Insights into metabolic transformations during solid-state fermentation of copra meal by Aspergillus niger FSPL104 as affected by different nitrogen sources supplementation

Solid-state fermentation has emerged as a promising bioprocessing strategy for enhancing the nutritional value of agricultural by-products. This study investigates the metabolic transformations of copra meal fermented with Aspergillus niger FSPL104 under different nitrogen supplementation conditions. Three treatments were studied: no nitrogen supplementation (T1), ammonium sulfate supplementation (T2), and peptone supplementation (T3). Time-course metabolic profiling and β-mannanase activity analysis revealed that nitrogen supplementation significantly influenced microbial metabolism, enzyme activity, and metabolite production. The highest β-mannanase activity (4.79 U/g) was recorded in T3 after 6 days, followed by T2 (4.39 U/g) and T1 (4.47 U/g). The release of reducing sugars and increased β-mannanase activities during fermentation of nitrogen-supplemented treatments indicate enhanced microbial fiber breakdown. Nitrogen supplementation also upregulated amino acid biosynthesis, particularly in T2 and T3, suggesting enhanced protein metabolism and improved nutrient availability in the fermented substrate. Ammonium sulfate promoted rapid microbial growth and enzyme production, while peptone resulted in a sustained and diverse metabolic response due to its complex composition. In contrast, no nitrogen supplementation limited metabolic flexibility and nutrient transformation. Notably, elevated N-acetylmannosamine levels in nitrogen-supplemented treatments suggest its potential as a biomarker for fermentation dynamics. These findings highlight the critical role of nitrogen sources in optimizing solid-state fermentation processes.