Enhancing Glucuronic Acid and Bacterial Cellulose Yield in Kombucha via Valorization of Male Jelly Fig (Ficus pumila L. var. awkeotsang)

Abstract

Male jelly fig (Ficus pumila L. var. awkeotsang) syconia are an underutilized by-product in Taiwan. This study evaluated male fig powder (0-2%, w/v) as a substrate for producing male fig-altered kombucha (FK) using a defined co-culture of Komagataeibacter xylinus and Saccharomyces cerevisiae. Fermentation markedly reshaped FK metabolites. Glucuronic acid increased in a dose-associated manner, reaching 6.63 g/L in 2% FK, whereas vitamin C declined during fermentation but remained highest in 2% FK. Gallic acid increased and peaked at 0.5% FK (320.75 mg/L), while acetic and succinic acids showed formulation-dependent patterns; conversely, caffeine decreased in all male fig-containing groups. FK also exhibited concentration-dependent color divergence from the control at day 9 (Delta E* up to 17.81 at 2% FK). Numerical increases in DPPH and TPC were observed; however, no significant differences were detected among the treatments. Importantly, male fig supplementation substantially enhanced kombucha bacterial cellulose (KBC) yield (0.56 to 7.28 g/L from 0 to 2% FK) without compromising high water content (similar to 96-99%) or swelling (similar to 90-94%). FTIR confirmed retention of the cellulose backbone, SEM showed formulation-dependent fibril diameters, and TGA indicated higher early-stage thermal stability with dose-dependent shifts in main degradation behavior. Collectively, male figs can be valorized to produce FK with altered metabolite profiles and improved KBC productivity.