Modification of Lignocellulosic Fibers in Oil Palm Empty Fruit Bunches by Autoclave and Alkaline Pretreatments for Potential Use as Ruminant Roughage

Oil palm empty fruit bunches (OPEFB) are abundant lignocellulosic by-products with potential as ruminant feed, but their utilisation is limited by high fiber recalcitrance. This study aimed to evaluate the effect of autoclave treatment combined with alkaline pretreatments on the structural characteristics and fiber composition of OPEFB. Unlike previous studies that largely focused on biological delignification or advanced biomass fractionation, this study directly compared urea- and NaOH-assisted autoclave pretreatments by integrating FTIR, SEM, and Van Soest fiber fraction analyses. The experiment consisted of three treatments: untreated OPEFB (T1), OPEFB treated with autoclave and 3% (w/w) urea (T2), and OPEFB treated with autoclave and 3% (w/w) NaOH (T3). FTIR results showed that NaOH-assisted autoclaving caused the strongest weakening of O–H, C–H, C=O, and C–O–C absorption bands, suggesting partial disruption of functional groups associated with cellulose, hemicellulose, and lignin. SEM observations showed that T3 produced the most severe fiber surface disruption, with rough and fibrillated morphology. Fiber fraction analysis showed that T3 significantly reduced NDF, ADF, hemicellulose, lignin, and cellulose contents compared with T1 and T2 (p < 0.05). In conclusion, 3%(w/w) NaOH-assisted autoclaving was more effective than 3% urea in modifying the lignocellulosic structure of OPEFB and may improve fiber accessibility. However, the substantial reduction in cellulose warrants cautious interpretation. Further evaluation of dry matter recovery, residual alkali, rumen fermentation, digestibility, and animal performance is required to confirm its practical value as a ruminant feed ingredient.