Residential Refrigerator Performance Based on Microbial Indicators of Ground Beef Preservation Assessed Using Predictive Microbiology Tools

Abstract

The aim of this study was to develop a refrigerator performance assessment procedure based on the temperature (2 × 106 values) of ground beef stored in its bottom drawer set to Fresh Meat (0 °C). Effects analyzed were ambient temperature (LT, 21.1 °C/HT, 32.2 °C), food load (LL, 22.5 kg/HL, 39.0 kg), door openings, and refrigerator compressor mode (SS, single speed/VS, variable speed). Published predictive microbiology models for exponential growth and ground beef temperature (48-h tests) were used to define absolute (API) and relative preservation indicators (RPI). For VS mode, API (log CFU/g) ranged from 1.7 (LT/LL) to 3.1 (HT/HL) for Listeria monocytogenes and 1.6 to 2.5 for Pseudomonas putida. Ground beef temperature reductions with minimum freezing risk yielded significantly lower API values indicating the need for refrigerator settings below 5 °C. Probabilistic analysis considering the model and temperature measurement variability confirmed this need. At 2 °C as recommended for ground beef storage, API2°C would be 1.1 (L. monocytogenes) and 1.4 logCFU/g (P. putida). RPI defined as the ratio of experimental API over API2°C yielded values > 1 confirming that a refrigerator control logic must consider preservation in addition to energy use compliance. In this study, SS outperformed energy-efficient VS compressors; however, compressor optimization considering energy use and food preservation would favor the latter. In conclusion, API and RPI values were effective tools to assess the microbial food preservation performance of a refrigerator and its use could be extended to analyze any segment of the refrigerated food distribution chain. Transforming time-temperature data into microbial performance indicators is practical and cost-effective.