Effect of autoclaving sugar‐beet fibre on its physico‐chemical properties and its in‐vitro degradation by human faecal bacteria

The effect of structure and properties of sugar‐beet fibre on its degradability by human faecal bacteria was investigated by an in‐vitro fermentation test. The composition and physico‐chemical properties of sugar‐beet fibre were changed by autoclaving. Autoclaving at 122°C and 136°C for I h increased the solubility mainly of pectins and arabinans and caused increased swelling. The form of the fibre influenced the water‐binding capacity, the ionic form giving lowest values. Increasing the ionic strength of the medium reduced the water‐binding capacity, especially for the raw fibres and fibres autoclaved at 122°C. The composition of the fibre did not entirely explain these differences and the three‐dimensional arrangement of the different polymers in the cell wall was apparently involved. Galacturonic acid and arabinose were extensively depleted by human faecal bacteria and after 24h more than 80% of the initial carbohydrates had been degraded. However, the time course measurement of residual polysaccharides, production of short‐chain fatty acids and values of pH showed differences in the rate of fermentation; the presence of solubilised material stimulated bacterial proliferation. The removal of pectic polysaccharides increased the degradability of cellulose and this fact suggested that accessibility is mainly responsible for the slow attack of cellulose in sugar‐beet fibre.