Arturo Esnoz - Academia.edu (original) (raw)

Papers by Arturo Esnoz

Foods, 2021

Alicyclobacillus acidoterrestris is a spoilage microorganism responsible for relevant product and... more Alicyclobacillus acidoterrestris is a spoilage microorganism responsible for relevant product and economic losses in the beverage and juice industry. Spores of this microorganism can survive industrial heat treatments and cause spoilage during posterior storage. Therefore, an effective design of processing treatments requires an accurate understanding of the heat resistance of this microorganism. Considering that industrial treatments are dynamic; this understanding must include how the heat resistance of the microorganism is affected by the heating rate during the heating and cooling phases. The main objective of this study was to establish the effect of heating rates and complex thermal treatments on the inactivation kinetics of A. acidoterrestris. Isothermal experiments between 90 and 105 °C were carried out in a Mastia thermoresistometer, as well as four different dynamic treatments. Although most of the inactivation takes place during the holding phase, our results indicate the...

Food Research International, 2020

Microwave processing can be a valid alternative to conventional heating for different types of pr... more Microwave processing can be a valid alternative to conventional heating for different types of products. It enables a more efficient heat transfer in the food matrix, resulting in higher quality products. However, for many food products a uniform temperature distribution is not possible because of heterogeneities in their physical properties and non-uniformtiy in the electric field pattern. Hence, the effectiveness of microwave inactivation treatments is influenced by both intrinsic (differences between cells) and extrinsic variability (non-uniform temperature). Interpreting the results of the process and considering its impact on microbial inactivation is essential to ensure effective and efficient processing. In this work, we quantified the variability in microbial inactivation attained in a microwave pasteurization treatment with a tunnel configuration at pilot-plant scale. The configuration of the equipment makes it impossible to measure the product temperature during treatment. For that reason, variability in microbial counts was measured using Biological Inactivation Indicators (BIIs) based on spherical particles of alginate inoculated with spores of Bacillus spp. The stability of the BIIs and the uncertainty associated to them was assessed using preliminary experiments in a thermoresistometer. Then, they were introduced in the food product to analyse the microbial inactivation in different points of the products during the microwave treatment. Experiments were made in a vegetable soup and a fish-based animal by-product (F-BP). The results show that the variation in the microbial counts was higher than expected based on the biological variability estimated in the thermoresistometer and the uncertainty of the BIIs. This is due to heterogeneities in the temperature field (measured using a thermographic camera), which were higher in the F-BP than in the vegetable soup. Therefore, for the process studied, extrinsic variability was more relevant than intrinsic variability. The methodology presented in this work can be a valid method to evaluate pasteurization treatments of foods processed by heating, providing valuable information of the microbial inactivation achieved. It can contribute to design microwave processes for different types of products and for product optimization.

Food Research International, 2019

Kinetic models are nowadays a basic tool to ensure food safety. Most models used in predictive mi... more Kinetic models are nowadays a basic tool to ensure food safety. Most models used in predictive microbiology have model parameters, whose precision is crucial to provide meaningful predictions. Kinetic parameters are usually estimated based on experimental data, where the experimental design can have a great impact on the precision of the estimates. In this sense, Optimal Experiment Design (OED) applies tools from optimization and information theory to identify the most informative experiment under a set of constrains (e.g. mathematical model, number of samples,etc). In this work, we develop a methodology for the design of optimal isothermal inactivation experiments. We consider the two dimensions of the design space (time and temperature), as well as a temperature-dependent maximum duration of the experiment. Functions for its application have been included in the bioOED R package. We identify design patterns that remain optimum regardless of the number of sampling points for three inactivation models (Bigelow, Mafart and Peleg) and three model microorganisms (Escherichia coli, Salmonella Senftemberg and Bacillus coagulans). Samples at extreme temperatures and close to the maximum duration of the experiment are the most informative. Moreover, the Mafart and Peleg models require some samples at intermediate time points due to the non-linearity of the survivor curve. The impact of the reference temperature on the precision of the parameter estimates is also analysed. Based on numerical simulations we recommend fixing it to the mean of the maximum and minimum temperatures used for the experiments. The article ends with a discussion presenting guidelines for the design of isothermal inactivation experiments. They combine these optimum results based on information theory with several practical limitations related to isothermal inactivation experiments. The application of these guidelines would reduce the experimental burden required to characterize thermal inactivation.

PLOS ONE, 2019

The mathematical models used in predictive microbiology contain parameters that must be estimated... more The mathematical models used in predictive microbiology contain parameters that must be estimated based on experimental data. Due to experimental uncertainty and variability, they cannot be known exactly and must be reported with a measure of uncertainty (usually a standard deviation). In order to increase precision (i.e. reduce the standard deviation), it is usual to add extra sampling points. However, recent studies have shown that precision can also be increased without adding extra sampling points by using Optimal Experiment Design, which applies optimization and information theory to identify the most informative experiment under a set of constraints. Nevertheless, to date, there has been scarce contributions to know a priori whether an experimental design is likely to provide the desired precision in the parameter estimates. In this article, two complementary methodologies to predict the parameter precision for a given experimental design are proposed. Both approaches are based on in silico simulations, so they can be performed before any experimental work. The first one applies Monte Carlo simulations to estimate the standard deviation of the model parameters, whereas the second one applies the properties of the Fisher Information Matrix to estimate the volume of the confidence ellipsoids. The application of these methods to a case study of dynamic microbial inactivation, showing how they can be used to compare experimental designs and assess their precision, is illustrated. The results show that, as expected, the optimal experimental design is more accurate than the uniform design with the same number of data points. Furthermore, it is demonstrated that, for some heating profiles, the uniform design does not ensure that a higher number of sampling points increases precision. Therefore, optimal experimental designs are highly recommended in predictive microbiology.

Food Microbiology, 2018

Effect of storage conditions in the response of Listeria monocytogenes in a fresh purple vegetabl... more Effect of storage conditions in the response of Listeria monocytogenes in a fresh purple vegetable Smoothie compared with an acidified TSB medium.

International journal of food microbiology, Jan 27, 2017

This contribution presents a mathematical model to describe non-isothermal microbial inactivation... more This contribution presents a mathematical model to describe non-isothermal microbial inactivation processes taking into account the acclimation of the microbial cell to thermal stress. The model extends the log-linear inactivation model including a variable and model parameters quantifying the induced thermal resistance. The model has been tested on cells of Escherichia coli against two families of non-isothermal profiles with different constant heating rates. One of the families was composed of monophasic profiles, consisting of a non-isothermal heating stage from 35 to 70°C; the other family was composed of biphasic profiles, consisting of a non-isothermal heating stage followed by a holding period at constant temperature of 57.5°C. Lower heating rates resulted in a higher thermal resistance of the bacterial population. This was reflected in a higher D-value. The parameter estimation was performed in two steps. Firstly, the D and z-values were estimated from the isothermal experim...

Journal of Food Engineering, 2003

Disposal of agricultural and agro-food industry by-products has become an increasing environmenta... more Disposal of agricultural and agro-food industry by-products has become an increasing environmental problem. Drying is one of the possible conditioning processes that can be applied to these by-products before using them as cattle feed or soil conditioner. In this paper, a dynamic model to simulate the dehydration process of wastes of vegetable from a wholesale market in a rotary dryer is proposed. The dryer was divided into 10 sections and mass and energy balances were established in each of them. The results have been validated in a semi-industrial dryer. The model predicts air and product moisture and temperature depending on working conditions of the rotary dryer. Inlet air temperature has been shown to be the variable that has the greatest effect, on both outlet moisture content of the product and on outlet air temperature.

Journal of Applied Microbiology, 2009

Aims: To design and build a thermoresistometer, named Mastia, which could perform isothermal and ... more Aims: To design and build a thermoresistometer, named Mastia, which could perform isothermal and nonisothermal experiments. Methods and Results: In order to evaluate the thermoresistometer, the heat resistance of Escherichia coli vegetative cells and Alicyclobacillus acidoterrestris spores was explored. Isothermal heat resistance of E. coli was characterized by D 60°C = 0AE38 min and z = 4AE7°C in pH 7 buffer. When the vegetative cells were exposed to nonisothermal conditions, their heat resistance was largely increased at slow heating and fast cooling rates. Isothermal heat resistance of A. acidoterrestris was characterized by D 95°C = 7AE4 min and z = 9AE5°C in orange juice. Under nonisothermal conditions, inactivation was reasonably well predicted from isothermal data. Conclusions: The thermoresistometer Mastia is a very suitable instrument to get heat resistance data of microorganisms under isothermal and nonisothermal treatments. Significance and Impact of the Study: The thermoresistometer Mastia can be a helpful tool for food processors in order to estimate the level of safety of the treatments they apply.

European Food Research and Technology, 2003

Different inactivation kinetics data have been used to predict the number of survivors exposed to... more Different inactivation kinetics data have been used to predict the number of survivors exposed to a heat treatment and, in consequence, to design thermal processes for the food industry. In this work, spores of an acidophilic strain of Bacillus subtilis were heated under isothermal and non-isothermal conditions. Experimental results obtained after isothermal treatments were analysed using the classical two-step linear regression procedure and a one-step non-linear regression method. Data obtained after non-isothermal treatments were analysed using a one-step, non-linear procedure. Kinetic parameters obtained from isothermal heating were close, either using the two-step linear regression (D 100 =6.5 min) or the one-step non-linear regression (D 100 =6.3 min), although the second method gave smaller 95% confidence intervals. The z values derived from non-isothermal heating were higher than those obtained in isothermal conditions (z=9.3 C for non-isothermal heating at 1 C/min versus z=7.7 C for isothermal heating one step non-linear regression). Results were validated with experimental data obtained after different heat treatments, consisting of a phase of temperature increase at a fixed rate, followed by a holding phase. Non-isothermal methods predicted accurately the number of survivors after the heating ramp, while isothermal methods were more accurate for the holding phase of the treatment. When a temperature profile of a typical heat treatment process applied in the food industry was simulated, all predictions were on the safe side.

Biosystems Engineering, 2004

A mathematical model based on dynamic heat and mass balances was developed to simulate grain and ... more A mathematical model based on dynamic heat and mass balances was developed to simulate grain and air temperature in a bin storage during rough rice forced aeration periods. The mathematical model includes several experimentally obtained expressions to determine thermo-physical grain properties. Model validation was carried out by comparing predicted with experimentally measured grain temperatures in different points of a pilot silo, ventilated with cool air at constant air temperature and humidity. Predicted and measured data were in close agreement. The model can be used to predict the development of grain temperature and the time needed to cool stored grain under different ventilation conditions.

Biosystems Engineering, 2004

Temperature and moisture content are the two main factors that affect grain storage without aerat... more Temperature and moisture content are the two main factors that affect grain storage without aeration. A twodimensional, finite difference model was developed to predict temperature and moisture content of rough rice stored in a cylindrical bin subjected to variations in ambient air temperature variation. Mass transfer is considered to affect heat transfer model and also mass and heat transfer are linked by the moisture content dependent thermo-physical properties of rough rice. Model validation was made by comparing predicted with experimental measured temperature data at different points of a pilot silo. The proposed model can be used to optimise the design and operation of rough rice storage systems.

L'invention concerne un thermoresistometre qui comprend un serpentin de refrigeration (6) et ... more L'invention concerne un thermoresistometre qui comprend un serpentin de refrigeration (6) et regule la temperature a l'aide d'une unite d'identification personnelle au moyen d'un automate (11) programmable et effectue une surveillance a l'aide d'un systeme Scada. Il est ainsi possible de realiser non seulement des traitements thermiques a temperature constante mais encore de simuler des rampes de chauffage et de refroidissement complexes ainsi que des traitements thermiques complets, aussi bien discontinus que continus, et d'enregistrer l'evolution de la temperature atteinte.

PLOS ONE, 2019

Food Research International

The estimation of the concentration of microorganisms in a sample is crucial for food microbiolog... more The estimation of the concentration of microorganisms in a sample is crucial for food microbiology. For instance, it is essential for prevalence studies, challenge tests (growth and/or inactivation studies) or microbial risk assessment. The application of serial dilutions followed by viable counts in Petri dishes is probably the most extended experimental methodology for this purpose. However, this enumeration technique is also a source of uncertainty. In this article, the uncertainty of the serial dilution and viable count methodology related to the sampling error is analyzed, as well as the approximation of the microbial concentration by the number of colonies in a Petri dish. We analyze from a theoretical point of view (statistical analysis) the application of the binomial and Poisson models, demonstrating that the Poisson distribution increases the variance when used to model individual serial dilutions. On the other hand, the binomial model produces unbiased results. Therefore, the Poisson distribution is only applicable when it is a good approximation of the binomial distribution, so the use of the latter is recommended. The relevance of this uncertainty is demonstrated by Monte Carlo simulations of a generic microbial inactivation experiment, where the only source of uncertainty/variability considered is the one generated by serial plating and viable cell enumeration. Due to both the uncertainty of the methodology and the omission of zero-count plates because of the log-transformation, the simulated survival curve can have a tail. Therefore, this phenomenon, which is usually attributed to biological variability, can be to some extent an artefact of the experimental design and/or methodology.

Frontiers in Microbiology, 2016

Heat resistance of microorganisms can be affected by different influencing factors. Although, the... more Heat resistance of microorganisms can be affected by different influencing factors. Although, the effect of heating rates has been scarcely explored by the scientific community, recent researches have unraveled its important effect on the thermal resistance of different species of vegetative bacteria. Typically heating rates described in the literature ranged from 1 to 20 • C/min but the impact of much higher heating rates is unclear. The aim of this research was to explore the effect of different heating rates, such as those currently achieved in the heat exchangers used in the food industry, on the heat resistance of Escherichia coli. A pilot plant tubular heat exchanger and a thermoresistometer Mastia were used for this purpose. Results showed that fast heating rates had a deep impact on the thermal resistance of E. coli. Heating rates between 20 and 50 • C/min were achieved in the heat exchanger, which were much slower than those around 20 • C/s achieved in the thermoresistometer. In all cases, these high heating rates led to higher inactivation than expected: in the heat exchanger, for all the experiments performed, when the observed inactivation had reached about seven log cycles, the predictions estimated about 1 log cycle of inactivation; in the thermoresistometer these differences between observed and predicted values were even more than 10 times higher, from 4.07 log cycles observed to 0.34 predicted at a flow rate of 70 mL/min and a maximum heating rate of 14.7 • C/s. A quantification of the impact of the heating rates on the level of inactivation achieved was established. These results point out the important effect that the heating rate has on the thermal resistance of E. coli, with high heating rates resulting in an additional sensitization to heat and therefore an effective food safety strategy in terms of food processing.

Journal of Food Engineering, 2003

Biosystems Engineering, 2004

Food Control, 1999

This paper presents a new control strategy for the wine fermentation process based on fermentatio... more This paper presents a new control strategy for the wine fermentation process based on fermentation rate control. A kinetic model of white wine fermentation has been constructed with the objective of testing the control procedure. The model only depends on very few quality parameters of the original must and can be executed in real-time, thus it can be used in real-time model-based control. A control methodology based on fermentation rate has therefore been developed, and a fuzzy multivariable controller was implemented. Further studies using dierent values for fermentation rate are discussed. Ó

Foods, 2021

Food Research International, 2020

Food Research International, 2019

PLOS ONE, 2019

Food Microbiology, 2018

International journal of food microbiology, Jan 27, 2017

Journal of Food Engineering, 2003

Journal of Applied Microbiology, 2009

European Food Research and Technology, 2003

Biosystems Engineering, 2004

PLOS ONE, 2019

Food Research International

Frontiers in Microbiology, 2016

Journal of Food Engineering, 2003

Biosystems Engineering, 2004

Food Control, 1999