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Separation, Identification and Quantification of Lignin Saponification Products Extracted from Digitgrass and their Relation to Forage Quality¹

University of Florida Gainesville 32611

Abstract

Laboratory analyses were conducted on four digitgrass (Digitaria sp.) hays (2, 4, 6 and 8 wk regrowths) of known voluntary intake and nutrient digestibility. Cell walls were treated with NaOH, and the saponification products extracted were separated and identified by gas-liquid chromatography. The principal phenolic compounds present in the extract were p-coumaric acid (PCA) and ferulic acid (FA). Separation and quantification of the phenolic acids were performed with 3% dimethyl silicone (SE-30) used in a liquid phase, and temperature programming from 100 to 200 C. Extraction time, NaOH concentration and particle size did not affect the yield of PCA and only particle size had an effect (P<.02) on the yield of FA. Repeated measurements of PCA and FA resulted in .93 and .76 intraclass correlations, respectively. Changes in the percentage of FA in neutral detergent fiber (NDF) from 2 to 8 wk (.27 to .3 5%) were small compared to changes in PCA during the same period (.24 to .61%). Organic matter (OM) intake and digestibility declined with advancing maturity. OM digestibility was closely related to NDF digestibility (r = .98, P<.0001). A sharp decline in OM digestibility from 2 to 4 wk (71.9 to 61.4%) was accompanied by increases in permanganate lignin, NDF, acid detergent fiber and PCA. All chemical fractions analyzed were correlated (P<.0001) with digestible OM intake, but the two highest coefficients obtained were for crude protein (r = .96) and PCA (r = -.96).

Key Words: Lignin • p-Coumaric Acid • Ferulic Acid • Forage • Quality • Composition

¹ Florida Agr. Exp. Sta. Journal Ser. No. 2959.

² Graduate student, Dept. of Anim. Sci.; present address: Facultad de Agronomia, Universidad de Costa Rica, San Pedro, San Jose, Costa Rica.

³ Dept. of Anim. Sci.

⁴ Dept. of Food Sci. and Human Nutr.

⁵ Dept. of Agron.