The effect of γ-irradiation on chemical composition, microbial load and sensory properties of Sicilian oregano

Three samples of cultivated oregano, belonging to the most typical Sicilian species Origanum vulgare ssp. hirtum (Link) Béguinot (syn. Origanum heracleoticum L.), have been processed by γ-irradiation using two dose levels: 5 and 10 kGy. The irradiated and not-irradiated samples have been analyzed to quantify the essential oil content, microbial load, as well as for sensory properties. Fifty-three compounds, representing more than 98% of the total oil content have been fully characterized. All the cultivated samples showed a similar chemical profile composed of thymol and γ-terpinene as main compounds followed by p-cymene, α-terpinene, carvacrol and thymol methyl ethers, myrcene and carvacrol. The corresponding irradiated samples had different essential oil profiles with a reduction in monoterpene hydrocarbons and an increase of oxygenated monoterpenes. The microbiological results showed that the total bacterial and fungal counts decrease to less than 10 cfu/g when samples were exposed to the lowest irradiation dose. Among the irradiated and not-irradiated oregano samples, there were significant differences for all the descriptors except for bitter, pungent, astringent and hay flavour.