Effect of partial delignification on the in vitro digestibility of cell wall polysaccharides in Digitaria decumbens (pangola grass)

Abstract

Leaf and stem fractions of Digitaria decumbens (pangola grass) cut at two stages of regrowth (47 and 89 days), were extracted with ether, ethanol and water (100°C) before being partially delignified with sodium chlorite in acetic acid. Delignification reduced the lignin concentrations by 52 and 72% in the 47-day-old leaf and stem, and by 69 and 87% in the 87-day-old leaf and stem. In vitro dry matter digestibility was correspondingly increased, by 17–20% (47-day material) and 28–31% (89-day material). Hemicelluloses were digested to a greater degree than cellulose in the delignified material. The reverse was found in the material prior to delignification. In the hemicelluloses arabinose was always digested to a greater extent than xylose. Polysaccharides from delignified 89-day regrowth leaf and stem tissue were still digested to a lesser extent than those from the 47-day regrowth. Maximum digestibilities estimated for zero lignin content were 96.6, 88.1 and 82.8% for young leaf, young stem-told leaf, and old stem respectively. Thus, while lignin has been shown to be the major factor limiting total digestion of the plant material, other minor factors could not be excluded, particularly in the older tissues.