Use of Antimycotics, Modified Atmospheres, and Packaging to Affect Mold Spoilage in Dairy Products

The effects of natamycin, oxygen scavengers and a 25% CO₂:75% N₂ modified atmosphere on the growth of Penicillium roqueforti in shredded cheddar and mozzarella cheese stored at 10°C for 0, 60, 120, or 180 day was studied. Microbiological and sensory testing was assessed on 0, 7, 14 and 21 days after opening. Carbon dioxide decreased (P<0.05) as O₂ (P>0.05) and N₂ (P>0.05) increased throughout storage. Cheddar and mozzarella cheeses were stored for 180 and 60 days, respectively without significant (P> 0.05) increases in yeast and mold populations. Fungal populations increased significantly (P< 0.05) after packages were opened. Differences in yeast and mold (YM) counts during storage and once the packages were opened were independent of natamycin application and presence, O₂ scavengers and inoculated Penicillium roqueforti for both types of cheeses.

Growth of Penicillium roqueforti, Aspergillus niger, Geotrichum candidum and Neosartorya fischeri were evaluated in atmospheres of 0:30:70, 0.5:29.5:70, 1:29:70, 2:28:70, and 5:25:70, O₂:CO₂:N₂ over a 5-day period. Spores were cultured on antibiotic-supplemented potato dextrose agar (pH 5.6, a_w 0.95) and incubated at 25°C. All four molds germinated and grew at 0.5:29.5:70. Extent of mycelia growth diameter (mm) increased significantly (P<0.05) as oxygen concentration increased from 0.5% to 5%. All growth was inhibited at 0:30:70, but germination and growth occurred once cultures were exposed to 20.9% atmospheric O₂, indicating that a modified atmosphere containing no residual O₂ is fungistatic.

Yeast and mold growth was seen in ultra-pasteurized (UP) extended shelf-life fluid milk stored at (7.2°C). Ten half-pint, pint, quart and half gallon filled cartons were randomly selected from all UP products available. Samples, pulled at random on day 0, 15, 30, 45, and 60, were plated on Yeast and Mold Petrifilm™. Forty-seven percent of the UP products stored for 45 days tested positive for mold. Fungal growth was apparent down the side and along the bottom of the 5th panel. Contamination was traced to the presence of yeast and mold spores in paperboard cartons. Pinholes were present in the polyethylene coating and wicking occurred at the unskived 5th panel. Fungi of similar origin and fatty acid profile were isolated from UP milk products and the paperboard cartons.