Nisin synergy with natural antioxidant extracts of the herb rosemary.

摘要

Nisin (a bacteriocin) is active against both food spoilage and foodborne pathogenic Gram-positive bacteria. Previous studies have demonstrated that nisin activity can be enhanced in combination with chelating agents, certain emulsifiers, and essential oils of herbs. Such combined food protection solutions offer the benefits of a multiple hurdle system, which gives better prevention of the emergence of less sensitive organisms and which may also reduce the required dosage of a single preservative. The present study examined the combination of nisin with natural extracts of rosemary (Rosmarinus officinalis), which contain high levels of antioxidant phenolic diterpenes and low levels of flavour compounds, such as essential oils. In vitro testing showed such a combination to be synergistic. The rosemary extracts enhanced both the cidal and static inhibitory activities of nisin against Gram-positive bacteria. Comparative testing with differently processed extracts identified the phenolic diterpenes, carnosol and carnosic acid, as the primary synergists. The synergism was demonstrated against Listeria monocytogenes and Bacillus cereus in vitro and in chilled, pasteurized food models (chicken soup, meat and cheese pasta sauces). The effect was increased by low temperature and acid conditions..