PEER-REVIEWED ARTICLE bioresources.com Majeed et al. (2021). “Lignin-starch biocomposites,” BioResources 16(1), 1940-1948. 1940 Reduction in Lignin Peroxidase Activity Revealed by Effects of Lignin Content in Urea Crosslinked Starch under Aerobic Biodegradation in Soil Zahid Majeed, a,b * Zainab Ajab, c Qingjie Guan, c Abdul Zahir Abbasi, a Qaisar Mahmood, d Mater H. Mahnashi, e Bandar A. A. Alyami, e Ali O. Alqarni, e Yahya S. Alqahtani, e and Nurlidia Mansor b This study characterized the lignin peroxidase (LiP) activity of soil via an enzyme assay to determine the reaction rates and activation energies for 5 wt%, 10 wt%, 15 wt%, and 20 wt% lignin loads in urea crosslinked starch biocomposites. The results revealed that a mixed mode of LiP inhibition occurred after the soil was mixed with these biocomposites with different loads of lignin. Loading of lignin at 5 wt% and 10 wt% lignin resulted in higher values of catalytic activity of LiP: -39.58 and 49.14 μM h -1 g -1 soil, respectively. In comparison, with higher loading of lignin at 15 wt% and 20 wt%, decreases in the catalytic activity of LiP were found and were 28.72 to 37.25 μM h -1 g -1 soil, respectively. The activation energy of LiP increased approximately 1.11- to 1.22-fold when 15 and 20 wt% of lignin was loaded in biocomposites. Research findings established the possibility of unfavorable binding of the LiP to lignin with an increase in the load of lignin, possibly due to the complex structure of intact lignin and presence of inhibitory biodegradation products of lignin accumulates during lignin biodegradation in biocomposites. It was concluded that higher lignin contents (15 wt% and 20 wt%) were effective in reducing the activity of the soil LiP. Hence, higher lignin content possibly protects against losses of lignin, while acting as a filler in the formulation of biocomposites. Keywords: Activation energy; Biocomposites; Lignin peroxidase; Lignin; Michaelis-Menten; Urea crosslinked starch Contact information: a: Department of Biotechnology, University of Azad Jammu and Kashmir, Chehla Campus, Muzaffarabad, Azad Kashmir Pakistan; b: Chemical Engineering Department, Universiti Teknologi PETRONAS, Seri Iskandar, Tronoh, Malaysia; c: Key Laboratory of Saline-alkali Vegetation Ecology Restoration, College of Life Science, Northeast Forestry University, No.26 Hexing Road Xiangfang District, Harbin 150040 P.R. China; d: Department of Environmental Sciences, COMSATS University Islamabad, Abbottabad Campus, Pakistan; e: Department of Pharmaceutical Chemistry, College of Pharmacy, Najran University, Najran 61441 Saudi Arabia; * Corresponding author: zahidfdb@gmail.com; zahid.majeed@ajku.edu.pk INTRODUCTION Lignin is made up of three phenylpropane units, which are syringyl, guaiacyl, and p-hydroxyphenyl. These units build up the complex aromatic structure of the lignin, which has an important role in maintaining the integrity of plant’s cell wall. Lignin also is known to provide protection to plants against pathogens. Lignin peroxidase (LiP) is the first enzyme that has ligninolytic activity, and it was purified from a fungal species, Phanerochaete chrysosporium.