Search

Predictive microbiology aims to evaluate the effect of processing, distribution, and storage operations on microbiological food safety. It is based upon the premise that the response of population of microorganisms to environmental factors are reproducible, and that, by characterizing the environment in terms of identifiable, dominant factors controlling growth responses, it is possible, from past observations, to predict the responses of those microorganisms in other, similar environments. Predictive microbiology models represent the microbial responses to the environment. They are based mainly on observations made in synthetic culture media. Models cannot take into account all factors that may affect the microbial growth but select the most influential factors and only model their effects. The main assumptions of predictive microbiology and risk analysis are discussed in the present chapter. Moreover, the classification of predictive models and application in dairy processing are given. Finally, a case study using the tertiary model Sym’Previus software is presented.

The aim of this study was to determine the survival kinetics of Salmonella enterica subsp. enterica in ripened raw milk cheese. Cheese samples inoculated with S. enterica subsp. enterica were stored at 5, 15 and 25 °C and analysed in terms of physico‐chemical and microbiological characteristics. Three primary models were used to estimate the kinetic parameters of S. enterica subsp. enterica. The secondary Arrhenius model was used to establish the relationship between temperature and parameter α of the Weibull model. Additionally, prediction of S. enterica subsp. enterica survival as a function of storage temperature was made. S. enterica subsp. enterica growth was inhibited during storage, and bacteria survived for an extensive period of time at high number (60 day at 5 °C, 26 day at 25 °C). The storage temperature significantly influenced the inactivation rate of Salmonella in raw milk ripened cheese and proceeded faster at 25 °C compared to remaining storage temperature. Obtained results suggest that contamination by Salmonella in raw milk cheese might result in residual risk.

BACKGROUND The Polish market for tvarog (curd cheese)-based products is growing continuously. The as- sortment of these goods include products with different textures, different additives and different flavours. In developing a successful food product one should ensure consumers are sufficiently involved during the development stages. Consumer-led food product development should be a standard procedure. The study aimed to develop a new variants of aerated tvarog spreads. METHODS The research was divided into the following steps: evaluation of consumer pref- erences (questionnaire); production of aerated tvarog cheeses (different flavor variants); physico-chemical evaluation of new products (composition, TPA test); evaluation of new products by consumers (questionnaire with a 5-point scale); sensory evaluation of new products by an expert panel (2 types of questionnaire). RESULTS Sweet tvarog spreads were characterized by a higher degree of aeration than cheeses with a savory flavor. The savory variants had a semi-liquid consistency after aeration. This could result from the addition of salt (6%) to flavor preparation. The products stabilized by gelatine showed a higher degree of aeration than the ones with starch. The savory cheeses showed lower hardness than sweet cheeses (P < 0.05). Both consum- ers and experts gave higher marks to the sweet variants of manufactured tvarog cheeses. CONCLUSIONS The addition of salt to savory flavor preparation probably affected the texture of these products, which was semi-liquid. Texture plays a very important role in the development of new products and affects consumers’ preferences for the product.

Raw skim milk was subjected to different heat treatments: thermization (65°C, 20 s), pasteurization (72°C, 15 s), and no heat treatment (milk was microfiltered using 1.4-µm membranes at 50°C for bacteria removal; 1.4 MF). The milk (thermized, pasteurized, and 1.4 MF) was cooled and stored at 2°C until processing (at least 24 h) with cold (∼6°C) microfiltration using a benchtop crossflow pilot unit (Pall Membralox XLAB 5, Pall Corp., Port Washington, NY) equipped with 0.1-µm nominal pore diameter ceramic Membralox membrane (ET1-070, α-alumina, Pall Corp.). The flux was monitored during the process, and β-casein transmission and removal were calculated. The study aimed to indicate the conditions that should be applied to maximize β-casein passage through the membrane during cold microfiltration (5.6 ± 0.4°C) of skim milk. The proper selection of heat treatment parameters (temperature, time) of the feed before the cold microfiltration process will increase β-casein removal. It is not clear whether the difference in β-casein transmission between 1.4 MF, thermized, and pasteurized milk results from the effect of heat treatment conditions on β-casein dissociation from the casein micelles or on passage of β-casein through the membrane. The values of the major parameters (permeation flux and tangential flow velocity, through the wall shear stress) responsible for a proper membrane separation process were considerably lower than the critical values. It seems that the viscosity of the retentate has a great effect on the performance of the microfiltration membranes for protein separation at refrigerated temperatures.

The physical properties of milk fat are affected by the structure and distribution of fatty acids (FAs) within the triacylglycerols (TAGs). The impact of variable seasonal composition of milk fat components was studied with respect to the influence on the physical and rheological properties of butter. Rather than analysing individual samples, a dynamic system was studied to capture the impact statistically. A significant seasonal variation in the rheological features (penetration) of butter was noted. A polynomial function approximated the relationship between butter penetration and measurement temperature, while butter from the summer season was more susceptible to changes in penetration in response to temperature changes than butter from the winter season. A significant impact on the rheological properties of butter had the ratios of the FA content: C14:0/C18:1, C16:0/C18:1 and total unsaturated fatty acids to total saturated fatty acids, and proportions of the TAG content: Cn36/Cn40, Cn46/Cn50 and Cn40/Cn46.

Pasteurized skim milk was subjected to (1) microfiltration (MF) at 50°C and (2) MF at 6°C after storage at 2°C. The products of these treatments were retentate (RMF50) and permeate (PMF50), and retentate (RMF6) and permeate (PMF6), respectively. Additionally, RMF50 was subjected to (3) cold MF after water dilution to produce retentate (RMF6R) and permeate (PMF6R). Calcium migration was monitored by analyzing ionic, soluble, and total calcium content in feed, retentates, and permeates. The influence of calcium partitioning and calcium addition to feed, retentates, and retentates diluted with water was determined. Without CaCl2 addition, only skim milk, RMF50, and RMF6 coagulated after rennet addition. Higher true protein and casein content of RMF50 and RMF6 resulted in shorter time of renneting. The retentates diluted with water showed no signs of coagulation within 40 min. The addition of PMF6R to RMF50 did not affect rennet coagulation time within the observed 40 min in comparison to RMF50 + water. In general, higher CaCl2 addition resulted in shorter rennet coagulation time. Special attention should be paid to calcium partitioning during membrane processing of cheesemilk. The level of calcium addition should be adopted to calcium content in such cheesemilk, which is affected by conditions of the filtration process (i.e., concentration factor and temperature).

The aim of this work was to evaluate the growth possibilities of Listeria monocytogens in the artificially contaminated fresh cheese during storage. Three variants of acid homogenized commercial fresh cheeses: mixed herbs, red pepper and garlic-pepper were studied. The lowest value of the specific growth rate of L. monocytogenes in the fresh cheeses was reported for red pepper variant. The highest value of this parameter was determined for the fresh cheese with pepper-garlic. The use of spices in the production of fresh unripened cheeses influence the viability and growth of bacteria L. monocytogenes during storage at the temperature range 3-15oC.

Summary Behaviour of Yersinia enterocolitica in mould-ripened Camembert-type cheese during storage at temperature range 3–15 °C was evaluated and mathematically described. The Baranyi and Gompertz models were adjusted to the results of the study to calculate the growth rate (GR) and lag time (LT) for Y. enterocolitica at each temperature. Goodness of fit was assessed by calculating the Akaike information criterion (AIC) and mean square error (MSE). Square root models were constructed which described the relations between GR, LT and applied storage temperature. The secondary models were mathematically validated based on the results generated by ComBase Predictor. Moreover, generated models were validated using external, independent data from ComBase database. Based on this, it was found that the square root models of Ratkowsky constructed on GR that were determined based on the Baranyi and Roberts model most accurately described the behaviour of Y. enterocolitica in Camembert-type cheese during storage under refrigerated conditions.

The growth of Listeria monocytogenes was determined in Ultra-High-Temperature (UHT) dairy products (2% milk, 12 and 30% cream) at temperature range of 3–15C. Microbiological data were fitted to primary models (the Baranyi model, the modified Gompertz and logistic functions). The goodness-of-fit of primary models was analyzed by calculating mean square error and Akaike's information criterion. Baranyi model yielded the most accurate adjustment and the growth rates generated by this model were used for further mathematical analyses. Analysis of variance was used to check if the fat content significantly (P

This study presents possible applications of predictive microbiology to model the safety of mold-ripened cheeses with respect to bacteria of the species Listeria monocytogenes during (1) the ripening of Camembert cheese, (2) cold storage of Camembert cheese at temperatures ranging from 3 to 15°C, and (3) cold storage of blue cheese at temperatures ranging from 3 to 15°C. The primary models used in this study, such as the Baranyi model and modified Gompertz function, were fitted to growth curves. The Baranyi model yielded the most accurate goodness of fit and the growth rates generated by this model were used for secondary modeling (Ratkowsky simple square root and polynomial models). The polynomial model more accurately predicted the influence of temperature on the growth rate, reaching the adjusted coefficients of multiple determination 0.97 and 0.92 for Camembert and blue cheese, respectively. The observed growth rates of L. monocytogenes in mold-ripened cheeses were compared with simulations run with the Pathogen Modeling Program (PMP 7.0, USDA, Wyndmoor, PA) and ComBase Predictor (Institute of Food Research, Norwich, UK). However, the latter predictions proved to be consistently overestimated and contained a significant error level. In addition, a validation process using independent data generated in dairy products from the ComBase database (www.combase.cc) was performed. In conclusion, it was found that L. monocytogenes grows much faster in Camembert than in blue cheese. Both the Baranyi and Gompertz models described this phenomenon accurately, although the Baranyi model contained a smaller error. Secondary modeling and further validation of the generated models highlighted the issue of usability and applicability of predictive models in the food processing industry by elaborating models targeted at a specific product or a group of similar products.

S t r e s z c z e n i e Obserwuje sie wzrost zachorowan wynikający z obecności drobnoustrojow chorobotworczych w produktach spozywczych. Proces szacowania ryzyka umozliwia ocene narazenia zdrowia czlowieka na mikroorganizmy obecne w zywności. Narzedziem do ilościowej oceny zachowania drobnoustrojow w zywności są modele prognostyczne. Celem pracy byla ocena przezywalności bakterii Bacillus cereus w serach typu feta i mozzarella podczas przechowywania w temperaturze 3 - 15 oC, przy uzyciu impedymetrycznego systemu Bactrac oraz opracowanie wynikow metodą mikrobiologii prognostycznej. Zastosowano aplikacje DMFit i porownano parametry wzrostu z danymi uzyskanymi w programie prognostycznym ComBase Predictor (CP). Prognozy w CP pochodzą z danych uzyskanych na pozywkach mikrobiologicznych (zmodyfikowanych pod wzgledem skladu). Stwierdzono, ze sery typu feta i mozzarella w przyjetych warunkach doświadczenia stanowily dobrą pozywke do rozwoju bakterii B. cereus. Uzyskane z doświadczen oraz wyliczen matematycznych modele wzrostu B. cereus podczas przechowywania serow typu feta i mozzarella roznily sie od prognoz uzyskanych w programie CP. Parametrem wzrostu określającym bezpieczenstwo mikrobiologiczne serow typu feta i mozzarella byl czas trwania lag fazy. Slowa kluczowe: mikrobiologia prognostyczna, Bacillus cereus, feta, mozzarella, bezpieczenstwo zywności