Synergistic yeast co-culture and pretreatment optimization for enhanced single cell protein production from agro-waste

The escalating global demand for sustainable protein sources, alongside the imperative to manage agro-waste, has intensified research into innovative bioconversion technologies. Single cell protein (SCP) production through liquid-state fermentation (LSF) offers a promising approach by transforming agro-waste residues into high-value microbial biomass. This study investigates the optimization of acid pretreatment and yeast strains to maximize SCP yield, contributing to a circular bioeconomy. In the initial phase, single and co-culture yeast strains were evaluated for SCP production using YPD broth and agro-waste substrates. Over five days of fermentation, Saccharomyces cerevisiae yielded a maximum biomass of 1.8 g/L, while its co-culture with Candida krusei achieved 4.58 g/L, with protein contents of 45 % and 44.5 %, respectively. In the second phase, agro-waste pretreatments were optimized using Response Surface Methodology (RSM) with a three-level factorial model, where temperature, hydrochloric acid (HCl) concentration, and residence time served as independent variables. Optimal conditions (87.5 °C, 3 % HCl, 90 min) resulted in 4.6 g/L biomass, 2.67 g/L protein, 7.24 g/L nitrogen, and 0.72 g/L non-purgeable organic carbon. In the final phase, a 30-day continuous fermenter run under optimized conditions demonstrated scalability, achieving a peak biomass of 16.9 g/L and a microbial protein yield of 63.3 % on Day 7. These findings underscore the potential of strain-substrate synergies and optimized pretreatment for high-yield SCP production. By valorizing agro-waste, this approach offers a sustainable solution for protein production and waste management, advancing the transition toward a circular bioeconomy and addressing global challenges in food security and environmental sustainability.