Enhancing the biochemical and functional properties of water kefir: Comparative effects of different water sources with emphasis on deep ocean water

Water kefir has gained popularity as a traditional fermented beverage associated with various health benefits. In this study, water kefir was fermented with deionized water (DW), deep-ocean water (DOW) and natural mineral water (NMW) to compare physicochemical and health-promoting traits. DOW kefir (DOWK) reached pH 3.03 and titratable acidity 9.54 g/L, versus 3.37/1.52 g/L (DWK) and 3.69/4.46 g/L (NMWK). HPLC showed DWK contained only acetic acid (0.10 g/L), while DOWK and NMWK accumulated gluconic acid (0.26–0.31 g/L), lactic acid (0.13–0.19 g/L), and higher acetic acid (1.60–4.24 g/L). All grains bore α-1,6 glucosyl linkages. DOWK displayed the greatest antioxidant capacity and α-glucosidase inhibition, 1.13–3.51-fold above DWK/NMWK, and the strongest antibacterial action against Salmonella , E. coli and S. aureus (MIC 25–50 % v /v). DWK showed minimal inhibition. The mineral profile of DOW thus stimulates microbial metabolism and yields water kefir with superior health-related properties, supporting its use in value-added functional beverages. • Water kefir was fermented using deionized water (DW), deep ocean water (DOW), and natural mineral water (NMW). • DOW and NMW kefir contained gluconic and lactic acids, while all samples contained acetic acid. • DOW significantly enhanced antioxidant activities (FRAP, ABTS, ORAC) and α-glucosidase inhibition by up to 3.5-fold. • DOW-derived kefir exhibited superior antimicrobial effects against S. typhimurium , S. enterica , E. coli , and S. aureus . • Sensory characteristics of water kefir were differentiated using an electronic tongue system.