealme nl Tensile <; lrenglh" Tensi Ie sl rengl h % min cNltex drop. %
I 60 6.94±0.22 1.84
4.5 60 6.87±0. 16 2.83
8 60 6.77±0.12 4.24
(Untrealed) 7.07±0.20
, Errors are indi ca ted al 95 % confidence )eve l.
Enzy me B
Te nsi le stre nglh a
eNltex
6.83±0 .23
6.39±0.16
5.8 1±0.38
7.07±0 .20
Tensi Ie strc ngth drop. %
3.39
9.62
17.82
4 14 INDI AN .I . FIBRE TEXT. RES., DECEMBER 2002
I . ~ ;. I h I t ~. I
I L' I I II
Fi g.5- SEMs of wool: (a) unlrea ted; (b-d) treated for 60 min with 1%, 4.5 % and 8% respectively of enzy me A; and (e-g) Ireated for 60 min with 1%, 4.5 % and 8% respectively o f enl.Yllle B
JOVANCIC el al.: A COMPARATIVE STUDY OF TWO WOOL ENZ YME TREATMENTS 4 15
~ .
0.5 (a) 0.4 1\ 0.2 :~~ / \ p' \ .' A / \
~ .8 V ~.8
-1 .0 ~ Cystlllt.." C YS!.:! IC
-1 .2 . ,: dIoxide a~itl -- Untrc:ltt!d
," - . - . EIl~'lIC r\ Irea h!d. I G~ ~1 . .( . _ _ _ En.rvllIt.! A Irc;IIt.!<L ·1 '\° 0
.. . .. . . . EnzYllIt.!:\ I r~atcd . go 0
!:J U (b)
~ :~ '\ :~ rrfY):0 \ r .(l .S '/ Cystlllc 1II0 11('lXl (h ! i ~ .{l.B J (~ ox i cll!
-1.0 II C)~~d' l eIC --U lltTt.!:l h!<1 ~ . <le i
' 1.2 : i - . - . EI1L)l l1C B tfca l t!ci, 1 °'0
-1.4 I 10-4 I
1200
-- __ EIl7)l l1t: 13 trc .Ll t.!d , <1 .5°'0
. . .. . . .. EII7)l lh! B t r~ .I !t:d . 8°'0
1100 1000 900
Wav":llumbcr (em")
Fig. 6- Second-order derivati ve FTIR/ATR spectra of wool treated for 60 min with (a) enzy me A ; and (b) en zy me B
content of wool. This is probably due to the loss of su lphur-ri ch material at the wool surface even at low enzyme concentrations (Fig. 5e).
Despite smoothening or descaling, onl y sli ght shrink resistance is obtained. It seems that to achi eve a good level of shrink resi stance, it is not on ly necessary to modify the cuticu lar scales but also to generaie anionic groups, espec iall y cyste ic ac id and/or cysteine-S- su lphonate groups, on the wool surfaceU5
.
To confer shrink resistance, an enzyme shou ld be highly spec ific toward the outer sulphur-ri ch cuticular layer, preferably after the wool has been modified to enhance this specific/. Disulphide bond splitting by an oxidative or sulphite pre-treatment of wool 27. 16-3X
makes the wool fibre surface more accessible with the result that the consequent enzymatic attack on the cuticle is selecti ve ly activated. It has been fo und that as a consequence of a combined peroxide-enzyme treatment of wool , the enzyme action could be limited to the wool surface because of its ion ic interac ti on with the new su i phonic groups formed on the wool surface39
.
4 Conclusions Wool treatment with app li ed enzyme fo rmulati ons
exerts a positive influence on whiteness and shrink
resistance, but has a detrimental effect on th e physico-mechanical characteristics o f the woo l whi ch are expressed as weight loss, tensile strength and urea bi sulphite solubility. Wool suffers so me damage owing to the type of enzyme, enz me co ncentrat ion and treatment time. Enzyme A coul d be appli ed all over the experimental zone (enzy me concentration 1-8% and treatment time 15 - 105 min), whereas in the case of enzyme B, the enzy me concentrati on over 5% and treatment time over 60 min should be avoided. FTIR/ATR analysi s confil:ms the absence of significant changes in the redox state of cystin e disulphide bonds after the enzyme treatments used in the study.
The SEMs suggest a clear difference between enzymes A and B with respect to the enzy me proteolytic acti vity on the wool surface as well as in the enzyme attack pathways. Enzy me A leaves the wool sca les intact and does not ca~ se excess ive damage to wool. Thus, thi s enzyme preferentially produces a superficial proteolysis or keratinol ys is. By con trast, enzy me B can attack the non-keratinic parts of woo l fibre structure and shou ld , therefore, be strongly contro lled or used at lower concentrations.
Acknowledgement The authors gratefully acknowledge the finan cial
support from MEC (Spain ) through a post-doctoral fellowship for P.Jovanci6, and the C1CYT (Spain) for funding the MAT 98-0790 Project. They are also thankful to M.Dolcet and lM.Fortuno for their help in ex perimental work and SEM observations respecti vel y.
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( 1993) 2 10. 6 Levene R, Cohen Y & Barkai D. J Soc Dyers Colullr, 11 2
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