Growth of Pseudomonas fluorescens and Candida sake in homogenized mushrooms under modified atmosphere Original Research Article

Pseudomonas fluorescens and Candida sake were inoculated into mushrooms and stored under different gaseous atmospheres: air, CO2:N2:O2 (25:74:1%) and CO2:N2:O2 (50:49:1%). The growth of both microorganisms was measured during 18 days of storage at 5 and 10 °C. The percentages of O2 and CO2 inside the package and the pH of mushrooms were monitored during the storage. The maximum specific growth rate constant (μm), lag time (λ) and maximum population density (A) were evaluated from the modified Gompertz model using non-linear regression. The percentage of O2 in the samples stored in air decreased progressively during an 18-day storage while the percentage of CO2 increased. The pH of the samples stored under CO2 decreased whereas the pH of samples stored in air at 10 °C increased during the first 4 days followed by a decrease for the rest of the storage. The lag time increased with an increase in the percentage of CO2 in the atmosphere. The results suggest that the modified Gompertz model can be used successfully to describe the growth of both C. sake and P. fluorescens in mushrooms. Low CO2/high storage temperature combinations were found to favor the growth for both microorganisms.