Use of phytic acid and hyper-salting to eliminate Escherichia coli O157:H7 from napa cabbage for kimchi production in a commercial plant

The aim of this study was to develop a new salting method using natural phytic acid (PA) to ensure the microbiological safety and quality of salted napa cabbage used for kimchi production. The production of salted napa cabbage involves several stages: trimming, hyper-salting (20% NaCl) for up to 1h, salting (10% NaCl for 10–18h), three sequential washes in water (30s for each), and draining (2h). Two separate experiments were performed: one to determine the appropriate treatment conditions and a second to validate applicability under commercial conditions. In Experiment I, the effects of hyper-salting with PA on Escherichia coli O157:H7 numbers were tested in the laboratory. The following variables were monitored: 1) PA concentration (1, 2, 3%, w/w); 2) the ratio of the sample weight to the total volume of the solution (1:1.5, 1:3, or 1:6); 3) the hyper-salting time (30 or 60min); and 4) the salting time (2, 5, or 8h). A procedure that achieved a >5-log reduction in the E. coli O157:H7 population was then tested in an actual kimchi processing plant (Experiment II). The results from Experiment I showed that bactericidal efficacy increased as all the measured variables increased (p<0.05). Hyper-salting with 2% PA at a sample-to-water ratio (w/v) of 1:3 and 1:6 for 60min resulted in a >5-logCFU/g reduction in the E. coli O157:H7 population. Further salting for 5h completely eliminated (<1-logCFU/g) all bacteria. Thus, hyper-salting with PA 2% at a sample-to-water ratio of 1:3 for 60min, followed by salting for 5h, was tested under large-scale production conditions. The results revealed that the initial aerobic plate counts (APC), total coliform counts (TC), and fecal coliform counts (FC) were 6.6, 3.4, and 2.8-logCFU/g, respectively. The selected protocol reduced these values by 3.7-, >2.4-, and >1.8-logCFU/g, respectively. The 5h salting step maintained the TC and FC at <1-logCFU/g; however, the APC recovered somewhat. The pH and salinity of the treated salted napa cabbages were within the ranges required for kimchi production (pH5.1–5.3 and 1.5–2.0%, respectively). These results suggest that this novel method of salting food ensures microbiological safety and reduces the production time.