Distributions of Microorganisms in Foods and Their Impact on Food Safety

Distributions of microorganisms in foods and their impact on food safety Ida Jongenburger Thesis committee Thesis supervisors Prof. dr. ir. M.H. Zwietering Professor of Food Microbiology Wageningen University Prof. dr. L.G.M. Gorris Professor of Food Microbiology Wageningen University Thesis co-supervisor Dr. ir. M.W. Reij Lecturer at the Laboratory of Food Microbiology Wageningen University Other members Prof. dr. H.C. Boshuizen, Wageningen University Prof. F. Butler, University College Dublin, Dublin, Ireland Prof. dr. ir. A.H. Havelaar, Utrecht University Dr. M.C. Spanjer, Food and Consumer Product Safety Authority, Utrecht This research was conducted under the auspices of the Graduate School of advanced studies in Food Technology, Agrobiotechnology, Nutrition and Health Sciences (VLAG) Distributions of microorganisms in foods and their impact on food safety Ida Jongenburger Thesis submittted in fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus Prof. dr. M.J. Kropff, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Friday March 2 2012 at 4 p.m. in the Aula. Ida Jongenburger Distributions of microorganisms in foods and their impact on food safety 208 pages Thesis Wageningen University, Wageningen, NL (2012) With references, with summaries in Dutch and English ISBN 978-94-6173-207-1 This thesis is dedicated to my parents, who showed me the way, the truth, and the life (John 14: 6a). P. Jongenburger (1924-2006) C. M. Jongenburger-Bezemer Contents Abstract 9 Chapter 1 Introduction 11 Chapter 2 Impact of microbial distributions on food safety 21 I. Factors influencing microbial distributions and modelling aspects Chapter 3 Impact of microbial distributions on food safety 45 II. Quantifying impacts on public health and sampling Chapter 4 Factors influencing the accuracy of the plating method used to 67 enumerate low numbers of viable microorganisms in foods Chapter 5 Random or systematic sampling to detect a localised microbial 89 contamination within a batch of food Chapter 6 Actual distribution of Cronobacter spp. in industrial batches of 109 powdered infant formula and consequences for performance of sampling strategies Chapter 7 Modelling homogeneous and heterogeneous microbial contaminations 131 within a powdered food product Chapter 8 General discussion 155 Chapter 9 References 183 Summary 193 Samenvatting 197 Acknowledgements 201 List of publications 203 Overview of completed training activities 205 Abstract The physical distributions of pathogens in foods influence the likelihood that a food product will cause illness, but knowledge about the physical distribution of microorganisms in foods and especially the heterogeneity therein is scarce. This Ph.D. research aims to increase the knowledge of microbial distributions in foods and therewith to provide better insights in their impact on public health and food safety management activities. The research covers both theoretical investigations and practical experiments, focusing on powdered infant formula (PIF) as a suitable model product and the opportunistic pathogen Cronobacter spp. as a relevant microorganism in the practical experiments. The impact of spatial distributions of microorganisms, like homogeneous or more clustered distributions, on public health was investigated. Infrequent high doses were shown to mainly determine the probability of illness and also to dominate the arithmetic mean (mean of the counts) expressing the level of microorganisms present. The distribution ofCronobacter spp. in two industrial batches of PIF (a recalled batch and a reference batch) was quantified in detail. Additionally, batches of PIF on lab scale with well-mixed and localised contaminations of Cronobacter sakazakii were enumerated. In the recalled batch, the sample units were taken in the course of the filling time and the results showed that Cronobacter spp. were heterogeneously distributed. On local-scale, clusters of cells varying between 3 and 560 cells per cluster were present sporadically. Discrete and continuous statistical distributions were compared to model the enumeration data of the industrial and laboratory scale batches. Batches with low counts including zeros were fitted best by the Poisson-Lognormal distribution and Negative Binomial distribution. According to criteria proposed to compare the suitability of statistical distributions to model microbial distributions in foods, these two distributions had already been selected to be the most suitable candidates. Furthermore, the performances of random and systematic sampling ware compared to detect a localised contamination in a batch of food. Our calculations showed that systematic sampling rather than random sampling improved the sampling performance. Moreover, taking many small sample units systematically increased the probability to detect the localised contamination. Another systematic sampling strategy evaluated was stratified random sampling. Using the enumeration data of the recalled batch, stratified random sampling appeared to improve the detection probability ofCronobacter spp. as compared to random sampling. 9 Generally, taking more and smaller sample units, while keeping the total sampling weight constant, improved the performance of the sampling plans. The insights obtained in this thesis are considered to be relevant to a wide variety of dry products and to an extent also to other structured foods. They should be of use to food business operators to improve sampling and testing to verify control of their operation as well as to assess compliance of final products with food safety standards and guidelines before marketing. The results may equally be useful to governmental bodies setting and enforcing food safety standards (such as microbiological criteria) and conducting microbiological risk assessment. 10 Chapter 1 Introduction 1 11 Chapter 1 1. Food safety Food borne illnesses are at best unpleasant but at worst they can be fatal. People expect the food that they eat to be safe and suitable for consumption (CAC, 2003). This expectation or trust can easily be harmed. For example in the melamine case in China in 2008, powdered infant formula was contaminated with melamine, an anorganic chemical, which was added to low quality milk to falsify the protein levels. Nearly 300,000 infants were affected, more than 50,000 infants were hospitalised and six deaths have been confirmed (WHO, 2008). As a result, it will take a long time before consumers will trust this food product again in China. The food industry has an important responsibility to deliver safe food products. At the same time, the industry can easily be damaged by an outbreak of foodborne illness. In Germany in May 2011, an outbreak of Escherichia coli O104:H4 (EHEC) started, involving an unusual enteroaggregative strain (EAggEC VTEC) that produced the verocytotoxin. After indications by health officials that cucumbers produced in Spain were the source of the EHEC infections, the cucumber industry across Europe was severely damaged. A couple of weeks later, not cucumbers but bean sprouts grown in Northern Germany were pointed at as the actual source, causing a major impact on this part of the industry. When the outbreak was over at the end of July, it had caused the illness of 4075 people and 50 deaths in 15 countries in Europe and North America (WHO, 2011). Besides a major impact on public health, outbreaks as these damage food industry, by loss of earnings, unemployment as well as damaged trade relationships between countries and consumer trust. Therefore, both public and private parties need to ensure that pathogenic microorganisms are prevented, eliminated, or controlled to acceptable levels in food products. According to Codex Alimentarius (CAC, 2003), food safety assures that food will not cause harm to the consumer when it is prepared and/or eaten according to its intended use. Depending on the health hazard and the conditions in which food products are expected to be handled and consumed, precautions taken by the food industry and guidelines given by the authorities are more or less stringent (ICMSF, 2002). For instance, the production and packaging process of cooked and sliced chicken fillet, being a ready-to- eat product, has to be more stringently controlled to prevent the presence of Salmonella spp., than the production and packaging process of raw chicken fillet, which according to instructions will need to be baked/cooked before consumption. Obviously, consumers and food professionals, that prepare foods for final consumption, have to ensure that 12 Introduction the baking/cooking is adequate and have to follow relevant labelling instructions on the food. Food safety, in this regard, is a shared responsibility of all stakeholders: farmers and growers, manufacturers and processors, food handlers and consumers, as well as 1 governmental authorities. Thus, the industry and government have established a range of food safety tools to ensure safe food products that need to be used across the farm to fork food supply chain. Some key tools used in the industry, help it to produce wholesome food through well-controlled procedures that avoid harmful contamination whilst also avoid excess food waste. The food industry uses the food safety management system HACCP, the hazard analysis critical control points system, which identifies, evaluates, and controls all significant hazards for a particular food product. The prerequisites

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