Enumeration of Chlorine-injured Coliform Bacteria of Shredded Cabbage Stored in MAP

Chlorine-based sanitizer can induce coliform bacteria to be in a nonlethal, injured state. The degree that coliforms were injured sublethally by using electrolyzed water containing chlorine on shredded cabbage was evaluated during storage in a modified atmosphere packaging (MAP) at 5 and 10°C. The thin agar layer (TAL) method was used to recover and enumerate injured bacteria. Treatment with electrolyzed water containing 20 ppm available chlorine for shredded cabbage reduced the counts of coliforms by 0.5 to 1.1 logs and caused sublethal injury from 42 to 77%. When shredded cabbage with or without electrolyzed water treatment was stored in 3 types of package films with an oxygen transmission rate (OTR) of 500, 3000, and 10000 ml·m^-2·day^-1·atm^-1 for 5 days at 10°C and 7 days at 5°C, the CO₂ accumulated to 15, 10, and 5%, respectively, and O₂ was depleted to 5, 10, and 15%, respectively, regardless of the treatment and storage temperature. Coliform counts on TAL plates increased from 4.5 to 8.5 log CFU·g^-1 during 5 days of storage at 10°C and increased from 4.5 to 6.5 log CFU·g^-1 during 7 days of storage at 5°C. Chlorine-injured coliforms were not seen on shredded cabbage throughout the storage period at both temperatures, except for the samples on the initial day that had injury ranging from 46 to 83%. Since a preliminary study showed that the chlorine level of 1 to 2 ppm could be effective in sublethally injuring Escherichia coli O157:H7, shredded cabbage was inoculated with chlorine-injured E. coli O157:H7 (percent injury: 45%) by mixture with electrolyzed water containing 1 ppm available chlorine, and then stored in a MAP using 2 types of package films with either an OTR of 500 or 10000 ml·m^-2·day^-1·atm^-1. While the packages approached an equilibrium of 5% CO₂ and 15% O₂ in a high OTR film and 15% CO₂ and 5% O₂ in a low OTR film at 5 and 10°C, injured E. coli O157:H7 on shredded cabbage was detected. Injury was 55% in a low OTR film for 5 days at 10°C and 73% in a high OTR film for 7 days at 5°C. These results indicated that chlorine-injured E. coli O157:H7 on fresh-cut cabbage were capable of exhibiting different degrees of injury during storage in a MAP regardless of the storage atmosphere and temperature.