Jeff Daelman

Microbiological Performance of a Food Safety Management System in a Food Service Operation

The microbiological performance of a food safety management system in a food service operation was measured using a microbiological assessment scheme as a vertical sampling plan throughout the production process, from raw materials to final product. The assessment scheme can give insight into the microbiological contamination and the variability of a production process and pinpoint bottlenecks in the food safety management system. Three production processes were evaluated: a high-risk sandwich production process (involving raw meat preparation), a medium-risk hot meal production process (starting from undercooked raw materials), and a low-risk hot meal production process (reheating in a bag). Microbial quality parameters, hygiene indicators, and relevant pathogens (Listeria monocytogenes, Salmonella, Bacillus cereus, and Escherichia coli O157) were in accordance with legal criteria and/or microbiological guidelines, suggesting that the food safety management system was effective. High levels of total aerobic bacteria (>3.9 log CFU/50 cm(2)) were noted occasionally on gloves of food handlers and on food contact surfaces, especially in high contamination areas (e.g., during handling of raw material, preparation room). Core control activities such as hand hygiene of personnel and cleaning and disinfection (especially in highly contaminated areas) were considered points of attention. The present sampling plan was used to produce an overall microbiological profile (snapshot) to validate the food safety management system in place.

Growth/no growth models for heat-treated psychrotrophic Bacillus cereus spores under cold storage

The microbiological safety of refrigerated and processed foods of extended durability (REPFED) is linked to spore-forming pathogens, more specifically Clostridium botulinum and Bacillus cereus. In this study two sets of growth/no growth (GNG) models are presented for the spores of two B. cereus strains. The models incorporate both product (water activity (a(w)) and pH) and process parameters (pasteurization value at 90 °C (P(90)) or heating temperature). The first model evaluates the effect of four different P(90)-values (P(90)=0, 4, 7 or 10 min, all applied at 90 °C) on the germination and subsequent growth of B. cereus spores under different conditions of pH and a(w) at 10 °C. These models show that a heat treatment not only increases the time to growth (TTG), but also significantly increases the minimal a(w) and pH necessary for germination and subsequent growth: e.g. at a(w) 0.995 and without heat treatment (P(90)=0), strain FF355 B. cereus spores were predicted to germinate and grow at pH 5.3. With a P(90) of 10 min, the minimal pH increased to 5.7. The second set of models for B. cereus spores compares the effect of three heat treatments with the same P(90)-value (10 min) but applied at different temperatures (85, 87 and 90 °C), on the germination and subsequent growth at 10 °C. The second model shows that lower heating temperatures (85 and 87 °C) had less effect on the TTG and minimal a(w) and pH than a higher temperature (90 °C). Finally, the first set of models was validated in broth using spores of seven psychrotrophic B. cereus strains, to evaluate the effect of strain variability on the model predictions. The results of the validation (% growth) were compared to the predicted growth probability. The results showed that the models were prone to fail-dangerous results (i.e. predicting no growth when growth was observed: 17%-34%). Using a very low threshold for growth (0.1% predicted chance of growth was considered to be complete growth), the models were more fail-safe (11%-34%) than fail-dangerous (0.4%-14%).

Exposure assessment of Malondialdehyde, 4-Hydroxy-2-(E)-Nonenal and 4-Hydroxy-2-(E)-Hexenal through specific foods available in Belgium

Malondialdehyde (MDA), 4-Hydroxy-2-(E)-Nonenal (HNE) and 4-Hydroxy-2-(E)-Hexenal (HHE) are reactive aldehydes found in foods and are formed due to decomposition of polyunsaturated fatty acid hydroperoxides. In the present study, sixteen food categories were analyzed for the aforementioned aldehydes and in combination with consumption data obtained from a national representative sample of the Belgian population, a quantitative exposure assessment was performed. MDA was detected above the detection limit in 84% of the analyzed samples while HNE and HHE in 63% and 16% of the samples respectively. Consumption of dry nuts, fried snacks, French fries and cured minced meat products were found to contribute the most to the intake of MDA and HNE. Intake of HHE from the foods analyzed was found not to be significant. An evaluation of any potential risk related to the intake of the studied aldehydes through the studied foods was performed by applying the threshold of toxicological concern concept. No risk to human health could be identified related to the consumption of these foods for the vast majority of the consumers, with the only exception of a small proportion (3.8%) of those who consume cured and minced raw meat, that could be at risk.

Assessment of the microbial safety and quality of cooked chilled foods and their production process.

Refrigerated processed foods of extended durability (REPFEDs) are a heterogeneous group of food products. This study assesses the microbial safety and quality along the production process in five REPFED companies. Samples were taken of raw materials (n=123), intermediate products (n=123), end products at production day (n=45) and at end of shelf life (n=90), food contact surfaces (n=226) and workers hands/gloves (n=92). Samples are analysed for total psychrotrophic aerobic count, aerobic spore count, sulphite reducing Clostridia, Bacillus cereus and Listeria monocytogenes. Both L. monocytogenes and B. cereus were detected on the raw materials. Nine of 72 raw materials tested were positive (in 25g) for L. monocytogenes and all but one of these raw materials were raw or minimally processed animal products. Three of 123 raw materials contained high counts (>4log CFU/g) of B. cereus, all of these samples were dried herbs. During production both food contact surfaces (90/226) and gloves (43/92) contained increased levels of total psychrotrophic aerobic counts (≥3log CFU/25cm(2)). This points out a potential source of bacterial recontamination. However, only a four and six of 223 food contact surfaces were positive (per 25cm(2)) for L. monocytogenes and B. cereus respectively. None of the gloves sampled contained L. monocytogenes and only 2 sets of gloves were positive for B. cereus. Of the 123 intermediate products tested twelve tested positive for L. monocytogenes (in 25g) and 5 showed elevated counts of B. cereus (ca. 2.5log CFU/g). Despite the presence of L. monocytogenes in the raw materials, the production area and in some of the intermediate products, none of the end products were positive for L. monocytogenes and only 9 of 135 samples (6.7%) showed to have low numbers of B. cereus (<2.7log CFU/g). This results show that the current pasteurization processes and the food safety management system are adequate to guarantee the production of microbiologically safe foods but that some improvements can still be made with regard to supplier selection, cleaning and disinfection, hygiene training and setting the shelf life duration.

Screening of different stress factors and development of growth/no growth models for Zygosaccharomyces rouxii in modified Sabouraud medium, mimicking intermediate moisture foods (IMF).

The microbial stability of intermediate moisture foods (IMF) is linked with the possible growth of osmophilic yeast and xerophilic moulds. As most of these products have a long shelf life the assessment of the microbial stability is often an important hurdle in product innovation. In this study a screening of several Zygosaccharomyces rouxii strains towards individual stress factors was performed and growth/no growth models were developed, incorporating a(w), pH, acetic acid and ethanol concentrations. These stress factors are important for sweet IMF such as chocolate fillings, ganache, marzipan, etc. A comparison was made between a logistic regression model with and without the incorporation of time as an explanatory variable. Next to the model development, a screening of the effect of chemical preservatives (sorbate and benzoate) was performed, in combination with relevant stress factors within the experimental design of the model. The results of the study showed that the influence of the investigated environmental stress factors on the growth/no growth boundary of Z. rouxii is the most significant in the first 30-40 days of incubation. Incorporating time as an explanatory variable in the model had the advantage that the growth/no growth boundary could be predicted at each time between 0 and 60 days of incubation at 22 °C. However, the growth/no growth boundary enlarged significantly leading to a less accurate prediction on the growth probability of Z. rouxii. The developed models can be a useful tool for product developers of sweet IMF. Screening with chemical preservatives revealed that benzoic acid was much less active towards Z. rouxii than sorbic acid or a mixture of both acids.

Strategies to increase the stability of intermediate moisture foods towards Zygosaccharomyces rouxii: the effect of temperature, ethanol, pH and water activity, with or without the influence of organic acids

Intermediate moisture foods (IMF) are in general microbiologically stable products. However, due to health concerns consumer demands are increasingly forcing producers to lower the fat, sugar and preservatives content, which impede the stability of the IMF products. One of the strategies to counteract these problems is the storage of IMF products at lower temperatures. Thorough knowledge on growth/no growth boundaries of Zygosaccharomyces rouxii in IMF products, also at different storage temperatures is an important tool for ensuring microbiologically stability. In this study, growth/no growth models for Z. rouxii, developed by Vermeulen et al. (2012) were further extended by incorporating the factor temperature. Three different data sets were build: (i) without organic acids, (ii) with acetic acid (10,000 ppm on product basis) and (iii) with sorbic acid (1500 ppm on product basis). For each of these data sets three different growth/no growth models were developed after 30, 60 and 90 days. The results show that the influence of temperature is only significant in the lower temperature range (8-15 °C). Also, the effect of pH is negligible (pH 5.0-6.2) unless organic acids are present. More specific, acetic acid had only an additive effect to ethanol and aw at low pH, whereas sorbic acid had also an additive effect at the higher pH values. For incubation periods longer than 30 days the growth/no growth boundary remained stable but enlarged gradually between day 60 and 90, except for the lower temperature range (<12 °C) where the boundary shifts to more stringent environmental conditions.

Development of a time-to-detect growth model for heat-treated Bacillus cereus spores

The microbiological safety and quality of Refrigerated Processed Foods of Extended Durability (REPFEDs) relies on a combination of mild heat treatment and refrigeration, sometimes in combination with other inhibitory agents that are ineffective when used alone. In this context, a predictive model describing the time-to-detect growth (measured by turbidimetry) of psychrotrophic Bacillus cereus spores submitted to various combinations of pH, water activity (aw), heat treatment and storage temperature was developed. As the inoculum was high, the time-to-detect growth was the sum of two times: for a large part of the spore lag time (time before germination and outgrowth) and to a lesser extent of the time to have subsequent vegetative cells growing up to a detectable level. A dataset of 434 combinations (of pH, aw, heat treatment, storage temperature and B. cereus strain), originally collected at Ghent University to build a growth/no-growth model for two Bacillus cereus strains, was re-interpreted as time-to-detect growth values. In the growth area (223 combinations) the time-to-detect growth was set as the longest time where none, or only one, of the 8 replicated wells showed growth. In the no-growth area (211 combinations) the time-to-detect growth was set as longer than the time where the experiment was stopped (60days or more) and analysed as a censored response. The factors of variation were heat-treatment intensity (85°C, 87°C and 90°C in a time range of 1 to 38min), storage temperature (8-30°C), pH (5.2-6.4) and aw (0.973-0.995). Two different strains were analysed. The model had a Gamma multiplicative structure; it was solved by Bayesian inference with informative prior distributions. To be implemented in a decision tool, for instance to calculate the process and formulation conditions required to achieve a given detection time, each Gamma term had some constraints: they had to be monotonous, continuous and algebraically simple mathematical functions (i.e. having analytical solution). Overall, the cumulative effect of various stressful conditions (pasteurisation process, low temperature, and low pH) enables to extend the time-to-detect growth up to 60days or more, whereas the heat-treatment on its own did not have a similar effect. For example, with the most heat resistant strain (strain 1, FF140), for a product at aw0.99, stored at 10°C, heat-treated at 90°C for 10min, a time-to-detect growth of 2days was expected when the pH equalled 6.5. Under the same conditions, if the pH was reduced to 5.8, the time-to-detect growth was predicted to be 11days (and 33days at pH5.5). After a pasteurisation at 90°C for 10min, for a product kept at 10°C, combinations of pH and aw such as pH6.0-aw0.97, pH5.7-aw0.98 or pH5.5-aw0.99 were predicted to extend the time-to-detect growth up to 30days. The developed model is a useful tool for REPFED producers to guarantee the safety of their products towards psychrotrophic B. cereus.