Water kefir fermentation of mixed plant-based extracts: effects on antioxidant activity and volatile composition.

Water kefir fermentation was applied to a mixture of hydrosoluble plant-based extracts from cashew nut, coconut, and quinoa to investigate fermentation performance and associated chemical transformations. A mixture experimental design evaluated the effects of substrate composition on microbial growth, physicochemical properties, antioxidant capacity, volatile profile, gastrointestinal stability, and sensory response. Fermentation significantly modulated kefir grain growth, organic acid production, ethanol formation, and carbon dioxide release, with quinoa exerting the strongest effect on fermentation dynamics. The selected centroid formulation exhibited balanced fermentation behavior, stable physicochemical characteristics, and relevant protein, lipid, mineral, and antioxidant contents. SPME-GC-MS analysis revealed pronounced changes in the volatile profile, including increased alcohol and ethyl ester formation and reduced aldehyde levels. In vitro digestion revealed differential microbial survival after the intestinal phase, with yeasts showing greater persistence than bacterial groups. Despite increased chemical complexity, the fermented beverage showed lower sensory acceptance, highlighting the need for process optimization.