عنوان مقاله [English]
Background and objectives: Spices and medicinal plants, like other agricultural products, have been contaminated with bacteria, soil, and insects during the process of planting, harvesting, transporting, and processing. One way to remove contamination is to use gamma radiation. Therefore, the aims of the present study were to evaluate the effect of gamma irradiation (0, 5, 10, and 15 kGy) on color parameters and microbial population of Mentha longifolia L. plant packaged under modified atmosphere (MAP), vacuum, and aerobic conditions, and also its effect on chemical composition and antioxidant and antimicrobial properties of M. longifolia essential oil.
Materials and methods: M. longifolia L. plant was collected in spring (April-May) 2020 from Gilanegharb, located in Kermanshah, Iran. Irradiation of the packaged M. longifolia plant samples was performed under MAP (N2 = 100%), vacuum and aerobic conditions using doses of 5, 10, and 15 kGy (radiation source = 60 cobalt and dose rate = 4.18 kGy h-1) in the Atomic Energy Organization of Iran. After irradiation, the color parameters and microbial population of the packaged samples were evaluated. Moreover, the chemical composition of M. longifolia essential oil using gas chromatography–mass spectrometry and antioxidant property via 2, 2-diphenyl-1-picrylhydrazyl radical scavenging and Beta-carotene bleaching inhibition were evaluated. Study on the antimicrobial activity of M. longifolia essential oil against Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, and Bacillus subtilis using disk diffusion method was performed.
Results: Results of this study indicated that gamma irradiation under 5 and 10 kGy (aerobic condition) and 15 kGy (aerobic, vacuum, and modified atmosphere conditions) resulted in significant reducing a and b parameters and increasing L parameter in comparison with control group (P < 0.05). The gamma irradiation under 10 and 15 kGy inhibited the growth of total viable bacteria, coliforms as well as yeast and mold in packaged samples into lower than the count limit of 1 log CFU g-1. Based on our findings, nineteen chemical compounds were identified in Mentha longifolia essential oil. Eucalyptol (18.23%-19.55%), menthone (12.36%-13.55%), and pulegone (47.69%-49.55%) were the main identified chemical constituents in Mentha longifolia essential oil. Moreover, gamma irradiation (0, 5, 10, and 15 kGy) and types of packaging (aerobic, vacuum, and modified atmosphere conditions) hadn’t effects on the change of chemical compounds, as well as antimicrobial and antioxidant properties of Mentha longifolia essential oil (P > 0.05).
Conclusion: The results of this study showed that the use of gamma radiation at doses of 10 and 15 kGy is a suitable method for disinfection of packaged M. longifolia under aerobic, vacuum and MAP conditions, without affecting their chemical composition and antimicrobial and antioxidant properties.