Develop, validate mathematical model describing growth of Pseudomonas spp. in raw poultry.

Poultry meat spoils quickly unless processed, stored and distributed under refrigerated conditions. Research has shown that the microbial spoilage rate is predominantly controlled by temperature. Moreover, the spoilage flora of refrigerated, aerobically stored poultry meat is generally dominated by Pseudomonas spp.

Scientists at Rutgers University wanted to develop and validate a mathematical model that predicts the growth of Pseudomonas in raw poultry stored under aerobic conditions over a variety of temperatures. They gathered information on 37 Pseudomonas growth rates from six previously published studies. Then the investigators developed a model relating the growth rate of Pseudomonas on poultry products to incubation temperature.

A square-root or Ratkowsky equation was used to model the data. The scientists compared the model predictions to 40 growth rate measurements collected in their laboratory. The growth rates were derived from more than 600 bacterial concentration measurements on raw poultry at 10 temperatures ranging from 0 C to 25 C.

The scientists visually inspected the data and the indices of bias and accuracy factors to analyze the performance of the model. The experimental data for Pseudomonas showed a 33% discrepancy with the predictions and a bias of +14%. Percent discrepancies were within the expected values reported in the literature, and positive bias factors demonstrate that the proposed model over-predicted the growth rate. For this reason, the scientists consider it fail-safe.

A properly constructed, validated, and applied model for Pseudomonas growth under aerobic conditions can provide a faster and cost-effective surrogate for challenge tests that estimate the effects of storage temperature on the shelf life of the product. The developed model allows end users--poultry processors--to determine the effects of both initial Pseudomonas concentrations and the storage temperature on the shelf life of poultry meat under aerobic storage conditions over temperatures from 0 C to 25 C.

Further information. Donald Schaffner, Food Science Department, 65 Dudley Rd., Cook College, Rutgers University, New Brunswick, NJ 08901; phone: [phone]; fax: [phone]; email: [e-mail].