Inhibition of fungal growth on bread by volatile components from spices and herbs, and the possible application in active packaging, with special emphasis on mustard essential oil

The effect of modified atmosphere packaging (MAP) on the most important spo ilage fungi of bread was investigated. Penicillium commune, P. roqueforti, Aspergillus flavus and Endomyces fibuliger were able to grow at oxygen leve ls down to 0.03%, while the chalk mould E. fibuliger was capable of growing even in the presence of an oxygen absorber. High levels of carbon dioxide retarded growth but not completely. As an alternative to MAP active packagi ng (AP) using volatile essential oils (EO) and oleoresins (OL) from spices and herbs were tested against a range of fungi commonly found on bread. Con centrations of 1, 10 or 100 mu l EO or OL were added to a filter paper plac ed in the lid of a Petri dish inoculated with one of the test fungi. The Pe tri dish was sealed hermetically to avoid the exchange of gases. Mustard es sential oil showed the strongest effect. Cinnamon, garlic and clove also ha d high activity, while oregano oleoresin only inhibited growth weakly. Vani lla showed no inhibitory effect towards the tested microorganisms at the ap plied concentrations. A. flavus was more resistant than the other microorga nisms while P. roqueforti was the most sensitive. Mustard essential oil was investigated in greater detail. The minimal inhibitory concentration (MIC) for the active component, allyl isothiocyanate (AITC), was determined for the same species and an additional three moulds and one yeast. MIC values r anged from 1.8 to 3.5 mu g/ml gas phase. Results showed that whether AITC w as fungistatic or fungicidal depended on its concentration, and the concent ration of spores. When the gas phase contained at least 3.5 mu g/ml, AITC w as fungicidal to all tested fungi. Results of sensory evaluation showed, th at hot-dog bread was more sensitive to AITC than rye bread. The minimal rec ognisable concentration of AITC was 2.4 mu g/ml gas phase for rye bread and between 1.8 and 3.5 mu g/ml gas phase for hot-dog bread. These findings sh owed that the required shelf-life of rye bread could be achieved by active packaging with AITC. Active packaging of hot-dog bread, may nevertheless re quire the additional effect of other preserving factors to avoid off-flavou r formation (C) 2000 Elsevier Science B.V. All rights reserved.