The Chemical Composition of Grasses With Particular Reference to the Structural Carbohydrates

Gorrod, Alan Robert Noel (1957) The Chemical Composition of Grasses With Particular Reference to the Structural Carbohydrates. PhD thesis, University of Glasgow.

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The methods of chemical analysis of dried grass have usually included the determination of the ash, ether extract, crude protein and crude fibre. The remainder of the material has been calculated as the nitrogen-free extractives. It was decided to make a more detailed analysis of grasses by the examination of successive extracts, and methods have been developed which allow almost all of the dry matter to be accounted for in terms of the major constituents. The grass samples were examined by the successive use of various neutral extractants and the amount of material removed by each reagent was determined. The weighed, extracted material together with the fibrous residue accounted for 99-101% of the grass dry matter. When the individual extracts and the fibrous residue were further fractionated, the sum of the individual constituent groups amounted to 93-99% of the grass dry matter. Of this total 3-5% was not identified. Unidentified compounds were found in particular in the extracts obtained by the use of water and ammonium oxalate solution. After extraction of the readily soluble components from the grass, the structural constituents were examined in the residue. The protein and lignin were largely removed from the residue by treatment with pepsin and the preparation of chlorite holocellulose. During the examination of the holocellulose, evidence was found to suggest that chloriting had rendered some of the residual lignin alcohol-soluble. The polysaccharides in the holocellulose were studied by successive extraction with water, alkali and acid. The sugars in the hydrolysed extracts were separated by paper chromatography and estimated by periodate oxidation. These methods of analysis of the grass samples were applied to four perennial grasses and one annual grass, each cut at four stages of growth. The amount of the neutral extracts were determined hut not examined in detail since this part of the work was concerned mainly with the changes in the composition and quantity of the fibrous residue. There were only slight differences between the perennial grasses in the amounts of polysaccharides and lignin at corresponding stages of growth. The annual rye-grass contained relatively more lignin, and cellulose represented a greater proportion of the total polysaccharides than in the perennial grasses. These differences may result from the more rapid growth habit of the annual grass. In all the grasses, cellulose represented approximately half the cell wall polysaccharides. The hemicelluloses contained mainly xylan with smaller amounts of araban, glucosan, galactan and uronic anhydride. The quantity of xylan increased markedly with increasing age whereas the amount of the other constituents changed only slightly. Differences in the composition of the structural material of the leaf and stem portions of the grasses were quite small.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Plant sciences, Botany, Range management
Date of Award: 1957
Depositing User: Enlighten Team
Unique ID: glathesis:1957-79242
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 11:25
Last Modified: 05 Mar 2020 11:25

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