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 degrees 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 degrees C), and milk exposure toT(chamber) (replicating product use). The 32.2 degrees C/high load condition yielded deterministic 48 h exponential growth estimates (Delta logN(48h), log(10) 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 (replicate1/replicate-2, VS, milk kept in refrigerator). The corresponding 5-95% probabilistic Delta logN(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 (degrees C), a value determined for each test condition and keeping milk above 2 degrees C with 90% certainty. For the same previous conditions, deterministic Delta logN(48h) estimates for temperatures lowered by T-red= 4.5-4.8 degrees C, yielded Delta logN(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.