Fermentation characteristics of cell-wall sugars from soya bean meal, and from separated endosperm and hulls of soya beans

Two experiments were conducted to investigate the degradation of cell-wall sugars from soya bean meal (in situ), and soya bean endosperm and hulls (in vitro). Soya bean meal, soya bean endosperm, and soya bean hulls were extracted with different chemicals to obtain the cell-wall fraction. Soya bean meal cell walls were incubated in the rumen of a fistulated cow. The individual cell-wall sugars were degraded at different rates: galactose (13.6% h−1), arabinose (7.8% h−1), uronic acids (5.1% h−1), xylose (3.5% h−1) and glucose (3.2% h−1). Microscopic evaluation of the cell walls and degraded material revealed the presence of two cell wall types, with distinctly different degradation characteristics: one originating from the hull (thick, slowly degraded) and one from the endosperm (thin, rapidly degraded). Furthermore, the cell-wall sugar composition of endosperm and hull cell walls was different, most markedly for galactose (281 vs. 12 g kg−1) and glucose (132 vs. 508 g kg−1). The degradation of endosperm and hull cell walls was measured in vitro by use of in vitro cumulative gas production. Degradation rates of the individual cell-wall sugars for hull cell walls were similar (ranging from 2.4% to 4.6% h−1). For endosperm cell walls, the degradation rates of the individual sugars were different but with the same ranking as in the in situ experiment (ranging from 20.9% to 7.0% h−1). It was concluded that for soya bean meal cell walls, the cell-wall sugar degradation pattern is influenced by the presence of two cell-wall types (hull and endosperm cell-wall), which differ in their rate of degradation and sugar composition. The difference in cell-wall sugar degradation pattern between hull and endosperm cell walls is likely to be caused by a combined effect of particle size and cell-wall thickness.