Fermentation of Lignocellulosic Substrates Enhances the Safety and Nutritional Quality of Flake Soil for Rhinoceros Beetle Rearing

The rhinoceros beetle (<i>Xylotrupes gideon</i>) requires safe and nutritious flake soil substrate for commercial rearing in northern Thailand, yet optimal lignocellulosic formulations remain undefined. This study evaluated five flake soil formulations substituting lignin-rich cadamba sawdust (0-100%) with cellulose-rich corn stover, plus cattle manure and rice bran, fermented for 90 days. Fermentation engineered the cellulose-lignin-hemicellulose matrix, reducing lignin from 25.07% to 7.30% while enriching cellulose from 29.73% to 33.83% and hemicellulose from 6.67% to 17.42%. Increasing corn stover enhanced crude protein (5.46-7.53%) and nitrogen-free extract (24.17-34.14%), creating T1 (25% substitution) as the optimal cellulose-based composite for <i>X. gideon</i> rearing. Microbial analysis showed T1-T2 supported highest α-diversity and lactic acid bacteria enrichment, suppressing pathogens like <i>Escherichia coli</i> and <i>Salmonella enterica</i>. Fermentation degraded >99% glyphosate residues (from 106 mg/kg to <0.25 mg/kg or undetectable). T1 is recommended as the optimal, sustainable flake soil for <i>X. gideon</i> rearing, balancing nutrition, microbiology, and safety while valorizing agricultural wastes.