Substrate-structure-oriented product prediction framework unlocking short-chain fatty acids profiles during anaerobic...

Anaerobic fermentation experiments using 16 pure substrates, integrated with metagenomic analyses, were conducted to investigate the association between substrate molecular structure and short-chain fatty acids (SCFAs) production profile. Substrate chemical properties were found to govern microbial community selection, metabolic pathway activation, and SCFAs profile, thereby enabling the development of a substrate-structure-oriented product prediction framework (SSOPPF). The six-carbon backbone and abundant hydroxyl groups of monosaccharides favored near-equal acetate and butyrate production. The three-carbon skeleton of glycerinum specifically drove propionate synthesis (49%). The carbon skeletons of amino acids determined product specificity; for example, branched-chain isoleucine yielded 83 % isovalerate, whereas aspartate, characterized by a succinate-like backbone, produced 69 % propionate. Amino acids simultaneously acted as acid precursors and endogenous pH buffers. This study advances beyond coarse predictions based on broad substrate classifications by preliminarily establishing a causal link from molecular structural features to product spectra, pending validation in complex fermentation systems.