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Title: The fermentation of 14C-plant cell walls in the rat gastrointestinal tract
Author: Gray, Douglas Fraser
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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Dietary fibre (DF) has become an increasingly important part of a healthy diet as its fate in the gastrointestinal (G.I.) tract becomes apparent. The heterogeneous nature of DF components makes the understanding of the overall beneficial effects confusing. The methodology has been limited and in this thesis a new approach to investigating the fate of a radioactive dietary fibre marker in the G.I. tract of rats is described. A U-14C-plant cell wall preparation produced from spinach cell cultures was analysed by various chemical and enzymic techniques. The 14C distribution in the plant cell wall was confined mainly to the major polysaccharide groups: pectins (48.4%), hemicelluloses (15.3%), cellulose (21.3%) and starch (2.6%). The pectins consisted of predominantly homogalacturonan and the major hemicellulose was xyloglucan. The analsyis confirmed that the suspension cultured spinach cell walls were a good comparison with other plant cell walls. Therefore the U-14C-plant cell wall preparation was used in animal studies as a marker for dietary fibre and its fate investigated. The pectic fraction of the cell walls was degraded completely in the rat G.I. tract but the hemicellulose/cellulose fraction was still detected in the colon. It is postulated that the chemical and physical properties of different plant cell wall polysaccharides will dictate their fate in the caecum and colon with respect to degradation by the bacterial microflora. The U-14C-plant cell wall preparation was over 85% degraded by the bacterial micorflora and the fermentation products were utilised by the host. The incorporation of 14C into host tissues was high (22% of the 14C dose) as was the production 14CO2 (26% of the 14C dose) in high fibre fed animals. In vitro fermentation, using a caecal inoculum, confirmed the production of short chain fatty acids (SCFAs) with reduced 14CO2 production (12% of 14C dose). These studies show that both bacterial fermentation of 14C-plant cell walls and host metabolism of 14C-SCFAs result in the production of 14CO2. Comparative studies using animals maintained on low fibre diets showed that both the 14CO2 production in vivo (16% of 14C dose) and in vitro (7% of 14C dose) were reduced. The level of SCFAs was also much lower in the low fibre fed animals suggesting that their caecal bacterial capacity to ferment polysaccharide was grossly reduced. By using the ratio of in vitro to in vivo production of 14CO2 as an indicator of the host capacity to absorb and metabolise SCFAs it was clear that there was no difference between a high and low fibre diet, despite the differences between the activities of the bacterial populations. To conclude, these U-14C-labelled spinach cell walls are a good marker to investigate the fate of DF in the G.I. tract. There is a potential to use the methods described to extend the available information on the biological effects of dietary fibre in our diets.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available