Methodology for the food preservation assessment of residential refrigerators: Compressor and consumer practices effects on absolute and relative preservation indicators

Predictive microbiology models and 2.8E6 ham temperature measurements quantified absolute (API) and relative preservation indicators (RPI) assessing the performance of a residential refrigerator operating at 5 °C, the conventional setting for energy use assessments. Factors considered were compressor (single/variable speed, SS/VS), ambient temperature (21.1/32.2 °C), food load (22.5/39 kg), doors (closed/opening cycles), and fixed/movable samples (simulating breakfast use). APIT(t) based on 48 h temperature-dependent Listeria monocytogenes exponential growth ranged 0.23–0.36 log CFU/g at 32.2 °C/VS for all sample types and loads. The API value at the recommended 5 °C for ham (API5 °C, 0.155 log CFU/g) defined RPI = APIT(t)/API5 °C with values <1, ~1, >1 indicating a better, similar or worse preservation than constant 5 °C storage. The highest RPI value (2.32) was observed for VS/32.2 °C/high load/movable samples; however, it reached 1.10 when the entire ham temperature profile was lowered by 3.7 °C, the maximum possible without risking product freezing. A probabilistic analysis considering the variability of predictive microbiology parameters and temperature measurements, yielded high 95% percentile RPI values for all conditions. Although the SS compressor showed better RPIs, operating strategies for all compressor types should be modified to ensure lower-temperatures and shorter temperature recovery times while still meeting energy use regulations. The higher energy efficiency and multiple adjustments possible of VS compressors suggest that they should deliver better food preservation than SS compressors. This study showed an effective use of product temperature to assess the preservation performance of all cold chain components.