Kansas Agricultural Experiment Station Research Reports

Volume 0 Issue 1 Cattleman's Day (1993-2014) Article 303

2001

Escherichia Coli O157:H7 risk assessment for production and cooking of restructured

M.T. Ortega-Valenzuela

H. Thippareddi

Randall K. Phebus

See next page for additional authors

Follow this and additional works at: https://newprairiepress.org/kaesrr

Part of the Other Animal Sciences Commons

Recommended Citation Ortega-Valenzuela, M.T.; Thippareddi, H.; Phebus, Randall K.; Marsden, James L.; and Kastner, Curtis L. (2001) "Escherichia Coli O157:H7 risk assessment for production and cooking of restructured beef steaks," Kansas Agricultural Experiment Station Research Reports: Vol. 0: Iss. 1. https://doi.org/10.4148/ 2378-5977.1706

This report is brought to you for free and open access by New Prairie Press. It has been accepted for inclusion in Kansas Agricultural Experiment Station Research Reports by an authorized administrator of New Prairie Press. Copyright 2001 Kansas State University Agricultural Experiment Station and Cooperative Extension Service. Contents of this publication may be freely reproduced for educational purposes. All other rights reserved. Brand names appearing in this publication are for product identification purposes only. No endorsement is intended, nor is criticism implied of similar products not mentioned. K-State Research and Extension is an equal opportunity provider and employer. Escherichia Coli O157:H7 risk assessment for production and cooking of restructured beef steaks

Abstract Distribution of Escherichia coli O157:H7 in restructured beef from artificially inoculated pieces and destruction of E. coli O157:H7 in restructured beef steaks prepared from artificially inoculated meat was evaluated following broiling and grilling. In Study I, longissimus dorsi trimmings were inoculated with fluorescently marked E. coli O157:H7 cells to microscopically identify bacterial distribution throughout restructured cross-sections. E. coli O157:H7 fluorescent density was observed along the glue lines where meat pieces were enzymatically attached. Study II quantified the level of E. coli O157:H7 throughout the entire thickness of restructured beef. Cross-sectional slices of core samples from the steaks showed that bacterial contamination was evenly distributed (ca. 106 CFU/g). Study III determined the extent of E. coli O157:H7 reduction achieved during cooking. Beef trimmings were inoculated to a level of 107 CFU/g and used to prepare restructured beef chubs. Restructured steaks of three thicknesses (0.5, 1.0, and 1.5 inches) were sliced from the chubs and cooked to one of six target internal temperatures (120, 130, 140, 150, 160, or 170°F) by commercial gas grill or oven broiler. Broiling was more effective than grilling, although E. coli O157:H7 survival decreased as endpoint temperatures increased incrementally. To achieve an adequate level of safety confidence, restructured steaks should be cooked in a manner similar to ; to an internal temperature of at least 160°F.

Keywords Cattlemen's Day, 2001; Kansas Agricultural Experiment Station contribution; no. 01-318-S; Report of progress (Kansas State University. Agricultural Experiment Station and Cooperative Extension Service); 873; Beef; E. coli O157:H7; Restructured beef steaks; Cooking

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 License.

Authors M.T. Ortega-Valenzuela, H. Thippareddi, Randall K. Phebus, James L. Marsden, and Curtis L. Kastner

This research report is available in Kansas Agricultural Experiment Station Research Reports: https://newprairiepress.org/kaesrr/vol0/iss1/303 Cattlemen’s Day 2001

ESCHERICHIA COLI O157:H7 RISK ASSESSMENT FOR PRODUCTION AND COOKING OF RESTRUCTURED BEEF STEAKS

M. T. Ortega-Valenzuela, R. K. Phebus, H. Thippareddi, J. L. Marsden, and C. L. Kastner

Summary Introduction

Distribution of Escherichia coli O157:H7 Meat restructuring using cold set binding in restructured beef from artificially inocu- technologies like fibrinogen and thrombin lated meat pieces and destruction of E. coli enzymes provide quality, economic, nutri- O157:H7 in restructured beef steaks prepared tional, and marketing advantages in meat from artificially inoculated meat was evalu- processing. Food poisoning outbreaks with ated following broiling and grilling. In Escherichia coli O157:H7 have frequently Study I, longissimus dorsi trimmings were been attributed to ground beef consumed inoculated with fluorescently marked E. coli after cooking that was insufficient to destroy O157:H7 cells to microscopically identify pathogens that were translocated from the bacterial distribution throughout restructured surface to the meat interior. Restructured steak cross-sections. E. coli O157:H7 fluo- steaks may be perceived as more like intact rescent density was observed along the glue muscle steaks than as ground beef. Because lines where meat pieces were enzymatically of this perception, restructured steaks may be attached. Study II quantified the level of E. cooked at temperatures inadequate to destroy coli O157:H7 throughout the entire thickness surface microbial contamination that may of restructured beef. Cross-sectional slices of have been carried to the interior of the core samples from the steaks showed that restructured product. The objectives of our bacterial contamination was evenly distrib- research were to determine the extent of E. uted (ca. 106 CFU/g). Study III determined coli O157:H7 translocation in restructured the extent of E. coli O157:H7 reduction beef and to determine adequate cooking achieved during cooking. Beef trimmings protocols to eliminate E. coli O157:H7 from were inoculated to a level of 107 CFU/g and their interior. used to prepare restructured beef chubs. Restructured steaks of three thicknesses (0.5, Experimental Procedures 1.0, and 1.5 inches) were sliced from the chubs and cooked to one of six target inter- Study I: nal temperatures (120, 130, 140, 150, 160, or Five strains of Escherichia coli O157:H7 170°F) by commercial gas grill or oven (USDA-FSIS 011-82, ATCC 43888, 43889, broiler. Broiling was more effective than 43890, and Eh 7-4) were grown and marked grilling, although E. coli O157:H7 survival using a fluorescent probe, live-cell nucleic decreased as endpoint temperatures acid stain. Longissimus dorsi beef trimmings increased incrementally. To achieve an were mist inoculated (ca. 7 log10 CFU/g) and adequate level of safety confidence, restruc- allowed to attach at 39°F for 1 hr. Thawed tured steaks should be cooked in a manner proportional parts of fibrinogen and similar to ground beef; to an internal temper- thrombin enzymes, were mixed with the ature of at least 160°F. longissimus dorsi trimmings for 90 sec and stuffed into perforated casings using an (Key Words: E. coli O157:H7, Restructured Aligned Grain System™. The formed meat Beef Steaks, Cooking.) was hung at 41°F for 10 hr for setting the meat pieces, and frozen for 1.5 hr to form a

42 surface crust to facilitate sample collection. negative by direct plating were qualitatively A sterile stainless steel coring device cou- evaluated following a modified USDA pled to an electric drill was used to core the method. Presumptive E. coli O157:H7 sample along the width of the cylindrical colonies were confirmed biochemically and meat piece. The cores were fixed in a mix- serologically. Three replications were per- ture of paraformaldehyde (2%) and formed for each study. glutaraldehyde (0.2%) in neutral buffer solution (pH 7) for 6 hr, sectioned and visu- Results and Discussion alized under a confocal laser microscope. Study I: Study II: Confocal laser scanning microscopy A strain of E. coli O157:H7 (USDA- revealed a high level of E. coli O157:H7 FSIS 011-82, rifampcin resistant) was mist contamination along cross-sections of the inoculated (ca. 7 log10 CFU/g) onto the restructured beef chub. The fluorescent surface of longissimus dorsi beef trimmings. bacteria present midway through the cylin- The restructuring procedure from Study I drical restructured meat piece shows that the was followed. The formed beef roll (crust restructuring process translocates surface frozen) was sampled as previously described contamination into the interior. at three different locations about 4 inches apart. The meat cores were aseptically sliced Study II: into cross-sectional strips of 0.8, 0.4, 0.4, E. coli O157:H7 was uniformly distrib- 0.4, and 0.8 inches. Each cross-sectional uted (P>0.05) across the diameter (5 individ- strip was plated onto TSA-rif and the E. coli ual cross sections) of the restructured beef O157:H7 population was reported. chub, indicating translocation of surface inoculated E. coli O157:H7 into the interior Study III: of the chubs during restructuring. Section 3, The inoculation and restructuring proce- corresponding to the geometric center of the dures from Study I were followed. The core, revealed a mean bacterial population of cylindrical restructured beef chub (2.8" inch 6.16 log10 CFU/g. This section would be the diameter) was sliced into steaks of 0.5, 1.0, coldest point during cooking. and 1.5 inch thickness. Steaks were ran- domly assigned to six target internal temper- Study III: ature groups (120, 130, 140, 150, 160, and Broiling steaks from restructured beef 170°F) and were cooked under a typical trimmings to endpoint temperatures of 120, kitchen oven broiling element set at 500°F, 130, 140, 150, 160, and 170°F resulted in E. or cooked using a commercial gas grill. coli O157:H7 reductions of 1.03, 1.94, 2.70, Steaks were flipped upon reaching the mid- 4.32, 6.27, and 6.08 log CFU/g, respectively, point between original and final temperature. when plated on PRSA (1 log = 90%, 4 log = Internal temperatures were constantly moni- 99.99% reduction). Greater reductions were tored using a type T thermocouple threaded obtained when a selective medium (MSA) through the steak edge to the steak’s geomet- was used for plating, indicating sub-lethal ric center. After reaching the target internal injury to E. coli O157:H7 cells during cook- temperature, steaks were removed from the ing. Cooking of thicker steaks (1.0 and 1.5 grill or broiler, placed in heat resistant bags inches) resulted in consistently larger reduc- and immersed in an ice bath. Steaks were tions in E. coli O157:H7 compared to the 0.5 blended in a sterile food processor and a 25 inch steaks. This probably was due to g sample stomached in peptone water to thicker steaks requiring longer cooking provide a 1:5 w/v dilution. Surviving E. coli times. The post-cook temperature rise was O157:H7 populations were enumerated on higher for 1.5-inch thick steaks (9 to 22°F) MacConkey Sorbitol Agar (MSA) and Phe- compared to steaks 1.0 and 0.5 inch thick (3 nol Red Sorbitol Agar (PRSA). PRSA agar to 8°F and 7 to 12°F for 0.5 and 1.0 inch provided an estimate of the level of ther- thick steaks, respectively). The additional mally injured cells that may not have been microbial destruction in thicker steaks due to detected on MSA agar. Samples testing longer cook times and higher post-cook

43 temperature rise results in a safer steak, consistent and uniform because steaks are compared to thinner steaks. heated from the top (broiling element). The surface of the holding grill is close to the Cooking restructured steaks on a gas grill oven temperature, resulting in larger reduc- to endpoint temperatures of 120, 130, 140, tions in E. coli O157:H7 populations. 150, 160, and 170°F resulted in E. coli O157:H7 reductions of 0.87, 1.16, 1.25, Grilling thicker steaks (1.0 and 1.5 2.62, 3.73, and 4.51 log CFU/g, respectively, inches) resulted in larger reductions of E. when plated on PRSA. These reductions coli O157:H7 compared 0.5 inch thick were greater when a selective medium steaks, probably due to the longer cook (MSA) was used for plating the samples, times and higher post-cook temperature rise. indicating a significant number of injured but As observed in oven broiling, the post-cook not killed E. coli O157:H7 cells. These temperature rise was greater in steaks of 1.0 reductions were lower than the reductions and 1.5 inches (1 to 16°F and 6 to 19°F). attained using oven broiling. This was prob- ably due to the commercial grill using higher This study incorporated the use of an ice temperatures and shorter cooking times to bath to rapidly halt destruction of bacteria reach target temperatures. after steaks were removed from the broiler, to provide more accurate information con- Initial studies indicated that some re- cerning microbial destruction achieved at the structured steaks curled during cooking, identified target internal temperatures. probably due to different fiber alignment However, even after transfer to the ice bath, than normal steaks. Use of cook weights (1 internal temperature of the steaks continued lb steel plates with a handle) minimized but to rise above the target temperatures by as did not eliminate the curling. Using commer- much as 4 to 29°F. In food service applica- cial grill systems can result in cold spots on tions, the finished product would not be steaks due to curling, and thus reduce micro- cooled. Therefore, internal temperatures bial destruction. In addition, when cooked would likely rise to higher endpoints and be on a grill, the top surface of the steak is maintained longer, thereby increasing margin exposed to near ambient temperatures. On the of safety in pathogen destruction. contrary, in oven broiling, the temperature is more

44