Characterization of slightly acidic electrolyzed water (SAEW) on effective disinfection against microbial safety and retention of phenolic compound in SAEW treated fresh romaine lettuce

Objectives: This study investigated the effects of processing parameters, specifically the flow rate and the combination of diluted HCl and salt (NaCl) at different concentrations, on the properties of slightly acidic electrolyzed water (SAEW) that was produced. Materials and Methods: The properties of the SAEW that were analyzed included pH, oxidation-reduction potential (ORP), available chlorine concentration (ACC), and generated hypochlorous acid (HClO) concentration. Meanwhile, the total aerobic bacteria and total phenolic content retention were determined. Results: NaCl alone resulted in the lowest pH (<4) and the highest ORP values (>1000 mV). Increasing the HCl concentration significantly raised the pH to greater than 5 and lowered the ORP values of SAEW, with the highest pH (5.7) observed with 1.5% HCl and 5% NaCl. The highest HClO concentration of 19.65±1.03 mg/L was obtained with 1.5% HCl:5% NaCl. Interestingly, the concentration of NaCl had no significant effect on the production of HClO. Furthermore, different concentrations of combined NaCl and HCl significantly influenced the inactivation efficiency on total aerobic bacteria count and changes in phenolic compound content. Increasing HCl concentrations from 0.5% to 2.0% led to an increase in the reduction of aerobic bacteria counts from 2.51 to 4.22 log colony-forming units (CFU)/g with 5% NaCl and from 2.49 to 3.52 log CFU/g with 10% NaCl. Flow rates significantly contributed to the change in HClO formation and altered the properties of the produced SAEW. The results indicated that SAEW treatment significantly reduced total aerobic bacteria counts. A lower flow rate (0.3 L/min) produced the highest log reduction. Additionally, SAEW treatment led to a reduction in phenolic content, even though a considerable amount was retained at lower HClO concentrations. Conclusions: These findings offer valuable information on optimizing SAEW treatment protocols for enhancing microbial safety and extending the shelf life of fresh produce, while considering the impact on the content of phenolic compounds.