LASER-INDUCED FLUORESCENCE (LIF) SPECTRA OF HERBACEOUS AND WOODY PRE- AND POST-DIGESTED PLANT MATERIAL

Authors: Anderson, Dean; FREDRICKSON, ED - NEW MEXICO STATE UNIV; NACHMAN, P - NEW MEXICO STATE UNIV; Estell, Richard - Rick; Havstad, Kris; MURRAY, LEIGH - NEW MEXICO STATE UNIV

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fluorescence occurs when light with sufficiently high energy is absorbed by a molecule exciting an electron within the molecule to a higher energy state. The subsequent return of the electron to its unexcited state is often accompanied by fluorescence. Twenty dried materials (plants and feces from Angora goats eating some of the plants) having different ages (1 1to 18 years) were examined for laser-induced fluorescence (LIF). The materials were ground and suspended in the solvent chloroform. The filtered solvent was then exposed to light produced by a neodymium:yttrium aluminum garnet laser. The spectral signatures of these materials were examined to determine if the LIF they produced could be used to distinguish among materials. The spectral signatures arising from the 20 materials appeared different. Mean peak fluorescence differed in both wavelength and peak counts across the spectral range between blue and red. Peak fluorescence was evaluated in the blue near 455 nm, in the red near 674 nm and in the green near 528 nm. In general, the blue and green fluorescence peaks were short and broad while the red peak was tall and narrow. Materials differed statistically based on red/blue, red/green and blue/green count ratios. For 16 materials both replicates had peak fluorescence in the blue, green and red regions. Simultaneously analyzing these 3 count ratios in a multivariate analysis indicated 5 materials were quite unique and differed from one another while the remaining 11 materials formed unique sub groups of 2 or more materials. Further research will be required to determine what compounds are producing the spectral signatures and how sample preparation affects LIF.

Technical Abstract: Filtrate from pre-and post-digested plant material was exposed to 355 nm pulsed laser light and the subsequent laser-induced fluorescence (LIF) was recorded. Similarities and differences among spectra from the 20 materials are discussed. Each material was replicated once, dried, ground and exposed to chloroform (CHCl3) for 24 hr. The material represented aged (1 to 18 years old) plants from different herbaceous (grasses and forbs) and woody plant life forms. Mean peak fluorescence recorded among materials differed (P<0.0001) in both wavelength and peak amplitude (counts) across the spectral range (387 nm to 788 nm). Peak fluorescence was evaluated within each of three arbitrary color categories, blue near 455 nm and red near 674 nm while only 16 of the materials produced a green peak near 528 nm. In general, the blue and green fluorescence peaks were broad while the red peak was narrow. Mean peak counts were largest in the red range (1:1328). Varying amounts of laser beam absorption occurred among the materials evaluated due to different concentrations of filtrate and different absorption efficiencies, therefore, amplitude data (counts) were not used to determine statistical differences among materials. To overcome difficulties attributed to the raw count data red/blue, red/green and blue/green count ratios within replicates were calculated. Using all three count ratios in a multi variate analysis of variance, the 16 materials could be separated into nine different (P<0.05) material groupings. The LIF technique may provide a reliable means to separate ground pre- and post-digested plant materials following further research into determining what fluorophores are producing the spectral signatures and how sample preparation affect peak wavelengths.