Sensitivity of Listeria monocytogenes to rosemary ( Rosmarinus officinalis L.)

There are limited reports on antilisterial activities of spices and herbs in culture media and fewer still in foods. The present study was undertaken to identify spices that possess antilisterial properties and to evaluate effects in media and food. Of 18 spices screened on BHI agar (48 h, 35°C), only rosemary (≥0·5%, w/v) and cloves (≥1%, w/v) were listericidal. Tests were expanded with rosemary to include also its essential oil and four of the major oil constituents, oleoresin, encapsulated oil, and antioxidant extract of rosemary. Effects on Listeria monocytogenes strain Scott A in BHI broth were examined after 24 and 48 h at 35°C. The inhibitory concentrations of rosemary oil were 10 wl/100 ml broth. Of the major constituents of rosemary oil (cineole, borneole, α-pinene and camphor), only α-pinene (0·1 wl/100 ml) delayed listerial growth. The oleoresin, the encapsulated oil, and the antioxidant extract were also antilisterial (100 mg, ≥ 1 g and 0·02 g per 100 ml, respectively). The antilisterial activity of the aqueous extract of rosemary was considerably lower than that of the ground herb or the ethanolic extract. Addition of 0·5% finely ground rosemary or 1% rosemary oil to ready-to-eat pork liver sausage prior to cooking delayed listerial growth during refrigerated storage. The encapsulated oil (5%) and the antioxidant extract (0·3-0·5%) inhibited growth of listeriae, whereas the oil (1%) was ineffective.