Unlocking Product Spectrum in Anaerobic Fermentation: A Substrate Structure-Oriented Predictive Framework for Short-Chain Fatty Acid Production

The unpredictable product spectrum in anaerobic fermentation of organic solid waste has long hindered its industrial application, with traditional substrate categorization offering limited predictive power. This study introduces a groundbreaking Substrate Structure-Oriented Product Predictive Framework (SSOPPF) that directly correlates molecular structural features-such as functional groups, carbon chain length, branching, and ring conformation-with SCFAs production profiles. Through systematic experimentation with 16 pure substrates under controlled batch fermentation and integrated metagenomic analysis, we demonstrate that substrate chemistry acts as the primary selector of microbial community structure, metabolic pathway activation, and ultimate product distribution. Key innovations include the discovery that glycerinums three-carbon backbone specifically drives propionate synthesis; amino acid side-chain properties precisely determine product specificity (e.g., isoleucine to isovalerate, aspartate to propionate); and amino acids serve dual roles as both acid precursors and intrinsic pH buffers, enabling stable high-rate acidogenesis without chemical additives. By transcending empirical approaches and establishing a causality chain from molecular structure to product spectrum, this work provides a powerful theoretical and practical foundation for the predictive design of anaerobic fermentation processes, opening new avenues for precision waste valorization and carbon-efficient biorefining.