CHARACTERIZATION OF DIGESTION RESIDUES OF ALFALFA AND ORCHARDGRASS LEAVES BY MICROSCOPIC, SPECTROSCOPIC AND CHEMICAL-ANALYSIS

Leaflets of alfalfa (Medicago sativa L) and leaf blade sections of orc hardgrass (Dactylis glomerata L) were digested for three consecutive i ncubation periods of 3 days each with rumen bacteria. Residues were th en analyzed by the following methods: (i) scanning electron and light microscopy to define the botanical structures; (ii) ultraviolet absorp tion microspectrophotometry to characterize phenolic constituents with in specific regions; (iii) NMR and mid-infrared spectroscopy to determ ine components, linkages, and functional groups: and (iv) gas-liquid c hromatography for phenolic acids and lignin constituents after treatme nt with 1 M NaOH (25-degrees-C, 24 h) and 1 M NaOH followed by 4 M NaO H (170-degrees-C, 2 h). Alfalfa residue consisted of extensive amounts of cuticular sheets, a network of vascular bundles. and smaller porti ons of cuticle overlying lignified structures associated with major va scular bundles. Orchardgrass residue consisted of large and small vasc ular bundles, usually without the mestome sheath surrounding phloem. a nd small portions of cuticle. Alfalfa lignin was more condensed but ha d similar proportion of ether-linked phenolic acids compared with that of orchardgrass, while the grass lignin had substantially higher conc entrations of ester-linked p-coumaric and ferulic acids associated wit h a higher proportion of carbohydrates in the residue. Alfalfa had a h igher fatty ester content, likely due to the large amount of cuticle i n the residue, and protein, which likely was contained within the lign in. The results provide a detailed characterization of aromatics and l inkages within the most recalcitrant tissues of plants and indicate va riations between non-degradable residues of a legume and a grass.