Effect of Fermentation Temperature on Volatile Fatty Acid Production and Fungal Community Structure from Brewer's Spent Grain
Brewer's spent grain (BSG), a major byproduct of the brewing industry, is produced in large quantities globally, yet its high-value utilization remains limited. This study investigated the effects of fermentation temperature (35, 40, 45, 50, and 55 °C) on volatile fatty acid (VFA) production and fungal community structure during anaerobic fermentation of BSG. Results showed that mesophilic temperatures significantly enhanced VFA yields, with the highest production at 35 °C, reaching 344.22 mg/g COD converted, and a peak VFA concentration of 14,267 mg/L after 5 days. Acetic acid dominated the VFA profile (95.6%–98.9%) across all temperatures. Protein and carbohydrate degradation rates were highest under mesophilic conditions, while lipid degradation peaked at 55 °C. Fungal community analysis revealed that at peak acid production, cellulose-degrading fungi were predominant, with Oligophagozyma being the dominant genus at 35 °C (90.07%) and 40 °C (55.31%). Higher temperatures increased fungal diversity and evenness. Mantel tests indicated that carbohydrates and lipids promoted fungal growth, whereas total dissolved solids, nitrate, and phosphate inhibited it. These findings provide insights into the role of fungi in VFA production from BSG and support its resource utilization.