Effect of lignin peroxidases obtained from white rot fungi in delignification of cereal crop residues for ruminant feeding: changes in chemical composition and in vitro digestibility

Abstract

Crop residues are renewable sources of energy for ruminants. Pre-digestion of such materials with ligninases from white rot fungi may transform the lignocellulosic substrate into a feed with greater digestibility and higher quality for ruminants. This study has evaluated the effect of crude (T1) and purified(T2) lignin peroxidase (LiP) obtained from immobilized white rot fungi (LPS1) on chemical composition and in vitro digestibility of nine cereal crop residues commonly used for feeding ruminants. Untreated straw served as control(C). Each straw was hand chaffed into 2.3 to 3.0 cm bit length and treated with the enzyme by spraying at a ratio of 1:2.5 and left for 24 h before analysis. Significant P and F values at 99% CI respectively were obtained in case of ADF, NDF and ADL with both T1 and T2. Also in vitro digestibility of dry matter (IVDMD) increased significantly in both T1 and T2. Highest increase of 20 % in IVDMD was obtained upon treatment of BRM, FXM and PRM with purified lignin peroxidase (T2) while LM showed the lowest of 12.34 % . T2 thus showed higher digestibility than T1 for all the crops as shown by LS means. Correlation graph with digestibility on Y-axis and lignin degradation on X-axis showed a strong negative correlation for all the crop residues used with increase in digestibility giving a linear decrease in lignin content or vice versa. Also digestibility and lignin degradation differed for each type of straw evaluated. BRM and LM showed a very strong negative correlation (correlation coefficient r= -98.54 and -98.07) with FXM (r = -92.43) being the next in line followed by FMS (r=-87.67) and BA (r=-87.39). PRM, MS and PS followed with JR (r= -66.54) at the end. High yield of LiP obtained through immobilization on PUF cubes was effective in delignification and could be employed for enhancing the digestibility of crop residues.