Modified atmosphere packaging and gamma-irradiation of some herbs and spices: Effects on antioxidant and antimicrobial properties

Thyme, rosemary, black pepper, and cumin were packaged in 100% N₂ (MAP) or air (AP) and gamma-irradiated at 0, 6, or 14 kGy. The changes in antioxidant and antimicrobial activities of their essential oils and methanol extracts were determined. Irradiation decreased the total phenolic content of AP samples (except thyme). Irradiation increased the 2,2-diphenyl-2-picrylhydrazyl radical scavenging activity in thyme extract and cumin essential oil in AP, but it decreased the activity in cumin extract (MAP). Ferric reducing antioxidant power was increased in rosemary (MAP) and thyme (MAP and AP) essential oils and rosemary (MAP and AP) and black pepper (AP) extracts, whereas it was decreased in the thyme extract (MAP) by irradiation. Irradiation increased the β-carotene-linoleic acid bleaching based antioxidant activity in essential oils of thyme (AP) and black pepper (MAP), but it decreased the activity in cumin extract (MAP). Irradiation increased antimicrobial activities of thyme and cumin essential oils. Practical applications: Gamma-irradiation is frequently used in sterilization of herbs and spices, but it may affect some of their quality attributes. The irradiation-induced changes in the quality depend on atmosphere (especially on O₂ level) during the treatment and thus can be controlled by modified atmosphere packaging (MAP). The effects of the combination of gamma-irradiation and MAP on antioxidant and antimicrobial properties of thyme, rosemary, black pepper and cumin are evaluated. Irradiation had an enhancing effect on the antioxidant and antimicrobial properties of the samples in most cases and can be applied under O₂-free modified atmospheres.