An Investigation into the Effect of Gamma Irradiation on Microbial Load of Medicinal Plant of Peppermint, Iranian Thyme, Summer Savory and Lemon Balm

Gamma irradiation can be used to increase post harvest quality of medicinal plants by decreasing microbial load and decontamination. Microbiological changes associated with food irradiation include the reduction or elimination of spoilage and pathogenic microorganisms, insect disinfestation and parasite disinfection. This factorial experiment was conducted on the basis of randomized complete block design with three replications. The effects of gamma irradiation on decreasing the microbial load of some medicinal plants including (Mentha piperita), lemon balm (Melissa officinalis), Summer savory (Satureja hortensis) and (Zataria multiflora) were investigated. Leaves of Lemon Balm, summer savory, pepper minit and thyme were irradiated at dosages of 3, 7, 10 and 15 KGy by a Co60 source, then total count, total Coliform and mold and yeast of the samples were studied. Gamma irradiation decreased microbial load of medicinal plant samples. The microbial load was detected in samples treated with 15 KGy radiation and control. Also, the result showed the highest and the lowest microbial load in peppermint and Iranian thyme, respectively. Results of this study show that gamma irradiation can be used as an important decontamination method to reduce the microbial load of medicinal plants.