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 extr acted with different chemicals to obtain the cell-wall fraction. Soya bean meal cell walls were incubated in the rumen of a fistulated cow. The indivi dual 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 de graded material revealed the presence of two cell wall types, with distinct ly different degradation characteristics: one originating from the hull (th ick, slowly degraded) and one from the endosperm (thin, rapidly degraded). Furthermore, the cell-wall sugar composition of endosperm and hull cell wal ls was different, most markedly for galactose (281 vs. 12 g kg(-1)) and glu cose (132 vs. 508 g kg(-1)). The degradation of endosperm and hull cell wal ls was measured in vitro by use of in vitro cumulative gas production. Degr adation rates of the individual cell-wall sugars for hull cell walls were s imilar (ranging from 2.4% to 4.6% h(-1)). For endosperm cell walls, the deg radation rates of the individual sugars were different brit with the same r anking 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 degra dation pattern is influenced by the presence of two cell-wall types (hull a nd endosperm cell-wall), which differ in their rate of degradation and suga r composition. The difference in cell-wall sugar degradation pattern betwee n hull and endosperm cell walls is likely to be caused by a combined effect of particle size and cell-wall thickness. (C) 1999 Elsevier Science B.V. A ll rights reserved.