Inhibition of Fungal Growth on Wheat and Rye Bread by Modified Atmosphere Packaging and Active Packaging Using Volatile Mustard Essential Oil

Wheat and rye bread artificially inoculated with molds were packed in modified atmospheres of 0%, 50%, 75%, or 100% CO 2 balanced with N 2 , and 3 levels of residual O 2 , 1%, 0.03%, or <0.01%/O 2 ‐absorber, and stored for 30 to 35 d. Modified atmosphere packaging (MAP) was quantitatively more effective for rye bread because fewer mold species grew at elevated CO 2 . However, the major rye bread contaminant, Penicillium roqueforti , was the overall most CO 2 ‐resistant mold and only the use of O 2 ‐absorber could prevent growth of this species. On wheat bread, the most CO 2 ‐tolerant mold was Penicillium commune , growing in 99% CO 2 (with high residual O 2 ), and Aspergillus flavus was the mold species that grew at lowest O 2 in 75% CO 2 treatment. The spoilage yeast/“chalk mold” Endomyces fibuliger was less affected by the different O 2 levels than the true filamentous molds, and none of the tested MAP treatments could prevent growth, but lag‐phase was increased with O 2 ‐absorber on wheat bread and decreased with 1% residual O 2 on rye bread. Experiments with volatile mustard oil showed that A. flavus and Eurotium repens were the most mustard oil‐resistant species on wheat and rye bread, respectively. A combination strategy with MAP and mustard oil proved most optimal, and total inhibition was achieved with 2 μL mustard oil/rye bread slice and between 2 and 3 μL/wheat bread. Results indicated that the nature and surface area of the product influences effectiveness of active packaging with mustard oil.