Elsevier

Food Microbiology

Volume 93, February 2021, 103618
Food Microbiology

A predictive growth model for Clostridium botulinum during cooling of cooked uncured ground beef

https://doi.org/10.1016/j.fm.2020.103618Get rights and content

Highlights

  • We investigated the growth kinetics of Clostridium botulinum in beef.

  • Baranyi growth model was used to estimate the growth in beef.

  • A dynamic model to estimate growth was developed.

  • The model will assist the food industry to evaluate risk of Clostridium botulinum in beef.

Abstract

A dynamic model to predict the germination and outgrowth of Clostridium botulinum spores in cooked ground beef was presented. Raw ground beef was inoculated with a ten-strain C. botulinum spore cocktail to achieve approximately 2 log spores/g. The inoculated ground beef was vacuum packaged, cooked to 71 °C to heat shock the spores, cooled to below 10 °C, and incubated isothermally at temperatures from 10 to 46 °C. C. botulinum growth was quantified and fitted into the primary Baranyi Model. Secondary models were fitted to maximum specific growth rate and lag phase duration using Modified Ratkowsky equation (R2 0.96) and hyperbolic function (R2 0.94), respectively. Similar experiments were also performed under non-isothermal (cooling) conditions. Acceptable zone prediction (APZ) analysis was conducted on growth data collected over 3 linear cooling regimes from the current study. The model performance (prediction errors) for all 22 validation data points collected in the current work were within the APZ limits (−1.0 to +0.5 log CFU/g). Additionally, two other growth data sets of C. botulinum reported in the literature were also subjected to the APZ analysis. In these validations, 20/22 and 10/14 predictions fell within the APZ limits. The model presented in this work can be employed to predict C. botulinum spore germination and growth in cooked uncured beef under non-isothermal conditions. The beef industry processors and food service organizations can utilize this predictive microbial model for cooling deviations and temperature abused situations and in developing customized process schedules for cooked, uncured beef products.

Introduction

Clostridium botulinum is an anaerobic, gram-positive, spore-forming bacillus that produces a potent neurotoxin. The disease, botulism, caused by the neurotoxin is a serious public health concern. Spores of this pathogen can contaminate processed foods through dried agricultural products, raw materials, or may find their way into foods during processing and post-processing via the environment. Due to their high heat resistance and relatively high tolerance to environmental stresses, mild heat treatments aimed to retain organoleptic attributes of foods cannot eliminate spores of proteolytic C. botulinum type A and B. The presence of very low spore levels in food material can still result in spore germination, cell growth, and toxin formation that can produce symptoms of botulism (Juneja and Marks, 1999). Since the minimum growth temperature for proteolytic C. botulinum is 10 °C, spores surviving the cooking process can germinate, grow and produce the toxin if the rate of cooling after cooking is not adequate or if products are temperature abused during storage or during preparation and serving. While cooling deviations may occur due to electrical outage or equipment malfunction, mild temperature abuse scenarios can also occur during transportation or storage prior to consumption (Ecolab Inc., 2008).

Inadequate cooling and improper storage have been documented to be the major contributing factor in C. botulinum food poisoning outbreaks in low-acid foods (Bryan, 1978; Bean and Griffin, 1990; Aureli et al., 2000; Centers for Disease Control and Prevention, 2006; Townes et al., 1996; Trevejo, 1995). Foodborne botulism accounted for 39 (20%) botulism cases from seven states in 2015 and toxin type A accounted for 34 (87%) of the outbreaks (Centers for Disease Control and Prevention, 2015). A meat or poultry product was the food vehicle for 12.28% (7 out of 57 outbreaks) and 16.52% (37 out of 224 illnesses) of the foodborne botulism outbreaks and illnesses, respectively, in the United States, 2001–2017 (Centers for Disease Control and Prevention, 2019). Moreover, a meat product (i.e., beef chili) was the food vehicle for the second largest foodborne botulism outbreak (16 reported illnesses) in the United States from 2001 through 2017, which was most likely due to the temperature abuse of the product at a salvage store in Texas given the evidence (Centers for Disease Control and Prevention, 2019; Kalluri et al., 2003).

A proteolytic C. botulinum growth model capable of making predictions from 12 to 48 °C is currently available in the Pathogen Modeling Program (PMP) version 8 as well as in the online version of the PMP developed by U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS, 2018). This C. botulinum model has not been validated and moreover, data for fitting this model was collected in Reinforced Clostridial Medium, and not in food (Juneja and Marks, 1999). Because this is the only C. botulinum cooling model available at this time, USDA-Food Safety and Inspection Service does not object to the use of this model to determine compliance with the stabilization (cooling) performance standards as well as to determine the disposition of products subject to cooling deviations (U.S. Department of Agriculture, 2017). Specifically, FSIS recommends that establishments conduct modeling for C. botulinum when modeling for C. perfringens estimates >1.0-log growth, a common finding in cooling deviations. Therefore, the present study was conducted with an aim to fit and validate a dynamic model to predict the growth of C. botulinum from spores in beef at dynamic temperatures relevant to food processing operations. The model will assist the food industry and regulatory agencies in developing Hazard Analysis Critical Control Point (HACCP) plans as well as in determining compliance with the regulatory stabilization performance standards. Users of this models would be able to estimate the relative growth of C. botulinum from spores during the development of customized process schedules or during cooling deviations of cooked, uncured beef to determine if they meet the stabilization performance standards or agency policy of no growth of C. botulinum (mean net growth ≤0.30 log by modeling), which corresponds to a single multiplication cycle according to 9 CFR-Docket 95-033 F (Federal Register, 1999).

Section snippets

Strains and preparation of spore suspensions

Spores of five strains each of C. botulinum types A (56 A, 62 A, 69 A, 77 A, and 90 A) and proteolytic B (53 B, 113 B, 213 B, 13983 B, and Lamanna-okra B) used in the study were prepared as described previously (Christiansen et al., 1974; Tanaka et al., 1980). The spore crop of each strain was washed twice, suspended in sterile distilled water, and stored frozen at −80 °C until used. C. botulinum population densities for each spore suspension were determined using a five-tube

Results and discussion

The pH of the different batches of ground beef ranged was 5.85–6.09. This pH was recorded and not adjusted.

Declaration of competing interest

I confirm that.

  • 1)

    there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

  • 2)

    the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. I further confirm that the order of authors listed in the manuscript has been approved by all of us.

Acknowledgments

Funding for this study was provided by the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Current Research Information System (CRIS) project 8072-42000-079-00D through ARS National Program 108.

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