Effect of fermentation and post-fermentation heating times and temperatures for controlling Shiga toxin-producing Escherichia coli in a dry-fermented-type sausage

Authors: Shane, Laura; Porto-Fett, Anna; Shoyer, Brad; PHEBUS, RANDALL - Kansas State University; THIPPAREDDI, HARSHAVARDHAN - University Of Nebraska; Hallowell, Ashley; MILLER, KELSEY - Ursinus College; FOSTER-BEY, LIANNA - Ursinus College; CAMPANO, STEPHEN - Hawkins, Inc; TAORIMINA, PETER - John Morrell Food Group; GLOWSKI, DANIEL - John Morrell Food Group; TOMPKIN, ROBERT - Retired Non ARS Employee; Luchansky, John

Submitted to: Italian Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2018
Publication Date: 7/3/2018
Citation: Shane, L.E., Porto Fett, A.C., Shoyer, B.A., Phebus, R.K., Thippareddi, H., Hallowell, A.M., Miller, K., Foster-Bey, L., Campano, S.G., Taorimina, P., Glowski, D., Tompkin, R.B., Luchansky, J.B. 2018. Effect of fermentation and post-fermentation heating times and temperatures for controlling Shiga toxin-producing Escherichia coli in a dry-fermented-type sausage. Italian Journal of Food Safety. https://doi.org/10.4081/ijfs.2018.7250.
DOI: https://doi.org/10.4081/ijfs.2018.7250

Interpretive Summary: Over the past thirty years illnesses caused by serotype O157:H7 strains of Shiga toxin-producing Escherichia coli (STEC) have been frequently linked to undercooked and/or underprocessed beef products. Serotype O157:H7 strains have been considered an adulterant in raw ground beef and non-intact beef since 1994 and 1999, respectively. More recently, an additional six serotypes of STEC have also been declared adulterants if present in raw ground and non-intact beef due to their elevated potential for also causing human illness. Fermented products are generally safe due to their lower pH, processing conditions, and ingredients/composition, but on occasion such products may not be cooked, appropriately dried/held, and/or properly stored/handled following fermentation. This, in turn, may provide an environment in which E. coli O157:H7, as well as non-O157 STEC, may persist and survive, and possibly cause illness. Although fermentation has been practiced for centuries to preserve a variety of foods, including meats, fermentation and drying of dry-fermented sausage alone is only effective at killing about 100 cells of STEC per gram of product. Therefore, post-fermentation treatments, such as cooking or drying, are required to achieve the USDA Food Safety and Inspection Service (FSIS) mandate to eliminate up to 100,000 per gram of product. For these reasons we quantified the fate of a single strain each of serotypes O26, O103, O45, O111, O121, O145, O104, and O157 during fermentation and cooking of a pepperoni–type sausage. The results showed that fermentation to pH 4.6 or pH 5.2 delivered about a 5-log reduction in pathogen levels following post-fermentation cooking for 1 to 10 hours at 110 to 130F. These data will be useful for manufacturers of dry-fermented sausages to validate/achieve the required reduction of STEC while producing a high-quality and wholesome product. These data also confirm that processes previously validated as effective for serotype O157:H7 strains of E. coli will likely be as effective towards strains of the other six regulated serotypes of Shiga toxin-producing E. coli.

Technical Abstract: We evaluated typical fermentation and cooking time and temperature parameters for lethality towards of Shiga toxin-producing Escherichia coli (STEC) in a pepperoni-like, dry-fermented sausage. Coarse ground meat (25:75% beef:pork and 30:70% fat:lean) was purchased from a local vendor. The meat was mixed with a dry spice mix (3.69%), cure salt (3.60%), and a commercial starter culture (0.0188%; Pediococcus acidilactici) and inoculated with an 8-strain STEC cocktail (ca. 7.0 log CFU/g) comprised of single strains of serotype O157:H7, O104:H4, O26:H11, O45:H2, O103:H2, O111:H-, O121:H19, and O145:NM. Next, the batter was fine ground (3/16” grinding plate), stuffed into a 55-mm fibrous casing, and subsequently fermented at 96°F (35.6C) and ca. 85% relative humidity to a final target pH of pH 4.6 or pH 5.2. After fermentation, the pepperoni-like sausages were cooked to target internal temperatures of 100F (37.8C), 110F (43.4C), 120F (48.9C), and 130F (54.4C) and held for 0.5 to 12.5 h. In each of two to four trials, three chubs were analyzed at each sampling interval for each treatment tested. Regardless of the cooking temperature, after fermentation to a target pH of pH 4.6 or pH 5.2, the endpoint pH ranged from ca. pH 4.5 to pH 4.7 and ca. pH 4.8 to pH 5.1, respectively; following cooking pH decreased to ca. pH 4.0 to pH 4.4. When sausages were fermented to pH 4.6 or pH 5.2 and then cooked to 100° to 130°F and held for 0.5 to 12.5 h, water activity of sausages ranged from 0.934 to 0.951. Regardless of the target endpoint pH, fermentation alone delivered a 0.33- to 1.58-log CFU/g reduction in pathogen numbers. However, sausages fermented to pH 4.6 required less time to achieve appreciable reductions of the STEC cocktail than otherwise similar sausages that were fermented to pH 5.2. Fermentation to ca. pH 4.6 followed by post-fermentation cooking to 100, 110, 120, or 130F and holding for 0.5 to 12.5 h generated reductions of ca. 1.0 to 2.4, 0.9 to 5.2, 1.6 to 6.5, and 0.9 to 6.7 log CFU/g, respectively. Likewise, fermentation to ca. pH 5.2 followed by post-fermentation cooking to 100, 110, 120, or 130F and holding for 1 to 12.5 h generated reductions of 0.3 to 1.4, 1.2 to 6.8, 0.5 to 6.5, and 1.0 to 6.7 log CFU/g, respectively. Thus, the endpoint fermentation pH levels and post-fermentation cooking times/temperatures validated herein provide manufacturers with additional options to ensure product safety.