Degradability of phenolic acid-hemicellulose esters: A model system

A synthetic model system containing p-coumaric and ferulic acids esterified to hemicellulose was used to study polysaccharide degradability. Oatspelts xylan was fractionated into Alinear, Blinear and Branched fractions prior to synthetic esterification with phenolic acids at treatment concentrations of 0, 25, 50, 75 and 100 g phenolic acid per kg hemicellulose. Concentrations of phenolic acids esterified to the hemicellulose fractions were determined by alkaline hydrolysis. In-vitro dry matter disappearance (IVDMD) and degradability of hemicellulose neutral sugars were measured after 48 h ruminal fermentations. Esterification efficiency of the phenolic acids to the hemicellulose fractions was low (0.3 to 13.9%) and greater for p-coumaric than ferulic acid (4.7 vs 3.1%, respectively). Concentration of esterified phenolic acids was negatively correlated with IVDMD for the Alinear and Bbranched fractions. Ferulic acid appeared to be more inhibitory to IVDMD than p-coumaric acid. Generally the degradability of the side chain sugars of the hemicellulose fractions was negatively correlated with esterified phenolic acid concentrations. Xylose degradation was only correlated with esterified ferulic acid level in the Alinear fraction. The in-vitro ruminal fermentations resulted in the degradation of the majority of the phenolic acid esters. Analysis of the synthetic phenolic acid-hemicellulose esters by 13C NMR and FTIR was unable to prove the presence of monomeric phenolic acid esters. The presence of phenolic acid polyesters was unlikely because of the solubility of the synthetic phenolic acid-hemicellulose esters. The neutral sugar degradation data suggest that esterification of the phenolic acids was limited to sugars with primary hydroxyl groups. While this model system was useful for studying cell wall degradation, future studies must employ model systems in which the chemical constituents being tested accurately model those found in nature.

[1]  D. E. Akin.  Forage Cell Wall Degradation and ρ‐Coumaric, Ferulic, and Sinapic Acids1 , 1982 .

[2]  G. Fahey,et al.  Effects of ruminant digestion and metabolism on phenolic monomers of forages , 1983, British Journal of Nutrition.

[3]  Hansang Jung.  Inhibition of structural carbohydrate fermentation by forage phenolics , 1985 .

[4]  R. Hartley,et al.  Linkage of p-coumaroyl and feruloyl groups to cell-wall polysaccharides of barley straw , 1986 .

[5]  J. Azuma,et al.  Lignin-Carbohydrate Complexes Containing Phenolic Acids Isolated from the Culms of Bamboo , 1985 .

[6]  J. C. Street,et al.  Correlations of Phenolic Acids and Xylose Content of Cell Wall with In Vitro Dry Matter Digestibility of Three Maturing Grasses , 1984 .

[7]  O. Theander,et al.  Studies on dietary fiber. 3. Improved procedures for analysis of dietary fiber , 1986 .

[8]  D. E. Akin,et al.  Effect of forage cell wall phenolic acids and derivatives on rumen microflora , 1989 .

[9]  P. F. Hudrlik,et al.  Survey of organic syntheses , 1970 .

[10]  R. Hartley,et al.  p‐Coumaric and ferulic acid components of cell walls of ryegrass and their relationships with lignin and digestibility , 1972 .

[11]  Hansang Jung,et al.  Forage Lignins and Their Effects on Fiber Digestibility , 1989 .

[12]  S. L. Fales,et al.  Cinnamic acid–carbohydrate esters: An evaluation of a model system† , 1989 .

[13]  Hansang Jung,et al.  Variation in the extractability of esterified p-coumaric and ferulic acids from forage cell walls. , 1990 .

[14]  B. Gaillard.  Comparison of the hemicelluloses from plants belonging to two different plant families , 1965 .

[15]  E. Guittet,et al.  Comparison of Wheat Straw Lignin Preparations - I. Chemical and Spectroscopic Characterizations , 1986 .

[16]  R. W. Bailey,et al.  The distribution of galactose and mannose in the cell-wall polysaccharides of red clover (Trifolium pratense) leaves and stems , 1968 .

[17]  K. Vogel,et al.  Influence of lignin on digestibility of forage cell wall material. , 1986, Journal of animal science.

[18]  Hansang Jung,et al.  Depression of cellulose digestion by esterified cinnamic acids , 1986 .

[19]  Hansang Jung,et al.  Light Source and Nutrient Regime Effects on Fiber Composition and Digestibility of Forages , 1991 .

[20]  J. Azuma,et al.  Lignin-Carbohydrate Complexes and Phenolic Acids in Bagasse , 1984 .