Mechanism Of Electrolyzed Water On Inactivation Of Bacterial Vegetative Cells And Spores

The quality of brown rice and its nutrient and physiological components could be improved by germination. Germinated brown rice is becoming widely popular healthy food. Germinated brown rice is produced under the ceretain temperature and humidity, which is also appropriate for microorganism to grow and reproduce. It is critical to control the growth of microorganism to ensure germinated brown rice production and food safety. Electrolyzed oxidizing (EO) water has been broadly used in many fields including agricultural production and food processing. This study focused on the issue of microbial contamination during brown rice germination and used EO water at different conditions to inactivate bacterial vegetative cells and spores in pure culture and on brown rice. And then, the status of bacterial cells after EO water treatment was analysed by flow cytometry assay. The details of this study were shown as follows:(1) Inactivation of bacterial vegetative cells by EO water. Gram-negative, non-spore forming bacteria (Escherichia coli O157:H7) and Gram-positive, spore-forming bacteria(Bacillus subtilis) vegetative cells in pure culture were disinfected by EO water. The effects of different available chlorine concentrtions (ACC), different initial bacterial concentrations and centrifugations on bactericidal efficacy were determined. Moreover, DNA, protein and conductivity of bacterial cells after EO water treatment were also determined. The results showed that both acidic electrolyzed water (AEW) and slightly acidic electrolyzed water (SAEW) processed a high efficacy on bacteria inactivation, and the antimicrobial effect increased with increasing ACC, decreasing initial bacterial concentration and centrifugation times. The concentration of DNA, protein and conductivity was also augmented with elevated centrifugation times.(2) Spores inactivation by EO water. The effect of EO water with different ACC on inactivation of B. subtilis and B. cereus spores for different treatment time in suspension and on carriers was determined. The results indiacted that SAEW with ACC of 120 mg/L treated B. subtilis and B. cqreus spores for 2 min in suspension achieved the spore population at non-detectable level and AEW and SAEW with 60 mg/L ACC treated B. subtilis and B. cereus spores for 6 min obtained the same result as well. The sporicidal efficacy of EO water in suspension was higher than on carriers, and organics significantly reduced its sporicidal efficacy (p<0.05).(3) Detection of bacterial status after EO water treatment. E. coli O157:H7 was treated with EO water at different ACC for 30 s, and then the methods of flow sytometry assay as well as plate count, enrichment, resuscitation were used to detect and analyse the status of treated bacterial cells-viable, viable but non-culturable (VBNC) and dead. The results showed that EO water treated cells could enter VBNC. The number of VBNC cells firstly decreased with increasing ACC and then decreased, and finally VBNC cells become dead cells.(4) Brown rice was used as a case in this study. The effect of EO water with different ACC for shortly treated on decontamination of natural microbiota on the surface of brown rice was determined. On the other hand, sporicidal efficacy of EO water was also taken into consideration to control the population of B. cereus spores on brown rice. Water absorption rate, germination potential, germination percentage and sprout length were detected to evaluate the effect of EO water on the properties of germinated brown rice. The results showed that AEW with ACC of 150 mg/L for 30 min treatment could completely remove the natural microbiota on brown rice and has no negative effect on the properties of brown rice germination, while long time (24 h) treatment by AEW could slightly inhibit the germination of brown rice. Application of SAEW in brown rice soaking could enhance the properties of brown rice germination. The efficacy of EO water on inactivation and control the population of B.cereus spores inoculated on brown rice was improved by EO water changed for 5 times during brown rice soaking.