Mixed-microbe solid-state fermentation modulates the physicochemical and aroma profiles of Eucommia ulmoides leaf

Eucommia ulmoides leaf (EL) is rich in diverse bioactive constituents.

This study employed solid-state fermentation with Lactiplantibacillus plantarum and Bacillus subtilis to improve its quality and flavor. Changes in functional components, metabolites and flavor profiles were analyzed pre-and post-fermentation. Untargeted metabolomics based on UHPLC-MS and HS-SPME-GC-MS revealed 1,698 non-volatile and 827 volatile metabolites in EL and fermented EL.

Analysis of differential metabolites indicated that solid-state fermentation significantly modulated key metabolic pathways, including phenylpropanoid biosynthesis, carbohydrate metabolism, and amino acid metabolism. This metabolic reprogramming enriched the profile of pharmacologically active metabolites such as amino acids, peptides, flavonoids, and alkaloids, and altered the content of specific bioactive compounds: geniposidic acid and chlorogenic acid increased, whereas total flavonoids, polyphenols, and polysaccharides decreased. Flavor analysis revealed that 2-methylisoborneol, the key substance of earthy and musty flavor, was significantly reduced after fermentation, while the contribution of 2-sec-butyl-3-methoxypyrazine and damascenone, the characteristic aroma components of green leaf and fruit flavor, was increased.

These shifts collectively resulted in an improved overall flavor profile. This study establishes a theoretical foundation and technical framework for quality and flavor modulation of EL through solid-state fermentation with Lactiplantibacillus plantarum and Bacillus subtilis, supporting the development of functional EL products.