Coffea arabica Infusion as a Potential Substrate for Kombucha Fermentation Modulates Microbial Populations, Symbiotic Culture of Bacteria and Yeast Ultrastructure, and Functional Attributes: Insights From Machine Learning.

Kombucha is traditionally produced from sweetened Camellia sinensis tea fermented by a symbiotic culture of bacteria and yeasts (SCOBY). However, limited information is available on the effects of replacing tea with Coffea arabica infusion on fermentation parameters, microbial ecology, and overall quality of the beverage. This study evaluated the effects of substituting green tea with C. arabica infusion (25%-100%, v/v) during kombucha fermentation on fermentation kinetics, microbial populations, SCOBY structure, and physicochemical, functional, and sensory attributes. Coffee substitution reduced sugar consumption rates without significantly affecting final pH (2.8-3.2) or titratable acidity (∼0.4). Increasing coffee proportions markedly reshaped microbial populations, reducing acetic acid bacteria and increasing lactic acid bacteria, thereby shifting metabolism toward lactic acid production. Structural analyses revealed preserved SCOBY integrity, with a more porous cellulose network in coffee-based formulations. Total phenolic content decreased after fermentation in most treatments, whereas the 100% coffee kombucha remained stable and maintained antioxidant capacity. GC-MS analysis identified 111 volatile compounds, and multivariate and machine learning approaches revealed coffee-associated biomarkers associated with lactic acid and aroma-active compounds. Overall, C. arabica infusion proved to be a suitable alternative substrate for kombucha fermentation, enabling substrate-driven modulation of microbial dynamics and metabolic profiles while maintaining product safety and functional potential. PRACTICAL APPLICATIONS: Replacing green tea with C. arabica infusion in kombucha production enables the development of beverages with differentiated microbial, chemical, and sensory profiles while maintaining fermentation performance and safety. Coffee-based kombucha promotes a shift toward lactic acid-oriented fermentation, distinct aroma signatures, and functionality without requiring significant changes to conventional SCOBY-based processes. From a practical perspective, coffee infusion is a feasible strategy for product diversification, allowing manufacturers to modulate fermentation outcomes through raw material selection and to support the development of innovative, scalable, and consumer-oriented kombucha beverages.