Emmanouil Tsavdaridis

Efficient use of agro-industrial residues is central to developing a circular bioeconomy. In this study, apple pomace was used as a feedstock for fermentation with water kefir cultures to investigate the formation of bioactive compounds and evaluate their functional biological effects. The effects of fermentation in a cement tank were compared to a reference fermentation system using a conventional glass vessel, focusing on physicochemical parameters and biological activity. Despite differences in pH evolution, no significant differences between the two fermentation systems were found in antioxidant capacity, total phenolic and carotenoid content, or inhibitory activity against platelet aggregation. Lipid extracts from both systems showed strong antioxidant properties and pronounced inhibitory activity against platelet-activating factor (PAF)- and ADP-induced aggregation, with significantly lower IC₅₀ values for PAF (p < 0.05), indicating enhanced anti-inflammatory specificity. These effects may be attributed to the synergistic interaction of fermentation-derived bioactives, including polar lipids, aglycone flavonoids, and carotenoids. Importantly, fermentation in a cement tank did not compromise biofunctional performance, highlighting its potential as a low-cost and scalable alternative for bioprocessing. Overall, these findings demonstrate that water kefir fermentation can efficiently convert low-value fruit residues into bioactive-rich matrices, providing a sustainable and environmentally friendly approach aligned with EU and UN circular economy frameworks for waste reduction and resource valorization.