Soya beans and maize : the effect of chemical and physical structure of cell wall polysaccharides on fermentation kinetics

The analysis of the relationship between cell wall composition and fermentation of endosperm cell walls of soya beans and maize was approached from three different angles. Firstly, the fermentation (rate and extent of fermentation, the sugar degradation pattern, and volatile fatty acid production) of soya bean and maize cell walls was analysed, both in situ and in vitro. This analysis revealed that the physical structure of the cell wall (particle size and cell wall thickness) influences cell wall fermentation characteristics, and that cell wall polysaccharides from a single cell wall type can be fermented at different rates. Secondly, isolated cell wall polysaccharide fractions, which had been extracted from soya and maize, and subsequently soya and maize cell walls from which polysaccharide fractions had been extracted, were fermented.The fermentation of extracted pectins from soya cell walls was slower than expected, whereas the fermentation of extracted arabinoxylans from maize was very rapid. The cell wall from which part of the non-cellulosic polysaccharides (pectins for soya and arabinoxylans for maize cell walls) had been extracted, were more fermentable than the original cell wall. The cellulose-rich cell wall fraction that remained after further extraction of polysaccharides was less fermentable than the original cell wall for soya, whereas for maize the cellulose-rich residue was similar in fermentation to the original cell wall.Lastly, the fermentation of cell walls from different plants, within the same plant group (mono- and dicotyledons), were compared with the fermentation of the soya and maize cell wall, so as to detect the effect of differences in carbohydrate composition on cell wall fermentation. For monocotyledons an increase in particle size decreased rate of cell wall fermentation, other clear relationships between cell wall composition and fermentability were not found. For dicotyledons an increase in sugar content, most likely related to a lower in protein content, decreased half-time of gas production. The results are interpreted using the models for the mono-and dicotyledon cell walls, proposed by Hatfield (1993).