VALIDATION OF THE EFFECT OF INTERVENTIONS AND PROCESSES ON PERSISTENCE OF PATHOGENS ON FOODS
Location: Food Safety and Intervention Technologies
Title: Effect of storage and subsequent re-heating on viability of Listeria monocytogenes on pork scrapple
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 30, 2009
Publication Date: December 1, 2009
Citation: Adekunle, A.O., Porto Fett, A.C., Call, J.E., Shoyer, B.A., Gartner, K., Tuft, L., Luchansky, J.B. 2009. Effect of storage and subsequent re-heating on viability of Listeria monocytogenes on pork scrapple. Journal of Food Protection. 72(12):2530-2537.
Interpretive Summary: Listeria monocytogenes, a pathogen commonly associated with foods, can cause severe human illness. Unlike other food borne pathogens, L. monocytogenes can grow on a variety of ready-to-eat meats even if stored in the refrigerator. Scrapple is a very popular ready-to-eat (RTE) “savory mush”, typically made from pork trimmings, cornmeal, and different types of flour, such as wheat, whole wheat, or buckwheat, developed by Dutch settlers more than 200 years ago that is eaten primarily in the middle-Atlantic states of the United States. Relatively little is known as to whether or not scrapple would support growth of pathogens such as L. monocytogenes during refrigerated storage and/or whether or not re-heating scrapple just prior to consumption, as preferred/practiced by most consumers, would be effective at killing any cells of this bacterium that may on relatively rare occasion be present. In fact, our data revealed for the first time that pork scrapple does provide a very favorable environment for growth of L. monocytogenes. The bacterium grew from an inoculated starting level of about 100 cells per gram of scrapple to about 1,000,000 cells per gram within 33 days in the refrigerator. Perhaps more importantly though, re-heating scrapple on an electric skillet using times/temperatures stated on the product label and/or practiced by consumers as learned through our informal survey, was sufficient to reduce pathogen levels by 100 to 1,000,000 cells per gram. These data highlight the importance of Good Manufacturing Practices (GMP) and proper storage, handling, and/or reheating of scrapple to ensure that L. monocytogenes is not present on the finished product.
We evaluated the fate of Listeria monocytogenes on pork scrapple, a regionally-popular, ready-to-eat (RTE) meat product, both during storage and following re-heating. We also conducted an informal survey to address consumer practices for storing and re-heating scrapple. Regarding the survey, of some 129 consumers who responded to at least one of 8 questions, about half of the respondents (46.4%; 52 of 112) considered scrapple as RTE, the majority (69.7%; 76 of 109) stored it in the refrigerator, typically for 2 to 60 days before eating, and all respondents (100%; 112 of 112) preferred to reheat it prior to consumption, with most respondents (83.9%; 94 of 112) re-heating scrapple by pan frying it for 5 to 10 minutes at a medium to high temperature setting. Regarding pathogen behavior on scrapple, in each of three trials, slices (ca. 5.5 cm wide x 6.0 cm long x 1.0 cm thick; ca. 50 g each) of commercial pork scrapple were surface inoculated on both the top and bottom faces of each slice to a target level of ca. 2.0 log CFU/g with a five-strain cocktail of L. monocytogenes and placed into nylon-polyethylene bags that were vacuum-sealed and held at 4, 10°, and 21C for 60, 21, and 9 days, respectively. Pathogen levels increased from ca. 2.0 log CFU/g to 8.9, 9.5, and 9.9 log CFU/g after 44 (4C), 21 (10C), and 5 (21C) days, respectively. For the re-heating portion of this study, scrapple was cut into thicknesses of 1.3 cm (ca. 55 g) and 1.9 cm (ca. 85 g). The slices were inoculated on both the top and bottom faces and on all four sides with the same five-strain cocktail of L. monocytogenes to a target level of ca. 7.0 log CFU/g, and were then stored for 24 to 72 h at 4C to allow for attachment of L. monocytogenes cells to the meat. Next, the slices were reheated in a skillet (191C) for 0.5 min to 4 min per side or were reheated to target instantaneous internal temperatures ranging from 48.9 to 71.1C. For both the 1.3 cm and 1.9 cm thick slices, when reheated for 4 minutes per side, ca. a 6.5- and 2.3-log reduction of L. monocytogenes was observed, respectively. When re-heating to 48.9 or 71.1C, ca. a 2.6- to 5.2-log reduction (1.3 cm) and ca. a 2.2- to 4.2-log reduction (1.9 cm) were observed. These data confirm that in the unlikely event of post-process contamination of pork scrapple by L. monocytogenes, proper re-heating can appreciably reduce levels of the pathogen just prior to consumption.