2019 ASHS Annual Conference

Chemical disinfectants can induce bacteria to be in a sublethally injured state. We initially determined the effects of individual disinfectant treatments that included electrolyzed water (50 ppm available chlorine), alcohol agent (5% ethanol), calcined calcium agent (91% calcium oxide), and fumaric acid agent (20% fumaric acid), followed by sequential treatments with these disinfectants on the induction of sublethally injured coliform bacteria present on shredded cabbage. Subsequently, we evaluated the viability of injured coliforms on shredded cabbage treated with the combination of two disinfectants and then stored in a modified atmosphere packaging (MAP) at 5ºC for 5 days. The thin agar layer (TAL) method was used to recover and enumerate injured bacteria. In an in vitro study using a pure culture of Escherichia coli, it was found that injury of E. coli ranged from 66 to 100% in either electrolyzed water containing 1-2 ppm available chlorine, 3-9% alcohol agent, 0.03-0.1% calcined calcium agent, or 0.02% fumaric acid agent. In an in vivo study using shredded cabbage, coliform counts were reduced as the concentration of each disinfectant increased, and only the treatments with electrolyzed water containing 25-35 ppm available chlorine or 0.1% fumaric acid agent caused sublethal injury at a 51-58% level. When electrolyzed water containing 25 ppm available chlorine was combined with either 2% alcohol agent, 0.05% calcined calcium agent, or 0.1% fumaric acid agent, these combinations of the disinfectants reduced the coliform counts markedly and did not induce sublethal injury to coliforms on shredded cabbage. Shredded cabbage, nontreated or treated with electrolyzed water followed by either alcohol agent, calcined calcium agent, or fumaric acid agent, was stored in a MAP (an equilibrium of 8% CO₂/10% O₂ for nontreated samples and 4% CO₂/15% O₂ for treated samples). Coliforms injured at a 55-78% range were detected on samples nontreated and treated with electrolyzed water followed by fumaric acid, and coliform counts increased more than 1 log from the initial counts after 5 days of storage. In comparison, the treatment with electrolyzed water followed by either the alcohol agent or calcined calcium agent prevented bacterial proliferation and occurrence of sublethal injury throughout the storage period. These results indicated that the combination of two disinfectants would be helpful in reducing bacterial counts and suppressing the degree of sublethal injury on fresh-cut cabbage after treatment and during subsequent MAP storage.