NIR-FT-RAMAN SPECTROSCOPY OF FLAX (LINUM USITATISSIMUM L.) STEMS

Authors: Himmelsbach, David; Akin, Danny

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: The stem of the flax plant is the source of linen fiber that is of commercial importance in Europe and Asia. The growing and processing of flax for fiber is gaining interest in the United States. The buying and selling of flax fiber is currently based on its quality as determined by subjective evaluations conducted by expert graders. Consequently, in the US and world-wide, there is a need for rapid and objective analytical methods to determine the quality of flax fibers so that international trade of this commodity may be conducted objectively. This study represents preliminary work aimed at exploring the possibility of using near-infrared generated Raman signals to provide such an analytical method. As the first step in this work, the Raman spectra of pure chemical compounds, known to be present in flax stems, were used as models to assign those spectral signals in actual flax stems. Specific signals were observed for cellulose, hemicellulose, pectins, aromatics and waxes. Thus, all of the major chemical components in flax stems can be detected by the Raman method. These results indicate that this method has potential for the assessment of flax fiber quality and that quantitative analysis should prove successful.

Technical Abstract: Flax (Linum usitatissimum L.) stem and anatomical parts (bast, bast fibers, core, and cuticle/epidermis) were studied by near-infrared-Fourier transform-Raman (NIR-FT-Raman) spectroscopy to determine if the major chemical components of each could be detected by this method. The Raman spectra of flax stems and anatomical parts were compared to spectra of reference compounds that represent the major chemical components found in flax. The reference compounds included: arabinan, calcium pectate, cellulose, ferulic acid, galactan, glucomannan, lignin, methyl polygalacturonate, polygalacturonic acid, rhamnogalacturonan-I, syringaldehyde, stearyl stearate, trilinolenin, xylan, xyloglucan. Increases in the intensity of vibrations ca. 1095 and 380 cm*-1 in the fibers over those in whole stem, bast and core could be attributed to an increase in cellulose content. An increase in the signals in the region 515-470 cm*-1 over that ca. 380 cm*-1 suggests an increase in hemicellulosic polysaccharides in bast and fibers relative to that observed in stem and core. A weak signal for acidic pectins was detected in the region 860-850 cm*-1 in the bast, cuticle/epidermis, fibers and stem, but was not detectable in the core. Bands arising from aromatic ring stretch ca. 1601 cm*-1, gave the strongest absorbances in cuticle/epidermis, core and stem. Bands from waxes and fatty acid esters were detectable in the cuticle/epidermal tissue but not in other materials. These results indicate that NIR-FT-Raman can detect the major chemical components in flax in situ and provide a simple, rapid and noninvasive assessment of their relative amounts and location within the tissues of the flax plant.