Sustainable co-fermentation of seagrape (Caulerpa lentillifera) and coffee cherry pulp: Enhancing bioactivity and stability for functional beverages

• Fermentation enhanced bioactive compounds in Caulerpa lentillifera and coffee cherry pulp. • Lactiplantibacillus plantarum TISTR 2070 improved antioxidant activity and LAB viability. • LC-QTOF-MS identified phenolic acids, peptides, and alkaloids linked to bioactivity. • PCA revealed strong correlations between antioxidant activity and sensory quality. • The process reduced cytotoxicity and promoted sustainable functional beverage development. Fermentation of seagrape seaweed ( Caulerpa lentillifera ) with Lactiplantibacillus plantarum and supplemented with coffee cherry pulp enhances microbial viability, bioactive compound content, and antioxidant activity while reducing cytotoxicity and improving sensory acceptance. The co-fermented formulation containing 50 g/L seagrape, 25 g/L coffee cherry pulp, L. plantarum TISTR 2070, and 30 g/L sucrose exhibited the highest total phenolic content and antioxidant capacity, with DPPH, FRAP, and ABTS values significantly exceeding those of the unfermented control ( p ≤ 0.05). Cold storage at 4°C demonstrated that the fermented beverage retained its antioxidant properties and maintained microbial viability with minor changes in sugar content and pH. Additionally, cytotoxicity testing on human colon cells demonstrated that fermentation markedly reduced cytotoxicity, with the CC 50 increasing from 16,020 ± 445.6 µg/mL (unfermented SG) to 25,860 ± 336.6 µg/mL in the co-fermented sample ( p ≤ 0.05), indicating improved safety for human consumption. Sensory evaluation confirmed that the fermented beverage was more accepted than the unfermented counterpart, with improvements in taste, mouthfeel, and overall preference. Multivariate analysis by PCA further revealed strong correlations between microbial activity, antioxidant capacity, and sensory attributes. LC-QTOF-MS analysis confirmed the release and biotransformation of diverse bioactive metabolites during fermentation, contributing to the enhanced functional properties of the final product. With its enhanced bioactivity, stability, reduced cytotoxicity, and superior sensory attributes, co-fermentation of seagrape and coffee cherry pulp presents a promising strategy for the development of health-promoting functional beverages.