The effect of some alternative decontamination methods on the microbiological and chemical quality of oregano

In this study, the effects of thermal (steam sterilization) and non-thermal (gamma irradiation, UV irradiation and ozonation) decontamination methods on microorganisms (total aerobic mesophilic bacteria, yeast mold and Enterobacteriaceae), pyrrolizidine alkaloids, volatile compounds and color values in oregano were investigated. It was determined that the most effective methods in inactivating microorganisms were steam sterilization and gamma irradiation. These treatments resulted in reductions of 0.87-2.15 log cfu/g in the total number of aerobic mesophilic bacteria and reduced the numbers of yeast, mold and Enterobacteriaceae to below detectable levels. Steam sterilization treatment resulted in increases in the levels of pyrrolizidine alkaloids (PAs) and decreases in the levels of their N-oxide forms (PANOs). It reveals that the heat treatment transforms PANOs into corresponding PAs. UV irradiation and ozonation treatments were applied for 1, 2, 4 and 8 h, and short-term treatments (1 and 2 h) were not effective in microbial inactivation. However, longer treatments (4 and 8 h) resulted in a certain degree of microbial inactivation. Gamma and UV irradiation could not cause any decrease in the PA/PANO levels of the oregano. On the other hand, ozonation treatment caused significant decreases in the levels of PAs/PANOs. After this treatment, decreases of 54.4%, 53.9%, 61.6% and 61.4% were observed in europine-N-oxide, europine, lasiocarpine-N-oxide and lasiocarpine levels, respectively. Steam sterilization, UV irradiation and ozonation significantly changed the composition of volatile compounds in the oregano and caused formation of some new compounds. However, it was determined that gamma irradiation treatment did not have any significant effect on the volatile compounds of the oregano. Steam sterilization, gamma irradiation and UV irradiation changed the color values of the oregano to a certain extent, but the most noticeable color differences were determined after the ozone treatments.