LIGNIN IMPACT ON FIBER DEGRADATION .2. A MODEL STUDY USING CELLULOSICHYDROGELS

The impact of lignin on cellulose degradation was studied in vitro usi ng lignocellulosic hydrogels. Hardwood lignin (methoxyl content, 191 m g g(-1)) was blended with cellulose in homogeneous phase solution (dim ethylacetamide/LiCl solvent) in two concentrations (100 and 300 mg g(- 1)) and formed into lignocellulosic beads by dropwise addition of the lignocellulose solutions to an appropriate nonsolvent. The lignin was used before and after hydroxypropylation of the phenolic hydroxyl grou p. cellulose degradation from these beads after 24 and 72 h incubation in buffered ruminal fluid was compared to that of control (cellulose) beads and to that of cellulose beads incubated in the presence of lig nin. The rate of cellulose degradation from the hydrogels was low (12- 16% degradation after 24 h). At 72 h, 21-50% of the cellulose was degr aded. Cellulose degradation was enhanced (P < 0.01) by lignin blended into the beads, but depressed (P < 0.01) by lignin added to the incuba tion medium. The effect of lignin increased (P < 0.001) with lignin co ncentration. Hydroxypropylation of lignin, which blocks the formation of quinone methide intermediates, enhanced (P < 0.001) the increase in cellulose degradation with lignin blending, and reduced (P < 0.001) t he inhibitory effect of lignin included in the incubation medium.