INVITRO DISAPPEARANCE OF CARBOHYDRATES, PHENOLIC-ACIDS, AND LIGNIN FROM PARENCHYMA AND SCLERENCHYMA CELL-WALLS ISOLATED FROM COCKSFOOT

Insight into the structure and digestion of the cell-wall matrix may be gained by studying the in-vitro disappearance (IVD) of constituents from cell types which are contained in forage fibre. The objective of this study was to determine the IVD of neutral sugars, uronic acids, esterified phenolic acids, and lignin from parenchyma and sclerenchyma walls isolated from the plant parts of cocksfoot (Dactylis glomerata L). Cell walls were incubated in a rumen fluid-buffer medium for 0, 12 or 96 h. The chemical composition, apparent digestion and IVD of constituents varied considerably within and between cell types. Parenchyma had higher arabinose to xylose and ferulic acid to p-coumaric acid ratios and lower lignin concentrations than sclerenchyma. The apparent digestion of parenchyma was 240% greater at 12 h and 20% greater at 96 h than that of sclerenchyma. The IVD of cell-wall constituents from parenchyma ranged from 12 to 80% at 12 h and 46 to 99% at 96 h. The IVD of constituents from sclerenchyma was lower than that from parenchyma, ranging from 5 to 50% at 12 h and 47 to 89% at 96 h. Across all cell types, IVD was usually greatest for ferulic acid and lowest for lignin. These findings indicate that the differential loss of constituents from fibre is due in part to differential loss of constituents from both fast and slowly digested cell types. Ferulic acid was the most uniformly removed constituent across cell types. This suggests that ferulic acid is associated with regions of the cell-wall matrix which change little between cell types relative to structural carbohydrates and other lignins.