Modelling the effects of modified atmosphere onSalmonella typhimurium in packaged meat during storage in the refrigerator and at 12°C

Abstract

The effects of storage atmosphere and temperatures onSalmonella typhimurium and aerobic plate count (APC) in meat were studied. Experimental results were analysed by non-linear regression of modified-Gompertz and logistic equations to generate “best fit”. In the absence of CO2 in package (with air and 40% O2+60% N2), in the refrigerator and at 12°C,S. typhimurium had higher growth rate and reached to higher number, whereas the presence of CO2 from 40 to 100% reduced the number ofS. typhimurium by 0.2 to 1.6 logs unit in the refrigerator. CO2 dissolves in water to form carbonic acid which reduces pH of meat and bacterial cytoplasm. This would be reduced the bacteria or inhibited their growth. The effects of the modified atmospheres on microorganisms in meat seems to be responsible for the data obtained, together with a probable contribution from pH which in turns is likely to be influenced by the gas atmosphere. It is known that CO2 has a bacteriostatic effect. Parameters of non-linear modified-Gompertz and logistic models of theS. typhimurium and APC in meat stored at variaus atmospheres were matched in a satisfactory way. Both the modified-Gompertz and logistic models showed good fit to all curves as assessed using the root mean square error and the correlation coefficient between the experimental and predicted values.