Reduction of Escherichia coli O157:H7 and naturally present microbes on fresh-cut lettuce using lactic acid and aqueous ozone

Abstract

Lactic acid plus aqueous ozone is an effective hurdle technology for fresh produce disinfection.

Disinfection of Ready-to-Eat Lettuce Using Polyhexamethylene Guanidine Hydrochloride

“…Pathogen inoculation was performed as described in our previous reports [19,20]. Briefly, nontoxic E. coli O157:H7 (NCTC12900) and L. monocytogenes (ATCC19115) were stored in glycerol solution at a ratio of 1:1.…”

“…The extent of damage to the lettuce after disinfection was evaluated by measuring electrolyte leakage as described by Wang et al [20], with minor modifications. Five grams of the sample was immersed in 250 mL distilled water for 20 s to remove the sanitizer residue, which can interfere with conductivity measurements.…”

“…The antibacterial mode of action of PHMG was discussed above. The antibacterial effects of organic acids are attributed to the high intracellular pH, which promotes the dissociation of acidic molecules after cell penetration, resulting in anion accumulation in the cell and toxic effects on the cell membrane, acid-sensitive proteins, DNA and RNA [18,20]. Chlorine primarily damages the cell membrane and leads to leakage of cellular macromolecules [26].…”

“…The use of different sanitizers (with different antibacterial mechanisms of action) is reported to result in additional microbial reductions compared to those obtained using a single type of sanitizer. For example, Wang et al [20] found that sequential washing of lettuce using lactic acid and aqueous ozone (AO) shortened the processing time by 30 s compared to lactic acid treatment alone, with further reductions of E. coli O157:H7 and naturally present microbial taxa. Combined use of CA and AO reduces E. coli and L. monocytogenes counts on lettuce and mushrooms to a greater extent than either agent alone [27,28].…”

Combination of polyhexamethylene guanidine hydrochloride and potassium peroxymonosulfate to disinfect ready-to-eat lettuce

“…Electrolyte leakage was analyzed according to the method of Wang et al 18 Lettuce samples (5 g) were immersed in 250 mL distilled water for 20 s to remove the sanitizer residue and then placed in 150 mL of distilled water. Aer standing for 30 min, the conductivity was measured and then the samples were placed at À20 C for 12 h. The samples were taken out to naturally thaw at room temperature, and the conductivity was measured again.…”