Deterministic and probabilistic predictive microbiology-based indicator of the listeriosis and microbial spoilage risk of pasteurized milk stored in residential refrigerators

Following deterministic and probabilistic predictive microbiology procedures, cumulative 48 h exponential growth estimates were obtained for Listeria monocytogenes (Lm) and Pseudomonas putida (Pp) as preservation effectiveness indicators for pasteurized milk stored in the middle door shelf of a residential refrigerator set at 5 °C. Experimental factors studied were refrigerator load, door openings, compressor operating in variable (VS) or ON/OFF single speed (SS) mode, room temperature (T_Chamber = 32.2/21.1 °C), and milk exposure to T_Chamber (replicating product use). The 32.2 °C/high load condition yielded deterministic 48 h exponential growth estimates (ΔlogN_48h, log₁₀ N CFU/mL) of 1.6 ± 0.1/1.5 ± 0.1 for Lm and 5.0 ± 0.3/4.7 ± 0.3 for Pp (replicate-1/replicate-2, VS, milk kept in refrigerator). The corresponding 5–95% probabilistic ΔlogN_48h intervals were 1.0–2.3 and 3.4–6.6, respectively. Considering new technologies seeking to lower the temperature of products stored in door shelves, the analysis was repeated using simulated data obtained by lowering experimental temperatures by T_red (°C), a value determined for each test condition and keeping milk above 2 °C with 90% certainty. For the same previous conditions, deterministic ΔlogN_48h estimates for temperatures lowered by T_red= 4.5–4.8 °C, yielded ΔlogN_48h of 0.06 ± 0.0 for Lm and 2.6 ± 0.1 for Pp. These results highlight the importance of improving the temperature control of residential refrigerator door shelves.