Fungal biocatalytic valorization of sorghum: an integrated bottom-up and top-down framework for sustainable fermentable sugar production

Fungal biocatalytic valorization of sorghum: an integrated bottom-up and top-down framework for sustainable fermentable sugar production

This study presents an innovative research and optimization framework for maximizing fermentable sugar production from sorghum without any commercial media and chemical pre-treatment. It utilizes bottom-up and top-down approaches to establish a cost-effective and environmentally sustainable sorghum-based biorefinery. Leveraging the biocatalytic potential of Aspergillus awamori and Aspergillus oryzae, solid-state fermentation (SSF) and submerged fermentation (SmF) processes enhanced sugar yield. SSF emerged as the superior fermentation strategy, yielding an unprecedented total reducing sugar (TRS) concentration of 304.83 g/L (609.74 mg/g, db) from sorghum grain (particle size 1.18–0.6 mm) using A. awamori at 60 °C after 72 h of saccharification, achieving a saccharification efficiency of 83.17%. Optimized particle sizes of grain (1.18–0.6 mm) and bran (<0.6–0.3 mm) facilitated maximum TRS (304.83 g/L), α-amylase (982.5 ± 7.45 U/g), glucoamylase (10.93 ± 0.58 U/mL), and protease (168.05 ± 4.35 U/g, dry basis) production using A. awamori under solid-state fermentation. Notably, increasing saccharification temperature from 30 °C to 60 °C enhanced TRS yield 5.4-fold using SSF. Saccharification using fungal mash outperformed commercial enzyme cocktails, producing 1.2-fold higher TRS, demonstrating a low-cost alternative. Additionally, sorghum bran, a by-product constituting approximately 25% of the seed, exhibited substantial protease production (847.09 U/g, dry basis) by A. oryzae using bran particle sizes <0.6-0.3 mm, representing an 8.6-fold increase compared to A. awamori under solid-state fermentation (SSF). These findings demonstrate the transformative potential of fungal biotechnology in valorizing lignocellulosic biomass, fostering circular bioeconomy strategies, and renewable energy solutions. The proposed framework provides a scalable, green bioprocess for future industrial applications, contributing to sustainable agriculture and global energy security.