How gamma radiation affects antimicrobial potential of medicinal plants: Mentha x piperita L. as a case study
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Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013), C2TN (UID/Multi/04349/2013), grant to A. Fernandes (SFRH/BPD/114753/2016) and L. Barros contract; European Structural and Investment Funds (ESIF) (Regional Operational Program Norte 2020, Project ValorNatural®); Rural Development Program (Project MicoCoating, PDR2020-101-031472); International
Atomic Energy Agency (IAEA) Coordinated Research Project D61024 DEXAFI.
Medicinal plants are being used by the food and pharmaceutic industries to extract relevant compounds. To be used in these industries as raw materials, it is required the non-presence of microorganisms. Therefore, it is essential that they undergo a decontamination process before entering processing lines, and these methods should not compromise their bioactive properties. In this context a non-thermal technology, gamma irradiation, was used as a decontamination procedure. For this purpose, samples of Mentha piperita L. (peppermint) was irradiated using a 60Co experimental chamber, at the doses of 1, 5, and 10 kGy. The hydroethanolic extracts were then further evaluated through the virucidal efficacy assay, using two enteric viruses – human adenovirus type-5 (HAdV-5) and murine norovirus type-1 (MNV-1, as a human norovirus surrogate). The antibacterial activity was evaluated against a set of Gram-positive and Gram-negative bacteria. For the virucidal activity, data suggested that the irradiation treatment of all species can preserve the natural properties of the plant against enteric viral pathogens. The hydroethanolic extracts of peppermint reveal a low antibacterial potential for all the tested bacteria. However, antibacterial activity of gamma irradiated samples did not affect this bioactivity for none of the microbial agents tested. Validation of antimicrobial potential of medicinal plants, after gamma irradiation processing, are scarce in the literature. This study allowed defining the influence of this treatment on the bioactive properties of peppermint.
