A research has found that if kimchi that has been purchased or made at home is left at room temperature for about a day and refrigerated starting the day after, the fermented kimchi can be consumed safely and deliciously.
This finding was contained in the results of a research project conducted by the Gyeonggi-do Institute of Health and Environment of Gyeonggi province, South Korea, which examined the interrelation between the fermentation period of kimchi sold in retail and pathogenic germs as well as lactic acid bacteria. The institute announced the results of the project on Apr. 13.
From June to November last year, the provincial institute tested two types of South Korean kimchi that are sold at large discount stores and online.
Kimchi samples used for testing were artificially inoculated with highly dangerous food poisoning bacteria such as Salmonella, Shigella, Listeria monocytogenes, and E. coli. For the next 30 days, any changes in the viable cell count of food poisoning bacteria and lactic acid bacteria were kept track of.
The result of the experiment showed that the higher the fermentation temperature and the longer the fermentation period of kimchi, the proliferation of pathogenic bacteria that cause food poisoning was more inhibited and the chances of them dying increased.
In the case of kimchi stored at room temperature of 25 degrees Celsius, Salmonella got wiped out as quickly as within a day or two. The viable cell counts of E. coli, Shigella, and Listeria monocytogenes also rapidly decreased and they died out within about 3 to 6 days.
During this time, the highest viable cell count of lactic acid bacteria was reached in a day, and the hydrogen ion concentration, or pH, stayed at between 3.93 and 4.33. The experiment confirmed that if kimchi is fermented for a short period at room temperature, rapid reduction of pH level resulting from the generation of lactic acid and accumulation of other organic acids can lead to the death of pathogenic bacteria.
On the other hand, at 4 degrees Celsius, which is the refrigeration temperature that kimchi is stored at in homes, Salmonella died out in 10 to 16 days, Shigella in 23 days, and E. coli in 27 days (there were even cases where bacteria survived depending on the kimchi tested). Listeria monocytogenes were even found to maintain their viable cell count for 30 days.
Fermentation of lactic acid bacteria progressed gradually at low temperatures, and it took 6 to 13 days, with the exception of Salmonella, to reach the maximum count. Furthermore, the lactic acid generated by fermented lactic acid bacteria was not able to effectively contain food poisoning bacteria.