Optimizing Feedstock Valorization Through Fungal Co-Fermentation of Thin Stillage and Soybean Hulls

Abstract This study investigates the upcycling of two major agro-industrial by-products, thin stillage (TS) and soybean hulls (SBH), through submerged fungal fermentation (SmF). TS and SBH served as carbohydrate and protein-rich growth medium for filamentous fungi, Aureobasidium pullulans ( Ap ), Aspergillus oryzae ( Ao ), Trichoderma reesei ( Tr ) and Aspergillus niger ( An ), aiming to enrich protein, total phenolic contents (TPC), and antioxidant activity. SmF was conducted using TS alone and TS supplemented with SBH (TS + SBH) as substrates. The results demonstrated that all fungi significantly increased the crude protein (CP) of pellets, and the addition of SBH to TS improved nutrient recovery as well as total solids recovery up to 71.0%. TPC of TS alone, and TS + SBH increased by upto 100.6%, and 57%, respectively, following a 5-day fermentation. This enhancement in TPC correlated with a significant increase in antioxidant activity (4-fold by Tr in TS alone and 1.2-fold by An in TS + SBH). The maximum phytic acid reduction was 43.2%, dependent on the substrate and fungal strains. Ap reduced the total sugars by 69.3% in TS and 48.66% in TS + SBH. This study highlights TS and SBH as effective fermentation feedstocks that enhance nutritional and bioactive properties, supporting sustainable bioethanol production and waste valorization into value-added products. Graphical Abstract