Sodium percarbonate (SP) is a relatively low-cost and stable solid oxidizer with a small environmental burden. It is often included in cleansers for sanitizing circulating water pipes and as bleaching reagents in laundry, although the bactericidal effect of SP is lower than that of chlorine-based agents. 2-[Bis (carboxymethyl) amino] propanoic acid-chelated copper (MGDA-Cu) was added to increase the effect of SP. The addition of 12 µM MGDA-Cu increased the bactericidal effect of 0.5 wt% SP against Staphylococcus aureus even in the presence of 0.3 wt% BSA, which is an experimental model of organic stain to protect bacteria from SP. MGDA-Cu was effective against Escherichia coli only in the absence of BSA and showed little effect against Bacillus subtilis. It enhanced the effect of SP to decrease the viscosity of sodium alginate, which is one of the major components of biofilms. The effect of MGDA-Cu on sanitization was also evaluated by 16S rRNA amplicon sequencing of the bacterial flora of the biofilm on an experimental model of a circulating water pipe. The structure of the bacterial flora was more influenced by a cleanser containing both MGDA-Cu and SP than a cleanser with only SP, suggesting that MGDA-Cu increases the sanitization effect.

Dishwashers are one of the sources of bacterial contamination in dishes despite the fact that they comprise extreme environments due to the high temperature, high pH, and the presence of detergents during their operation. In this study, viable bacteria were isolated from 6 door-type and 8 conveyor-type dishwashers that were being used in food service facilities. Each door-and conveyortype dishwasher was divided into 6 and 9 sections respectively. Thermophilic bacteria, which grow at 60˚C, were obtained from 5 sections of door-type dishwashers, but obtained from one section of conveyor-type dishwashers tested. The 16S rRNA sequences of the cultured isolates revealed that fewer Gram-negative bacterial strains were found in door-type dishwashers than in conveyor-type dishwashers. The most frequently identified bacterial species in the samples tested were spore-forming bacteria, such as Bacillus and Anoxybacillus species. This study highlights the vulnerabilities presented by dishwashers used in food service facilities.