Abstract:
Abstract: Slightly acidic electrolyzed water (SAEW) with pH 5.0-6.5 is produced by electrolysis of dilute hydrochloric acid or salt solution in a chamber without a membrane. SAEW can effectively kill various pathogenic bacteria as one of the most potential green disinfectants. However, SAEW is susceptible to being exposed to time, air, and illumination etc. The influence of SAEW for inactivation of Escherichia coli on white shrimp (Litopenaeus vannamei) under different washing conditions was investigated. At room temperature, the effectiveness of SAEW (with available chlorine concentration (ACC) of 20 mg/L, pH value of 6.1 and ORP of 812 mV) to inactivate Escherichia coli with different dipping times (2, 5 and 10 min), weight ratio of shrimp to SAEW (1:4, 1:10 and 1:20) was evaluated, and changes of ACC were also measured. For inoculation, each shrimp was determined to be intact, and then exposed to a 90°C water bath boiling for 20 min. to inactivate bacteria on the surface of shrimps. Each sample was inoculated with E. coli by spreading 0.5 mL onto each surface respectively and then placed in a clean bench for 20 min. to allow for the attached E. coli. The level of E. coli on the shrimp surface was ensured to be of approximately 6.0-7.0 lgCFU/mL, and bacterial cells on surfaces of shrimp or in residual solution after treatment were counted using a dilution plate count at 37°C for 24h onto nutrient agar, and shrimp that were not washed were used as a control. Moreover, the decay kinetics models of ACC in SAEW during disinfection were established. The effect of SAEW on meat quality was also evaluated, respectively from color, pH value, hardness, and the moisture distribution. The results showed that SAEW has a strong bactericidal activity against E coli. on white shrimp, while distilled water has a relative weaker role. As the action time prolonged, and the amount of SAEW increased, the bactericidal effect of SAEW was intensified. Meanwhile, the residue bacteria colony in SAEW was also reduced and expenses of active chlorine was increased as the action time was prolonged, and the amount of SAEW increased during the disinfection process. The effective order of time on the bactericidal activity of SAEW was 10 min > 5 min > 2 min under the same ratio of shrimp to SAEW, dipping in SAEW (weight ratio of shrimp to SAEW was 1:4) for 10 min reduced E. coli population from 6.6 to 3.9 lgCFU/mL, which better than the control treatment. E. coli counts in a residual solution can reduce by 1-2 lgCFU/mL. Increasing the amount of SAEW enhanced the bactericidal effect obviously. The decay of ACC and bactericidal kinetic followed first-order kinetics during the disinfection process, and the model had good predicted results. In addition, there was no significant differences between the treated meat quality by SAEW and the controls, respectively from color, pH, hardness, and the moisture distribution of white shrimp meat. Therefore, SAEW has a strong bactericidal activity, and does not affect the meat quality of white shrimp, and has a great potential for application compared with the traditional thermal treatment.