Journal of the Science of Food and Agriculture J Sci Food Agric 79 :3–10 (1999)

Chemical, microscopic, and instrumentalanalysis of graded flax fibre and yarnWH Morris on III,* DE Akin, DS Himmels bach and GR GambleRB Rus s ell Agricultural Res earch Center, USDA–ARS,Athens , Georgia 30604, USA

Abstract : A series of ýax übre and yarn samples that had been commercially graded low, medium,

and high quality were analysed by light microscopy, wet chemical analysis, Raman spectroscopy, and

nuclear magnetic resonance (NMR) spectroscopy to determine characteristics which could be related

to quality ratings for each sample type. Light microscopy revealed fragments of cuticular and epider-

mal material bound to the übres. As the quality ratings improved, fewer of these fragments were

found and greater separation of the übre bundles to smaller bundles and, in some cases, elementary

übres occurred indicating more efficient retting. Chemical evaluation showed that, as quality of the

yarns increased, amounts of fatty acid and long-chain alcohols as well as dihydroxy fatty acids

decreased. Chemical data on übre did not show consistent trends with quality. Raman spectroscopy

showed increasing amounts of cellulose and decreasing amounts of aromatics and hydrocarbons with

increasing quality, which paralleled the chemical data. NMR analysis showed nearly equal amounts of

crystalline cellulose regardless of quality for both übre and yarn samples. The strengths and weak-

nesses of each analytical method are discussed. This initial study suggested that chemical constituents

characteristic of cutin and waxes could be used as an initial marker of quality.

1999 Society of Chemical Industry(

Keywords: ýax ; quality measurements ; chemical/instrumental evaluations

INTRODUCTION

Flax (Linum usitatissimum L), the source for linen, isa commercially important crop in Europe and isgaining interest in the USA.1 Flax übres are freedfrom the plant by a process called retting. In the pre-dominant retting method, ie dew-retting, the ýaxplant is pulled from the ground and left in the üeldwhere, under proper moisture and temperature con-ditions, indigenous microorganisms degrade pectinsand other matrix polysaccharides. Subsequentmechanical processes, ie scutching and hackling,release bast übres from the stem.

The quality of the ýax übre after dew-retting isdetermined by expert graders and buyers using sub-jective eye and hand evaluations. Quality factors forthe raw übre considered for quality include: weightby hand, strength, üneness, softness, smoothness,pliability, luster, cleanliness, parallelism of strands,freedom from naps and knots, and length and shapeof pieces.2 There are a variety of physical and chemi-cal tests which have been used to characterise übre,3but a clear understanding does not exist to explainhow chemical factors relate to quality. At the presenttime, organoleptic evaluation is much more expe-dient than waiting for chemical evaluation; gradershave individual standards for quality. In contrast,yarn quality is evaluated by instruments thatmeasure characteristics such as strength, elongation,

and evenness. In order to establish standards for thelinen industry, detailed knowledge of the chemistryfor samples graded under current methods is needed.

A better understanding of the chemical character-istics related to quality would help breeders tailorplants to speciüc requirements, aid processors inadjusting retting processes to produce übre of con-sistent quality, and help in the development of on-line, non-destructive techniques to monitorprocessing conditions.

In this study, we determined chemical and struc-tural characteristics of a series of hackled übres andyarns that had been commercially graded as low,medium, or high quality.

MATERIALS AND METHODS

Raw übre, which had been dew-retted, scutched andhackled, and wet spun yarn samples unrelated to theübre samples were supplied by Liniücio & Canapiü-cio Nazionale (Bergamo, Italy). Fibre had been com-mercially graded as (1) ordinary (low), (2) medium,or (3) high quality according to the following subjec-tive criteria: strength, üneness, lustre, colour,length, and shape of sticks. Further, wet spun yarnsamples were graded (1) low, (2) medium, or (3) highquality by the following commercial yarn criteria:strength, elongation, and evenness. Samples were

* Corres pondence to : WH Morris on III, RB Rus s ell AgriculturalRes earch Center, USDA–ARS, Athens , Georgia 30604, USA (Received 19 March 1998; accepted 3 April 1998)

( 1999 Society of Chemical Industry. J Sci Food Agric 0022–5142/99/$17.50 3

WH Morrison III et al

stored in plastic bags until analysed. Fibre sampleswere taken from the centre of the bundle and cut inlengths ranging from 0.5 to 1.0mm. In addition,5-cm long samples were cut from either end ofhackled ýax at a length of 0.5 to 1.0mm. Yarnsamples from the spool were cut to 0.5 to 1.0mmlengths. Samples were treated with 4M NaOH at170¡C for 2h, worked up as previously described,and analysed for phenolics, waxes, and cutin materialby gas–liquid chromatography (GC) analysis of theN,O,bis(trimethylsilyl)triýuoroacetamide (BSTFA)silyl ethers.4 Product identiücation was conductedby GC mass spectrometry (GCMS) on a FinniganGCQ. The column used was a 0.25mm id ] 30mDB-5. Mass spectra were taken at 70eV. Uronicacids were determined by the method of Englyst.5,6Sugars as their alditol acetates were determined by amodiücation of the method described by Hoebler etal.7 All samples were run in duplicate.

Light microscopy

Samples from several regions of the ýax übres andyarns were excised and examined by phase contrastlight microscopy under a 10] objective lens.

Raman spectroscopy

Raman spectra were obtained using a Nicolet 950FT-Raman spectrometer (Nicolet Instrument Cor-poration, Madison, WI, USA) that was equippedwith a notched rejection ülter for 1.064lm and a

beam splitter. The samples used from theCaF2centre of bleached (20 : 1 Clorox) übre to removecoloured particles. Fiber and yarn samples were5–7cm in length, and not cut into smaller sections,with spectra taken along the entire length. Ramanspectra of all samples were collected using 180¡reýective geometry. Samples were positioned in aspring-loaded, vise-style, solid sample holder, andspectra were obtained from an unfocused(collimated) excitation laser beam. Data were col-lected over the Raman shift range of 3006–3990cm~1with a resolution of 16cm~1 over 4K data points,zero-ülled to 8K, and averaged over 256 scans at500mW of laser output power.

All samples were corrected using a white light ref-erence spectrum of KBr. Six replicates were obtainedfor each sample at diþerent positions along the übrelength. Data were collected, Fourier transformedwith Happ-Genzel apodisation, corrected, and therepetitions averaged using Omnic version 3.1(Nicolet Instrument Corp, Madison, WI, USA). Theresulting averaged spectral üles were truncated to therange of 3300–200cm~1, baseline corrected and nor-malised to unit area by dividing each spectrum by itstotal integrated intensity.

Nuclear magnetic resonance spectroscopy

In addition to übre and yarn samples, unretted ýaxübre used in NMR studies, obtained from Van deBilt zaden en vlas Sluiskil (The Netherlands), was

used to illustrate the major resonances of interest.Solid-state 13C cross-polarisation and magic anglespinning (CPMAS) NMR spectra were obtained in aBruker MSL 300 spectrometer tuned to 75.47MHzfor 13C observations. A 4-mm diameter sample rotorspun at 9kHz was used to obtain the spectra with aCPMAS probe. All CPMAS experiments were per-formed using a 2ms contact time, a recycle delay of4 s, and a B1 üeld of 55.5kHz. Spectral widths were30kHz with a 17ms acquisition time, during whichhigh power 1H decoupling was activated. All spectrawere referenced to hexamethylbenzene and were pro-cessed oþ-line using Bayesian/Maximum Entropybaseline corrected, maximum likelihood deconvolu-tion, and maximum likelihood peak ütting using aLorentzian peak width of 0.8ppm.

RESULTS AND DISCUSSION

Light microscopy of low, medium, and high qualityýax übre indicated various degrees of übre separa-tion in all three qualities. However, within the lowquality sample, formidable fragments were foundthat consisted of bundles of übres tightly bound toepidermis and cuticle (Fig 1(a)). Such a structureindicates that the dew-retting process had notresulted in adequate biodegradation of the plantstem,8 leaving the bundles undivided and large plantfragments of übre bundles, epidermis, and cuticle. Incontrast, in the high quality and more efficientlyretted ýax, bundles were subdivided into smallerbundles or even elementary übres, with smaller epi-dermal and cuticle fragments associated with theübres (Fig 1(b) and (c)). However, even in highquality übres, large bundles with attached cuticularfragments were present (Fig 1(b)), although frag-mented bundles with numerous übres often occurred(Fig 1(c)). These micrographs indicate that the shivematerial, originating from the ligniüed core8 wasremoved for the most part and the association of theepidermis/cuticle with übre was a formidable inýu-ence on retting.

Light microscopy of yarns (Fig 2) indicated übrefragments of greatly reduced width compared to theraw übre. In low quality yarn, relatively largebundles were at times present (Fig 2(a)), and frag-ments that appeared to be cuticular in nature wereassociated with the smaller bundles (Fig 2(b)). Inhigh quality yarns, übres and small bundles wereprevalent. However, even in high quality yarns,material that at times appeared to be cuticular, waspresent with the smaller übres (Fig 2(c)).

Treatment of the samples with 4M NaOH cleavesa-aryl and phenolic ethers as well as any esters. Thistreatment has been used to determine the amounts ofguaiacyl and syringyl lignins in plant cell wallmaterial, and results correlate well with Klasonlignin.4 In both übre and yarn samples of ýax, aro-matic compounds are present in very small amountsand in the samples studied were found in only traceamounts.8

4 J Sci Food Agric 79 :3–10 (1999)

Analysis of graded ýax übre and yarn

Figure 1. Phas e contract micrograph of flax fibre. (a) Low quality

fibre s howing fibre bundles (B) s till attached to epidermis and

cuticle (C), forming a large and poorly retted fragment. (b) High

quality fibre with elementary fibres becoming s eparated in

bundles (B) and not as tightly bound with the res idual epidermis

and cuticle (C). (c) High quality fibre s howing bundle (B) with

s eparating elementary fibres (arrow). BarÈ100 lm.

The principle hydrolysis products of the cutin andwax components were long-chain fatty acid alcoholsand acids (Table 1). Of the nine products identiüed,hexadecanoic (no 1 wax) and 8,16-dihydroxyhexade-canoic acids (no 1 cutin) and octacosanol (no 6 wax)accounted for 75–87% of the products identiüed.

Figure 2. Phas e contras t micrograph of flax yarn s amples . (a)

Low quality yarn s howing a moderately intact bundle (B), but with

s eparating fibres . (b) Low quality yarn s howing s maller bundles

of fibres within the yarn, s ome with large bundles (B). (c) High

quality yarn with will-s eparated, s mall bundles and apparent

res idues of cuticle (arrow). BarÈ100 lm.

Amounts of fatty acids and alcohols were lower(P \ 0.05) in the high quality übre and high-qualityyarn compared with the low or medium qualitymaterial. The three dihydroxy fatty acids wereassociated with cutin,9 which make up the outer,protection barrier of the übre or stem, and the

J Sci Food Agric 79 :3–10 (1999) 5

WH Morrison III et al

Table 1. Wax and cutin components in commercial flax fibre and yarn of various qualities components (g kgÉ1)a

Cutinb Total

cutin and

1 2 3 Total wax

Fibre quality

Low 13.7^ 3.5 1.03^ 0.22 0.53^ 0.03 15.3^ 3.3a 26.7^ 1.8aMedium 5.1^ 1.7 0.81^ 0.03 0.47^ 0.2 6.3^ 1.3b 21.5^ 1.6bHigh 12.0^ 0.5 1.2^ 0.03 0.66^ 0.08 14.1^ 0.06a 20.7^ 0.7b

Yarn quality

Low 8.46^ 0.2a 0.79^ 0.03a 0.62^ 0.3 9.9^ 0.6a 14.4^ 1.1aMedium 5.52^ 1.0b 0.41^ 0.01b 0.14^ 0.06 6.1^ 1.0b 7.2^ 0.9bHigh 3.0^ 0.2c 0.35^ 0.04b 0.30^ 0.3 3.7^ 0.05c 4.2^ 0.4c

Wax c Total

cutin and

1 2 3 4 5 6 Total wax

Fibre quality

Low 3.33^ 0.35a 0.86^ 0.35 1.40^ 1.4 1.73^ 0.5 0.39^ 0.3 3.75^ 0.5a 11.5^ 1.5ab 26.7^ 1.8aMedium 7.54^ 1.4b 0.56^ 0.2 0.81^ 0.4 0.99^ 0.1 0.36^ 0.08 4.95^ 0.5a 15.21^ 0.8a 21.5^ 1.6bHigh 2.52^ 0.4a 0.49^ 0.04 0.69^ 0.1 0.84^ 0.6 0.49^ 0.16 1.87^ 0.4b 6.9^ 0.2b 20.7^ 0.7b

Yarn quality

Low 2.47^ 0.2a 0.23^ 0.02a 0.40^ 0.26 0.22^ 0.07a 0.14^ 0.04a 1.08^ 0.04a 4.5^ 0.5a 14.4^ 1.1aMedium 0.61^ 0.08b 0.08^ 0.01b 0.11^ 0.01 0.10^ 0.04ab 0.05^ 0.01b 0.17^ 0.04b 1.1^ 0.1b 7.2^ 0.9bHigh 0.40^ 0.1c 0.02^ 0.01c 0.04^ 0.01 0.02^ 0.0b 0.02^ 0.01b 0.06^ 0.0b 0.6^ 0.1b 4.2^ 0.4c

a Average and s tandard deviation of duplicate analys es . Values within columns within qualities with different letters differ at PO 0.05.b Cutin : 1 – 8,16-dihydroxyhexadecanoic acid, 2 – 9,17-dihydroxyheptadecanoic acid, 3 – 10,18-dihydroxyoctadecanoic acid.

c Waxes : 1 – C-16 fatty acid, 2 – C-22 fatty acid, 3 – C-24 fatty acid, 4 – C-24 fatty acid, 4 – C-26 alcohol, 5 – C-26 fatty acid, 6 – C-28 alcohol.

amounts present were variable with quality of theübre but decreased as the quality of the yarnincreased. The 8,16-dihydroxyhexadecanoic acid (no1 cutin) is by far the most abundant constituent in allsamples, ranging from 5 to 13mg g~1 in the übre and3 to 8mg g~1 in the yarn. In the yarn there was aninverse relationship with the total of the three fattyacids, and particularly with 8,16-dihydroxyhexadeca-noic acid, with the poor quality having the greatestconcentration. This compound could possibly beused as a marker for quality in yarns, but furtherwork is needed on übre samples to address discrep-ancies in the relationships to quality. In general,straight chain fatty acids and alcohols are associatedwith waxes on the outer part of the plant. Total waxcontent (Table 1) was larger in the low quality übrewith a concentration of 11.5mg g~1 compared to6.9mg g~1 for the high quality, but the mediumquality übre did not follow this pattern having a highvalue of 15.2mg g~1. The only compounds with sig-

niücant diþerences in either cutin and wax betweensamples of übre were not clearly related to quality.This indicates a less clear relationship between sub-jective quality evaluation used for the übres andchemical/instrumental evaluations. In the yarn, totalwax values were 4.5, 1.1, and 0.6mg g~1 for low,medium, and high quality, respectively. The totalamounts of materials accounting for wax plus cutinranged from 26.7 to 20.6mg g~1 in the übre and 14.4to 4.2mg g~1 in the yarn, with higher quality übresand yarns having less (P \ 0.05) of these com-pounds. Yarn is bleached to remove coloured impu-rities and is also treated with sodium hydroxide. Thealkali treatment would be expected to remove cuticu-lar waxes, which could aþect dyeing characteristics.A value of less than 0.3% is needed for good dyeingof fabric,10 and both the medium and high yarnsmeet this criteria.

The results of carbohydrate analysis are shown inTable 2. Glucose, representing primarily the cellu-

Table 2. Carbohydrates in flax of various qualities (Linificio)

Carbohydrate components a

Uronic acids Rhamanos e Arabinos e Xylos e Mannos e Galactos e Glucos e

(%) (mggÉ1) (mggÉ1) (mggÉ1) (mggÉ1) (mggÉ1) (mggÉ1)

Fibre quality

Low 3.29^ 0.0a 14.8^ 5.8 9.6^ 4.9 17.2^ 9.1 31.8^ 1.6a 30.2^ 0.7a 563.0^ 2.8aMedium 2.81^ 0.01b 11.2^ 1.4 6.7^ 2.2 9.9^ 1.2 39.9^ 0.6b 26.6^ 2.5a 626.5^ 12.0bHigh 3.10^ 0.09a 11.9^ 1.3 10.9^ 2.9 12.4^ 1.2 45.0^ 0.1c 36.9^ 2.3b 719.5^ 4.9c

Yarn quality

Low 1.63^ 0.08 9.2^ 0.4 4.9^ 1.1a 12.8^ 1.3a 45.6^ 9.5 24.0^ 0.8 692.5^ 95.5Medium 1.42^ 0.0 13.3^ 0.0 5.5^ 0.6a 12.2^ 1.1a 41.5^ 3.7 28.4^ 0.7 756.0^ 19.8High 1.57^ 0.02 17.4^ 3.7 7.9^ 0.3b 22.0^ 0.5b 44.0^ 0.7 28.1^ 1.8 768.0^ 42.4

a Averages and s tandard deviations of duplicate analys es . Values within columns within qualities with different letters differ at PO 0.05.

6 J Sci Food Agric 79 :3–10 (1999)

Analysis of graded ýax übre and yarn

lose in übres, showed signiücant diþerences associ-ated with quality in the übre, with the low qualityübre having the lowest glucose content. Two othersugars showing signiücant diþerences were mannoseand galactose, both at greater levels in the highquality übre. Gorshkova et al11 (1994) have shownthat galacto- and gluco-mannans are components ofýax übres and our earlier studies indicate that galac-tose and mannose follow the same trends as glucoseafter retting.8 In the yarn, there was no signiücantdiþerence in glucose, mannose, or galactose contentwith quality. However, arabinose and xyloseexhibited signiücantly higher concentrations in thehigh quality yarn than in either low or mediumquality yarn. It has been shown that completeremoval of hemicellulose as well as pectin withboiling 6% NaOH causes disintegration of the übrebundles to elementary übres.12 Therefore, a certainamount of hemicellulose appears to be needed tomaintain übre strength.13

Uronic acids (Table 3) were low in concentrationin both yarn and übres. Essentially no diþerencesoccurred with quality in either übre after retting oryarns after processing. These results suggest thatremoval of pectins was uniform regardless of übre oryarn quality and did not appear to be a useful valuefor quality.

Earlier work on ýax8 showed that lignin content inthe übre was small and occurred mainly in the cellcorner and middle lamellae. The amounts remainingafter retting were too small for detection.8 Similarly,in the samples studied here, retting eþectivelyremoved lignin for all übre qualities (not shown).

The solid-state 13C NMR spectrum of unrettedýax bast tissue is shown in Fig 3 to illustrate theprominent peaks of interest. The set of three peaksbetween d 92.0 and 87.0 is assigned as the C-4 ofcrystalline cellulose. The peak centred at d 32.8 isassigned to the groups of epidermal wax,wCH2wand the peak centered at d 21.4 is assigned to the CH3in the acetyl group. All of the remaining peaks in thespectrum are overlapping bands arising from crys-talline and amorphous cellulose, hemicellulose andpectin. The three sets of assigned peaks were interestedas a percentage of the total spectral intensity for theunretted sample, low and high quality retted Ðbre

samples, and the low and high quality yarn samples(Table 3). Though the integrated intensities of thesepeaks did not provide information on the absolutepercentage of the components to which they areassigned and not as deÐned as gas chromatographicanalysis, ratios of the peaks to the total intensity andto each other provide information on the relativeamounts of these components as a function of sample.The results indicated that the low and high qualityretted Ðbres as well as the low and high quality yarncomprised nearly equal percentages of crystalline cel-lulose while, in contrast, the percentage in unrettedÐbres was lower. The retted Ðbres contained less thanhalf the amounts of acetyl groups as the unrettedÐbres, while the yarns showed no acetyl groups as theywould be hydrolysed in the scouring process withalkali. These acetyl groups, which are most likelyattached to the hemicelluloses and generally indicativeof their relative amounts, were similar for both qualityÐbres thus agreeing with GC data on hemicellulosicsugars (Table 2). For the wax component, the lowquality Ðbre and yarn had higher percentages thanhigh quality Ðbre or yarn, respectively. Further, yarnswere much reduced in wax content compared to Ðbres.These resuls are in agreement with chemical, Raman,and microscopic evaluations which show both hemi-cellulose and wax present in the high quality yarn.However, this approach may not be sensitive enoughto measure the small amounts of wax present in thehigh quality samples.

Figure 4 shows Raman spectral plots for the variousquality Ðbres and the results of the spectral subtrac-tion (dashed line) of low from high quality Ðbre. Theoriginal spectra appears similar for all three qualityÐbres, but the di†erence spectrum (1 : 1 subtractionmultiplied 10 times) enhances the di†erences. Thecomponents that were in greater amounts in the highquality Ðbre appeared as positive signals and thosethat were greater amounts in the low quality Ðbreappeared as negative signals. The positive signals thatappear at 1121, 1099, and 386 cm~1 are strong diag-nostic signals for cellulose,14 and thus indicate thatgreater amounts of cellulose occur in the high qualityÐbres. The negative signals that appear at 2885, 1443,and 1296 cm~1 are indicative of greater amounts oflong-chain hydrocarbons,15 which occur in wax and

% Area of s pectral region (contributing groups )

d 92.0–87.0 d 34.0–31.0 d 23.0–20.0(Crys talline cellulos e) (Wax wCH

2w) (Rhamnos e C-6)

Unretted fibre 8.04^ 0.10 1.93^ 0.01 1.05^ 0.10Retted fibre

Low quality 9.09^ 0.1 0.64^ 0.1 0.36^ 0.1High quality 9.19^ 0.01 0.55^ 0.01 0.046^ 0.01

Yarn

Low quality 9.34^ 0.1 0.18^ 0.01 Èa

High quaity 9.20^ 0.1 È È

a Not pres ent.

Table 3. Area percentages of

s olid-s tate 13C NMR s pectral

regions repres enting chemical

groups indicative of flax fibre

components

J Sci Food Agric 79 :3–10 (1999) 7

WH Morrison III et al

Figure 3. Solid-s tate 13C NMR s pectrum of unretted flax

bas t tis s ue.

cutin of low quality Ðbres. The small signal c1600 cm~1 is indicative of greater amounts of aro-matics (lignin or other phenolics) in the low qualityÐbres.16 These results are consistent with the GC datashown in Table 2 for the carbohydrate analyses thatreveals the highest glucose content in the high qualityÐbres. They are also consistent with the GC data for

fatty acids and alcohols analysis in Table 1 that revealthat the low quality Ðbres have the greatest amountsof cutin and wax.

Figure 5 shows that comparable Raman spectralplots for yarns. The positive signals at 1122 and1097 cm~1 indicate that there are greater amounts ofcrystalline cellulose in the high quality material. In

Figure 4. NIR-FT-Raman s pectra of dew

retted flax fibre : high quality (ÈÈÈ),medium quality (– – – –), low quality

(· · · · · · ·) and difference s pectrum of high

minus low (È · ·È).

8 J Sci Food Agric 79 :3–10 (1999)

Analysis of graded ýax übre and yarn

Figure 5. NIR-FT-Raman s pectra of flax

yarn: high quality (ÈÈÈ), mediumquality (– – – –), low quality (· · · · · · ·)

and difference s pectrum of high minus

low (È · ·È).

addition, the negative signal at 1600 cm~1 suggeststhat aromatics are in greater amounts in the lowquality material and are consistent with the GC data.The di†erences in the amount of wax and cutin arealmost undetectable in the di†erence spectrum, but thenegative signals at 2851, 1442, and 1304 cm~1 suggestless cutin and wax in the high quality yarn. It is likelythat the strong increase in signal for cellulose maskedsome of the signals for long-chain hydrocarbons. Thenegative signal between 600 and 400 cm~1 seemed toindicate that there is less hemicellulosic-type carbo-hydrate in the high quality yarn and, in this regard,conÑicts with the GC results. For example, a strongsignal has been observed in b-(1 ] 4) xylan at494 cm~1.17 However, some of the signal di†erenceover this region may be due to the inability to accu-rately adjust the baseline of the spectra in this region.

Total agreement did not occur among the variousanalytical methods. However, generally, the resultsindicated that amounts of dihydroxyfatty acids (cutin)and long-chain fatty acids and alcohols (wax) wereinversely related to quality ratings in Ðbre and yarn.These results were apparent by wet chemical analysesand Raman spectroscopy and agreed with lightmicroscopy showing large fragments of cuticle/epidermis and Ðbre in low quality Ðbre. A certainamount of hemicellulose appears to be necessary formaintaining Ðbre strength. Di†erences in cellulosecrystalline structure are more easily seen in the di†er-ence Raman spectra and point to di†erences in com-position that could be important as a measure of Ðbreand yarn quality.

CONCLUSIONS

Objective standards are required to better assess thequality of ýax. In the search for chemical markers aswell as quick, straightforward, and accurate methods

to develop such standards, we have used a variety ofmethods for a series of both übre and yarn sampleswith diþerent quality using current industry prac-tices. The inverse relationship of cutin and wax con-stituents to quality suggested a possible marker thatshould be tested in further samples. The chemicalmethods for these constituents were conürmed bylight microscopy showing large fragments ofepidermis/cuticle associated with übres especiallyprevalent in low quality samples. Cellulose could alsoprovide a marker since high quality samples con-tained more crystalline cellulose, but the relationshipof other carbohydrates was less clear. With adequateremoval of shives, amounts of lignin or aromaticswere insufficient to provide a marker for quality.These relationships were more evident with yarnthan übre suggesting a clearer relationship betweennon-objective methods used for yarn grading andchemical/instrumental evaluations.

Each of the methods used for analysis have advan-tages and disadvantages. Wet chemical analysis pro-vided the most detailed information but is timeconsuming, destructive, and does not lend itself toon-line use. Light microscopy also is a time consum-ing method but provides structural information onthe condition of the übres and particulate matterwhich may be attached. Raman spectroscopy is arapid method of evaluation which provides generalinformation on the chemical constituents, and agreeswith wet chemical data but, thus far, this methodonly provides semi-quantitative information. It isparticularly sensitive to the presence of aromatics.However, the übre must be nearly colourless as thewavelength and intensity of light used could causecoloured material to ignite. NMR analysis is non-destructive, but is not a rapid method and often notsensitive enough for small quantities. NMR does

J Sci Food Agric 79 :3–10 (1999) 9

WH Morrison III et al

provide useful information on the amount of crys-talline and non-crystalline cellulose, which was notavailable from the other methods. It appears that thebest approach is to use all the mehods to developinformation that might lead to a more efficientmethod of relating physical and/or chemical methodsto ýax übre and yarn quality.

These preliminary results introduced appropriatecompounds and techniques that require evaluation inadditional test samples. Further research is needed toidentify speciüc chemical markers and optimalmethods of measurement related to quality. Thepresent work suggest that wax and cutin constituentscould provide the markers quality for evaluation ofprocessing conditions and how these markers mightbe aþected by verietal diþerences and diþerences inagronomic practices.

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