INHIBITION OF PSEUDOMONADS IN COTTAGE CHEESE BY PACKAGING IN ATMOSPHERES CONTAINING CARBON-DIOXIDE

Packaging of creamed-style cottage cheese, pH 4.9, in an atmosphere of 40% (v/v) CO2 inhibited the growth at 5 or 15°C of pseudomonads inoculated into the cheese. Increases of up to 3 weeks in the time taken to reach a count of 106 colony-forming units of Pseudomonas g-1 of cottage cheese were observed under some conditions. Addition of CO2 throughout the cheese before packaging was necessary to inhibit pseudomonads both at the surface and in the depth of the cheese. The principal effect of CO2 on the growth of the pseudomonads was a substantial increase in the lag times, but growth rates also decreased. Inhibition was greatest when low levels of pseudomonads were present initially. Inhibition by CO2 was greater at 5°C than at 15°C and greater at the surface than in the depth of the cheese. The flavor and pH of the cheese were not affected by the CO2. Growth of Listeria monocytogenes inoculated into cottage cheese was not observed in containers packaged in air or 40% CO2. © 1993 Academic Press Limited.