Inhibition of fungal growth with extreme low oxygen levels

Fungal spoilage of foods is effectively controlled by removal of oxygen from the package, especially if this is combined with elevated carbon dioxide (CO2) levels. However, great uncertainty exist on just how low the residual oxygen levels in the package must be especially when carbon dioxide levels are low. This is especially interesting as high levels of CO2 may have a deleterious effect on the sensorial properties of the product.The objective was to determine the effect of very low oxygen levels (less than 1%) on growth and secondary metabolite production by the most common fungal contaminants of a wide range of products, and to determine the limit of growthFungi isolated from a wide range of products were incubated for up to three weeks at 25oC , 90% relative humidity at 1.0, 0.5, 0.25, 0.1, and 0.05% oxygen respectively in a custom made incubator with an interlock system for sequential removal of samples. Fungal metabolites were detected by High Pressure Liquid Chromatography (HPLC).All fungi were unaffected by reduction of oxygen levels to 1.0%, whereas already at 0.5% growth of the fruit spoilage fungi Alternaria infectoria and Botrytis cineria were reduced by 25%. Most Penicillia and Aspergilli were also inhibited by oxygen levels less than 0.5%, but less than 0.01% was required to efficiently inhibit these fungi. Most resistant to very low oxygen levels was the Fusarium species.These results shows that very low oxygen levels are required to avoid fungal growth in package food with low CO2 levels. Active packaging with oxygen absorbers may be considered for these products. The packaging solution must also reflect the micro flora of the product.