Purpose: The aim of this study was to investigate the effect of CAP on Escherichia coli and Salmonella spot inoculated on the surface of golden delicious apples.
Methods: Filtered air at a pressure of four bars and at a flow-rate of 17 liters/min were used for the plasma generation. The process parameters considered were plasma exposure time for 0.5, 1, 2, 3, and 4 minutes at a fixed distance of 35 mm and fixed input power of 200 Watts. Each treated spot inoculation was swabbed with wet sterile cotton swabs and a series of dilutions were performed. Each dilute (0.1 ml) was spread in duplicates on TSA plates and incubated at 37°C for 24 hours. All plate count data was converted to log CFU/ml.
Results: All treatments resulted in significant (P<0.05) time-dependent reduction compared to untreated control. The reductions ranged from 1.4 to 5.3 log CFU/ml and 0.6 to 5.5 log CFU/ml for E. coli (ATCC 25922) and E. coli (ATCC 11775), respectively. The reduction of Salmonella Typhimurium (ATCC 13311) and Salmonella Choleraesuis (ATCC 10708) ranged from 2.8 to 4.8 and 1.3 to 5.3 log CFU/ml, respectively. Escherichia coli and Salmonella were inactivated by approximately 5.5 log CFU/ml at four minutes at a distance of 35 mm. The microbial inactivation effect of cold plasma treatment can be attributed to several synergistic mechanisms, including the generation of ultraviolet irradiation, ozone, charged particles, and oxygen radicals, in addition to other reactive species.
Significance: According to our results, CAP treatment was effective in the inactivation of E. coli and Salmonella on apples. However, further investigation is needed for elucidating the organoleptic and nutritional quality changes of fresh produce after plasma treatment.