International Journal of Food Studies IJFS October 2015 Volume 4 pages 134–140

Teaching microbiological food safety through case studies

Florence Dubois-Brissonneta*,b, Laurent Guillierc, and Murielle Naıtalia

a AgroParisTech, Food Science & Technology dept, F-91300 Massy, Franceb INRA, UMR Micalis, F-91300 Massy, France

c Anses, French agency for food, environmental and occupational health and safety, F-94700, Maisons-Alfort*Corresponding author

florence.dubois-brissonnet@agroparistech.frTel: +33-1-69736472

Received: 29 June 2014; Published online: 18 October 2015Invited paper from the 3rd International ISEKI Food Conference - ISEKI Food 2014 - Bridging Training andResearch for Industry and the Wider Community - Food Science and Technology Excellence for a Sustainable

Bioeconomy

Abstract

Higher education students usually ask for more training based on case studies. This was addressedby designing a specific food safety module (24 hours) in which students were shown how to predictmicrobiological risks in food products i.e. they were asked to determine product shelf-life accordingto product formulation, preservation methods and consumption habits using predictive microbiologytools. Working groups of four students first identified the main microbiological hazards associatedwith a specific product. To perform this task, they were given several documents including guidesfor good hygiene practices, reviews on microbiological hazards in the food sector, flow sheets, etc. . .After three-hours of work, the working groups prepared and gave an oral presentation in front of theirclassmates and professors. This raised comments and discussion that allowed students to adjust theirconclusions before beginning the next step of their work. This second step consisted in the evaluationof the safety risk associated with the two major microbiological hazards of the product studied, usingpredictive microbiology. Students then attended a general lecture on the different tools of predictivemicrobiology and tutorials (6 hours) that made them familiar with the modelling of bacterial growth orinactivation. They applied these tools (9 hours) to predict the shelf-life of the studied product accordingto various scenarios of preservation (refrigeration, water activity, concentration of salt or acid, modifiedatmosphere, etc. . . ) and/or consumption procedures (cooking). The module was concluded by oralpresentations of each working group and included student evaluation (3 hours).

Keywords: Case studies; Food safety; Predictive microbiology

1 Introduction: Objectives of thetraining

These days, students prefer having less theo-retical lectures and more case studies that arerelevant to their future professional issues. Inthis context, an original food safety module (24hours) based on case studies was designed. Stu-dents were given one food product and were

asked to determine which mode of preservationwould be best and how long the associated shelf-life of this product should be. These questionswere professionally relevant as the determinationof shelf-life of food products is the responsibilityof manufacturers who increasingly employ pre-dictive microbiology tools. The proposed ap-proach was therefore relevant for the future ca-reer of students. While developing knowledge in

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microbiology, the overall objective of this modulewas to provide students with training that couldhelp them develop their ability to solve problemsand to take decisions.

2 Organization of the training

This food safety module is an optional module in-tended for engineering students (Year 4, secondyear in AgroParisTech) or master students (firstyear) interested in microbiological food safety.The prerequisite for attending this module wasto have general knowledge in both microbiologi-cal food quality and foodborne infections.The module included lectures, tutorials and ateam working case study. The latter was in-troduced through description of an example ofa recent outbreak that led to a shelf-life reduc-tion of the implicated product (French rillettes).Newspaper articles describing the crisis were firstanalysed by students and a discussion, initiatedby professors, led the students to identify theproblem and its origin, to propose solutions andto compare them to that selected by profession-als. The students were then split into groupsof 4 people for the case study. Working as ateam was part of the training. This taught stu-dents how to manage group dynamics, improvecommunication skills, and develop their abilityto raise questions. Each group identified the twomain microbiological hazards associated with aspecific food product, evaluated the microbialsafety risk associated with these hazards and de-termined the relevant shelf-life. A different foodproduct was taken on by each group. The stu-dents could choose the food product they wantto study among a list of products which hadbeen previously selected by professors for theirability to raise open-ended problems: more thanone solution could be proposed for their preserva-tion. Cooked ham, minced raw meat, fresh fish,poultry fillets, smoked salmon, packaged fresh-cut salad, zucchini puree and pasteurized milkwere some of the proposed products that couldbe studied. The diversity of the products allowedan exchange of information during oral presenta-tions and expanded the students’ body of knowl-edge.Professors supervised the module together with

a consultant from ANSES, the “French agencyfor food, environmental and occupational healthand safety”. This allowed aligning the moduleto both the food manufacturers’ concerns and tothe whole learning objectives of the training.

3 First issue: how can oneidentify and classify microbiologicalhazards in a food product?

This first part of the team project was de-signed to identify microbiological hazards in foodproducts. Students had in previous lectureslearned about the main foodborne pathogens,their growth pattern, survival rate and resis-tance characteristics, effects on human health,the routes of contamination, the potential in-criminated foods, the epidemiology and the ana-lytical methods. The knowledge acquired dur-ing lectures was applied and strengthened thestudents’ learning process. Professors gave eachgroup a file with a selection of scientific litera-ture, books, hygiene guidelines and regulationsthat could help analyse the product process andpotential microbiological hazards (spoilage mi-croorganisms, foodborne pathogens). Studentsdid not rely exclusively on the provided infor-mation and were encouraged to search for sup-plementary data in the university library, wherelibrarians together with professors helped themfind appropriate sources of information.While categorizing microbiological hazards, stu-dents also had to identify parameters that couldaffect microbial growth (temperature, atmo-sphere in packaging, salt concentration) in theirfood product and to select the most appropriateparameters for further studies. Students had sixhours to understand and evaluate information,articulate their thoughts and prepare a quick oralpresentation that included data projection us-ing slides. They presented their results of haz-ard identification and justified their prioritiza-tion. For example, Bacillus cereus (as sporeforming-bacteria) appeared as a relevant hazardin pasteurized products such as zucchini puree orpasteurized milk. Moreover, students were askedto propose various solutions to control the mainhazards and to state which scenarios of preser-vation should be chosen for the second part of

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the module. A discussion could take place withother students to exchange views on the selectedmodes of preservation. A first assessment of thegroup was done from this oral presentation.

4 Second issue: which scenarios ofpreservation can one choose andwhat is the correspondingshelf-life?

This part of the project intended to develop stu-dents’ ability to determine a product shelf-lifedepending on various scenarios of preservation.The shelf-life of a product can be selected by dif-ferent means that are listed in the annexe II ofthe European regulation (EC) n°2073/2005 (Itie-Hafez & Danan, 2014). In this training, the stu-dents employed predictive microbiology to pre-dict the growth or the inactivation of microor-ganisms in relation to their environment usingdifferent mathematical models, databases andsoftware (Delhalle, Daube, Adolphe, Crevecoeur,& Clinquart, 2012; Tenenhaus-Aziza & Ellouze,2015). So, students first attended a general lec-ture on predictive microbiology together with ad-ditional tutorials that helped students to betterunderstand the modelling and its limits and tomanipulate several tools of predictive microbiol-ogy (software, web-based resources). Afterwards,students applied these recently acquired skillsto determine shelf-life of their own products ac-cording to various scenarios they imagined. Therepetition of similar exercises, first in tutorialsand then with more freedom in the frameworkof a project, allowed students to reformulate thequestions, to appropriate and integrate the ap-proach and its implementation.

4.1 Tutorials to learn tools inpredictive microbiology

Six hours were dedicated to teaching differentmodels that are useful in food microbiology.First, microbial growth needs two types of mod-elling:

� Primary growth models give the growth ofthe microbial population as a function oftime (N=f(t)) in constant environmental

conditions. The adjustment of the mod-els to experimental data allows determina-tion of relevant parameters such as the du-ration of the lag phase (lag) and the maxi-mal specific growth rate (µmax). The mostcommon models were described and uti-lized, from the simplest exponential modelto more complex ones such as Gompertz, lo-gistic or Baranyi & Roberts models (Zwi-etering, Jongenburger, Rombouts, & Van’tRiet, 1990; Baranyi & Roberts, 1994; Rossoet al., 1996). In the tutorials, students com-pared results obtained from the adjustmentof different models when applied on a samedata set.

� Secondary growth models describe the evo-lution of µmax as a function of the envi-ronmental conditions such as temperature,CO2 concentration, etc (µmax=f(T, [CO2],. . . )). Polynomial, square root or cardi-nal models (Ratkowsky, Olley, Mcmeekin, &Ball, 1982; Rosso, Lobry, & Flandrois, 1993;McClure et al., 1994; Ross & Dalgaard,2004) were described and applied in tuto-rials to evaluate the shelf-life of apple com-pote under pre-defined conditions of storage.Students compared the value obtained withdifferent primary and secondary models tothose given by the free web-based resources,Combase (www.combase.cc) and PathogenModelling Program (pmp.errc.ars.usda.gov/PMPOnline.aspx). The divergence of the re-sults obtained and the impact on the choiceof the shelf-life was discussed in relation tothe type of hazard and its level. Studentswere often concerned by the wide range ofvalues obtained for the shelf-life dependingon the model utilized. This led them to be-gin to exercise a critical approach to results.

Secondly, students were taught how to use mod-els of bacterial inactivation, in order to predictthe impact of cooking for example. As for growthmodels, there are two types of inactivation mod-els:

� Primary inactivation models feature theevolution of a microbial population as afunction of time under constant environ-mental conditions (for example, at 100°C).

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Some models like log-linear model, biphasicor Weibull models (Geeraerd, Valdramidis,& Van Impe, 2005) were described and stu-dents could test them upon a provided dataset using GinaFit (Geeraerd et al., 2005), afreeware Add-in for Microsoft Excel software(cit.kuleuven.be/biotec/ginafit.php).

� Secondary inactivation models describe theimpact of environmental conditions upon in-activation parameters. Some common mod-els, like Bigelow or Mafart models (Couvert,Gaillard, Savy, Mafart, & Leguerinel, 2005)were described. In tutorials, students couldevaluate which parameter had the highestimpact on the logarithmic destruction of amicrobial population when several factorsvaried together. These models highlightedimportant microbial behaviour: for exam-ple, an increase of temperature appearedmore efficient than an increase of time toeradicate a given level of microorganisms.

4.2 Team work project: impact ofenvironmental parameters ongrowth rate

Back in their group and to their chosen foodproduct, students took possession of the mathe-matical tools and using databases, mainly Com-base (Baranyi & Tamplin, 2004), or data fromliterature. Students extracted some experimen-tal data of growth rate obtained in their foodproduct (which is rare) or mainly in culturemedium for the main microbiological hazardsthey had previously identified according to im-pacting environmental factors. They then ap-plied a relevant secondary model for determiningthe bacterial growth rate according to this fac-tor. For example, Figure 1 illustrates the growthrate modelling according to temperature for non-psychrotrophic strains of Bacillus cereus in cul-ture medium, as well as the cardinal tempera-tures. This was obtained using the Rosso’s model(Rosso et al., 1993) and data from literature(Carlin et al., 2013). Additionally, students usedthe few growth rates obtained from challenge-testexperiments carried out in the same food cat-egory as their studied product (for example B.

cereus in zucchini puree) to calibrate their mod-els and thus obtained more realistic predictions(Membre et al., 2005). Using other relevant mod-els and depending on the impacting parametersfor their product, students could determine theimpact of different formulations such as concen-trations of preservative such as salt (in connec-tion with water activity), acids, nitrites, etc. . .or of various atmospheres of packaging on thegrowth rate values.

4.3 Team work project:determination of the productshelf-life according toscenarios of preservation

Legislation stipulates that the shelf-life (that isthe manufacturer’s responsibility) must also pro-vide information regarding the expected stor-age conditions. The last student task thus con-sisted of definition and consideration of a vari-ety of plausible scenarios of preservation i.e. sev-eral phases of storage at different temperaturesor under different atmospheres (before and af-ter opening the packages). To do so, studentsintegrated supplementary data such as, in thecase of refrigerated products, the time spent incommercial and domestic fridges, the mean fridgetemperature and the variation of fridge tempera-ture, etc. . . using survey data (James, Evans, &James, 2008; Lagendijk, Assere, Derens, & Car-pentier, 2008).For example, pasteurized milk, which is supposedto be contaminated with 1 Bacillus cereus sporeper gram, can be stored 2 days at 4°C in the fac-tory, 2 days at 7°C at the retail and a few daysin the consumer’s fridge. The limit of hazardous-ness (105 bacteria/g) will be reached at differenttimes according to the fridge temperature andshelf-life can thus be calculated under these con-ditions (Figure 2). In this particular case, shelf-life can vary from 21 days at 7°C to only 6 daysat 12°C. This raised the students’ awareness ofthe importance of controlling the fridge temper-ature.Other factors were taken into account to deter-mine the shelf-life e.g. packaging under CO2, de-creased salt or nitrite concentrations for nutri-tional purposes. With the help of the devel-

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Figure 1: Growth rate of non-psychotropic strains of Bacillus cereus according to temperature. Exper-imental data were obtained from the literature (Carlin et al., 2013) and fitted using the Rosso’s model(Rosso, Lobry, & Flandrois, 1993)

Figure 2: Modelling of growth of a psychotropic Bacillus cereus during the different phases of storage(A) and number of days to reach 105 bacteria/g (B), according to the fridge temperature. The valuesof µmax at the different temperatures were obtained from a square root secondary predictive model andthen used in the primary predictive model of exponential growth without lag phase

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oped models, students could quantitatively ad-dress some practical questions: what is the con-sequence of using modified-atmosphere packag-ing on shelf-life, which concentration of lactateshould be added to the product to compensatefor the reduction of salt, what is the best cookingtime-temperature recommended to the consumerto minimise bacterial risks, what is the increaseof shelf-life obtained thanks to the use of a bio-preservation microflora?Finally, students had to establish a rational shelf-life based on the available information and onforeseen uncertainties. They had to justify theirchoice with safety concerns but also with perfor-mance and cost concerns. They were asked toestablish a safety margin from these data and totake into account the consumer understanding ofthe label “use by date”. They learned to reviewand organize information depending on their pri-orities and to develop skills that can be appliedto solve various problems.Students had 9 hours to work on the second is-sue of their case and this included creating thescenarios, choosing the most demonstrative ones,and preparing the final oral presentation. Af-ter presentation of the various scenarios and therespective associated shelf-life, discussion couldtake place between students and professors aboutthe choice of the best way to preserve the prod-uct. The final assessment of the group was donefrom this oral presentation.

5 Conclusions

This module provided progressive guidance in or-der to make students familiar with predictive mi-crobiology. It made students more aware of boththeir available knowledge and the additional in-formation they needed to find to propose a solu-tion for the product preservation. They becameaware of how and in which proportion each envi-ronmental parameter could impact the product’sshelf-life.Along this module, students’ skills such asproblem-solving and decision-making were devel-oped. It also promoted students’ self-confidencein their ability to propose solutions. They ac-quired knowledge but also know-how and know-be through an active, integrated and construc-

tive process. Globally, this type of pedagogydeveloped students’ interest in the subject mat-ter, here predictive microbiology, and helped stu-dents to become self-directed learners. The in-crease in students’ motivation could be assessedthrough the high demand for this course whichwas very well evaluated by the students.

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