Partial NaCl replacement with KCl enhances microbial dynamics and antioxidant potential in fermented Nabali Baladi olives

• Yeast was the predominant microorganism in Nabali Baladi olive fermentation. • Replacing NaCl with KCl enhances the diversity of yeast species in fermentation. • Equal amounts of NaCl and KCl promote highest level of phytochemicals in olives. • Newly identified Candida species were involved in the fermentation process The aim of this study was to evaluate the effect of the partial replacement of sodium chloride (NaCl) with potassium chloride (KCl) on the microbial communities, total phenolic (TPC) and flavonoid (TFC) contents, as well as the antioxidant activities of traditionally fermented green Nabali Baladi olives grown in Jordan. Five brine solutions containing different concentrations of NaCl and KCl were used to ferment green Nabali Baladi olives, using the traditional Jordanian fermentation method. Samples were analyzed for yeast, lactic acid bacteria (LAB), and total bacterial count via the viable count method. Purified yeast isolates were identified by sequencing the 26S rDNA region. TPC and TFC and antioxidant activity (DPPH and ABTS + free radical scavenging assays) were determined using spectrophotometry assays. Results showed that yeast was the predominant microorganism found in fermented olives, with a complete absence of LAB. Members of the genus Candida was predominant in 10% NaCl brine, whereas members of the genus Saccharomyces were found to the most prevalent microorganism in mixed or KCl-rich brines. A significant increase in TPC, TFC, and antioxidant activities were also detected by day 90 of fermentation, especially in brine with equal amounts of NaCl and KCl (5%: 5%). This study highlights the potential replacement of NaCl with KCl in the fermentation process of olives, which enhanced the functional properties of fermented olives as well as reducing their sodium content, with the 5% NaCl + 5% KCl brine for 90 days of fermentation, yielding the most favorable results for the microbial activities, TPC and TFC, and antioxidant activities .