Alfredo Palop | Universidad Politecnica de Cartagena (original) (raw)

Papers by Alfredo Palop

Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious f... more Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious food-borne diseases in the world, listeriosis. The aim of this study is to eva-luate the combined effect of a heat pretreatment with the use of antimicrobials, nisin and carvacrol, on the growth of L. monocytogenes, and their potential uses as food preserva-tives. Carvacrol showed a dose-dependent inhibitory effect, while nisin did not, it decreas-ed the growth rate of L. monocytogenes up to 20 %, and it increased lag time for approx. 25 % at any of the concentrations tested (0.13–0.39 mM). When both antimicrobials were com-bined, a synergistic effect was observed. This effect was further increased when they were combined with a heat pretreatment for 15 min at 55 °C, where no growth was observed for at least 15 days, even at the lowest concentration tested. The effect was proved both in tryptic soy broth and in carrot juice. This study indicates the potential use of carvacrol and nisin ap...

Scientific Reports, 2020

Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years. T... more Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years. This type of products have minimal processing conditions that can enable the survival and replication of pathogenic microorganisms. Among them, Listeria monocytogenes is of special concern, due to its relatively high mortality rate and its ability to replicate under refrigeration conditions. Previous research works have shown that nanoemulsified essential oils in combination with thermal treatments are effective for inactivating L. monocytogenes. However, previous research works were limited to isothermal conditions, whereas actual processing conditions in industry are dynamic. Under dynamic conditions, microorganism can respond unexpectedly to the thermal stress (e.g. adaptation, acclimation or increased sensitivity). In this work, we assess the combination of nanoemulsified D-limonene with thermal treatments under isothermal and dynamic conditions. The nanoemulsion was prepared followin...

Frontiers in Microbiology

Microbial cells respond to sub-lethal stresses with several physiological changes to increase the... more Microbial cells respond to sub-lethal stresses with several physiological changes to increase their chance of survival. These changes are of high relevance when combined treatments (hurdle technology) are applied during food production, as the cells surviving the first hurdle may have greater resistance to subsequent treatments than untreated cells. In this study, we analyzed if Salmonella develops increased resistance to thermal treatments after the application of an acid shock. We compared the heat resistance of acid-shocked (pH 4.5 achieved with citric acid) Salmonella cells with that of cells maintained at pH 7 (control cells). Thermal treatments were performed between 57.5 and 65°C. We observed a differential response between the two strains studied. Acid-shocked cells of Salmonella Senftenberg exhibited reduced heat resistance, e.g., for a treatment at 60.0°C and pH 7.0 the time required to reduce the population by 3 log cycles was lowered from 10.75 to 1.98min with respect to...

Foods

In the food science field, the term “antimicrobial” basically refers to active substances of synt... more In the food science field, the term “antimicrobial” basically refers to active substances of synthetic or natural origin, that are directly or indirectly present in a specific food, packaging material or food contact surface that affect the viability or the growth of microorganisms in that matrix [...]

Foods

Biofilms represent a serious problem for food industries due to their persistence in processing s... more Biofilms represent a serious problem for food industries due to their persistence in processing surfaces, from which they can cause food spoilage or, even worse, lead to foodborne diseases. Microorganisms immersed in biofilms are more resistant to biocides. The search for natural effective alternatives for the prevention and the control of biofilms has increased lately. The aim of this research was to test the antibacterial and the anti-biofilm activities of cinnamon, onion, and garlic essential oils against Listeria monocytogenes. The methodology highlighted first the effect of these essential oils on L. monocytogenes using disc diffusion and minimum inhibitory concentration (MIC) methods and then on initial cell attachment and six hours preformed biofilms. The inhibition of biofilms was assessed by crystal violet assay. Sulfides were the most abundant compounds present in onion and garlic essential oils, while cinnamaldehyde was predominant in cinnamon essential oil. MIC values we...

Frontiers in microbiology, 2018

Decisions regarding microbial risk assessment usually have to be carried out with incomplete info... more Decisions regarding microbial risk assessment usually have to be carried out with incomplete information. This is due to the large number of possible scenarios and the lack of specific data for the problem considered. Consequently, risk assessment studies are based on the information obtained with a small number of bacterial cells which are considered the most heat resistant and/or more capable of multiplying during storage. The identification of the most resistant strains is usually based on D and z-values, normally estimated from isothermal experiments. This procedure omits the potential effect that the shape of the dynamic thermal profile applied in industry has on the microbial inactivation. One example of such effects is stress acclimation, which is related to a physiological response of the cells during sub-lethal treatments that increases their resistance. In this article, we use a recently published mathematical model to compare the development of thermal resistance for K12 ...

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...

Nanomaterials

Salmonella Senftenberg is a pathogen agent causative of foodborne disease and it is considered th... more Salmonella Senftenberg is a pathogen agent causative of foodborne disease and it is considered the most heat-resistant serovar within this genus. Food industries use heat treatment and chemical antimicrobials in order to eliminate this microorganism in food, but consumers prefer natural antimicrobials as essential oils and their components. This study evaluates the combined effect of thermal treatments and different concentrations of D-limonene nanoemulsion on the inactivation of Salmonella (S.) Senftenberg. The results showed an important effect of the nanoemulsified D-limonene on the heat resistance of S. Senftenberg. The δ 50 • C value was reduced by 85%, 96% and 98% when 0.1, 0.5 and 1 mM of nanoemulsified D-limonene was added to the heating medium. The effect was kept along all the heating temperatures researched and the shape of the survival curves did not change with the addition of the antimicrobial. The results obtained in this research could be very useful for food industries for optimizing or improving heat treatments applied to food.

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.

Food Technology and Biotechnology, 2011

Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious f... more Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious food-borne diseases in the world, listeriosis. The aim of this study is to evaluate the combined effect of a heat pretreatment with the use of antimicrobials, nisin and carvacrol, on the growth of L. monocytogenes, and their potential uses as food preservatives. Carvacrol showed a dose-dependent inhibitory effect, while nisin did not, it decreased the growth rate of L. monocytogenes up to 20 %, and it increased lag time for approx. 25 % at any of the concentrations tested (0.13-0.39 mM). When both antimicrobials were combined, a synergistic effect was observed. This effect was further increased when they were combined with a heat pretreatment for 15 min at 55°C, where no growth was observed for at least 15 days, even at the lowest concentration tested. The effect was proved both in tryptic soy broth and in carrot juice. This study indicates the potential use of carvacrol and nisin applied simultaneously for preservation of minimally processed foods.

Eur Food Res Technol, 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.

International Journal of Food Microbiology, Feb 18, 1999

The influence of pH of heating menstruum (McIlvaine buffer) on the heat resistance of Bacillus co... more The influence of pH of heating menstruum (McIlvaine buffer) on the heat resistance of Bacillus coagulans spores has been investigated and compared with the heat resistance in homogenized tomato and asparagus at pH 7 and 4 at a wide range of temperatures. Spores were less heat resistant in all menstrua at acid pH. The magnitude of this effect was greatest at the lowest heating temperatures tested. z values in buffer increased from 8.98C at pH 7 to 10.58C at pH 4. pH of menstrua was the main influencing factor, but media composition also influenced heat resistance: at pH 7 heat resistance was similar in all menstrua (D 5 1.6 min) but at pH 4 the heat resistance in homogenized foods (D 5 0.26 min in tomato and 1118C 1118C D 5 0.28 min in asparagus) was lower than in buffer (D 5 0.49 min). The reduced influence of the acidification of 1118C 1118C media on the heat resistance of B. coagulans at higher temperatures should be taken into account when a rise in the temperature of treatment for canned vegetables is considered to shorten duration of heat processes.

ABSTRACT Summary Minimal processing implementation greatly depends on a detailed knowledge of the... more ABSTRACT Summary Minimal processing implementation greatly depends on a detailed knowledge of the effects of preservation factors and their combinations on the spoilage and foodborne pa- thogenic microorganisms. The effectiveness of mild preservation conditions will become increasingly dependent on a more stochastic approach linking microbial physiological fac- tors with product preservation factors. In this study, the validity of frequency distributions to efficiently describe the inactivation and growth of Bacillus cereus in the presence of natu- ral antimicrobials (essential oils) has been studied. For this purpose, vegetative cells were exposed to 0.6 mM of thymol or cymene, obtaining survival curves that were best de- scribed by the distribution of Weibull, since a tailing effect was observed. B. cereus was also exposed in a growth medium to a low concentration (0.1 mM) of both antimicrobials, separately or combined, and the lag times obtained were fitted to a normal distribution, which allowed a description of dispersion of the start of growth. This allowed a more effi- cient evaluation of the experimental data to establish safe processing conditions according to accurate parameters and their implementation in risk assessment.

Contemporary Food Engineering, 2012

Food Research International, 2015

ABSTRACT Abstract Cronobacter sakazakii is an opportunistic pathogen in neonates which can cause ... more ABSTRACT Abstract Cronobacter sakazakii is an opportunistic pathogen in neonates which can cause meningitis, septicaemia and enterocolitis related to the consumption of contaminated Powdered Infant Formula (PIF). C. sakazakii has an unusual ability to survive under dry conditions and it could be among the most thermotolerant members of the Enterobacteriaceae. Little is known about how Cronobacter species respond to heat stress and the mechanisms involved in the process. In the current study we determined the heat resistance of a particularly stress tolerant C. sakazakii strain, C. sakazakii DPC 6529, and monitored the behavior of a lux-tagged derivative under different reconstitution and handling scenarios in a commercial brand of PIF. Some of the molecular mechanisms involved in the heat stress response were investigated using a transposon mutagenesis approach. Survival curves of C. sakazakii DPC 6529 in Luria-Bertani (LB) broth and PIF at various temperatures (58, 60, 62 and 64 °C) displayed an upward concavity and were fitted to the non-linear Weibull model. While at the highest treatment temperatures heat resistance was lower in PIF than in LB broth, at lower temperatures no significant differences in heat resistance were observed. Experiments in real time with artificially inoculated PIF reconstituted at different water temperatures (50, 55, 60, 65, 70 °C) and cooled at different rates confirmed that C. sakazakii can survive for long time periods in powdered formula, and is capable of proliferating after reconstitution. The use of water at temperatures between 50 and 65 °C for reconstitution did not provide a significant inactivation of C. sakazakii cells. Reconstitution at 70 °C reduced the bacterium to levels below the detection limit, although survivors were able to proliferate and reached dangerous levels when the reconstituted product was stored for a long time at room temperature. The cooling rate had an important impact on survival and subsequent growth of C. sakazakii, which makes it advisable to avoid rapid cooling of baby formula. Transposon mutagenesis allowed the identification of some of the molecular mechanisms involved in the response of C. sakazakii DPC6529 to heat stress. Genes identified included the Ribosome Maturation Protein RimP and Outer Membrane Porin L (OmpL). Results suggest that de novo protein synthesis, and the uptake of cysteine for the formation of disulfide bonds for protein stabilization, are key processes.

International Journal of Food Microbiology, 2006

International Journal of Food Microbiology

The heat resistance of the bacterial spores of Moorella thermoacetica, Clostridium sporogenes, Ge... more The heat resistance of the bacterial spores of Moorella thermoacetica, Clostridium sporogenes, Geobacillus stearothermophilus and Bacillus coagulans was determined over a wide range of temperatures using the capillary method and thermoresistometer Mastia. The results showed that the two experimental methods gave similar heat resistance values excepted for Geobacillus stearothermophilus. The effect of temperature on thermal resistance was evaluated using the Arrhenius and Bigelow models. The fit of the heat sensitivity parameters of the Arrhenius and Bigelow models on the heat resistance parameter values obtained over a wide temperature range was equally good. Despite the apparent mathematical incompatibility of the two equations, it is recognized that they yield the same goodness of fit. This paper finds a mathematical reason for this convergence and explains why inside a temperature range of at least 100 °C, no significant difference in the quality of fit between these two models can be found.

Food Engineering Reviews, 2009

In general, food engineers are trained to solve engineering problems in the food industry. More s... more In general, food engineers are trained to solve engineering problems in the food industry. More specifically, the food engineer must specify the functional requirements, design, and testing of food products, and finally, the evaluation of products to check for overall efficiency, cost, reliability, and most importantly, safety. Food safety must be considered foremost as the overall engineering problem encountered in the food supply chain, and it must be solved from a food safety engineering perspective. This article will show that the food safety engineering perspective is needed in order to produce high quality food products (minimally processed) that are both safe and secure. This multi-disciplinary approach will involve certain engineering components: (i) predictive microbiology as a tool to evaluate and improve food safety in traditional and new processing technologies, (ii) advanced food contaminants detection methods, (iii) advanced processing technologies, (iv) advanced systems for re-contamination control, (v) advanced systems for active and intelligent packaging.

Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious f... more Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious food-borne diseases in the world, listeriosis. The aim of this study is to eva-luate the combined effect of a heat pretreatment with the use of antimicrobials, nisin and carvacrol, on the growth of L. monocytogenes, and their potential uses as food preserva-tives. Carvacrol showed a dose-dependent inhibitory effect, while nisin did not, it decreas-ed the growth rate of L. monocytogenes up to 20 %, and it increased lag time for approx. 25 % at any of the concentrations tested (0.13–0.39 mM). When both antimicrobials were com-bined, a synergistic effect was observed. This effect was further increased when they were combined with a heat pretreatment for 15 min at 55 °C, where no growth was observed for at least 15 days, even at the lowest concentration tested. The effect was proved both in tryptic soy broth and in carrot juice. This study indicates the potential use of carvacrol and nisin ap...

Scientific Reports, 2020

Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years. T... more Consumers’ demands for ready-to-eat, fresh-like products are on the rise during the last years. This type of products have minimal processing conditions that can enable the survival and replication of pathogenic microorganisms. Among them, Listeria monocytogenes is of special concern, due to its relatively high mortality rate and its ability to replicate under refrigeration conditions. Previous research works have shown that nanoemulsified essential oils in combination with thermal treatments are effective for inactivating L. monocytogenes. However, previous research works were limited to isothermal conditions, whereas actual processing conditions in industry are dynamic. Under dynamic conditions, microorganism can respond unexpectedly to the thermal stress (e.g. adaptation, acclimation or increased sensitivity). In this work, we assess the combination of nanoemulsified D-limonene with thermal treatments under isothermal and dynamic conditions. The nanoemulsion was prepared followin...

Frontiers in Microbiology

Microbial cells respond to sub-lethal stresses with several physiological changes to increase the... more Microbial cells respond to sub-lethal stresses with several physiological changes to increase their chance of survival. These changes are of high relevance when combined treatments (hurdle technology) are applied during food production, as the cells surviving the first hurdle may have greater resistance to subsequent treatments than untreated cells. In this study, we analyzed if Salmonella develops increased resistance to thermal treatments after the application of an acid shock. We compared the heat resistance of acid-shocked (pH 4.5 achieved with citric acid) Salmonella cells with that of cells maintained at pH 7 (control cells). Thermal treatments were performed between 57.5 and 65°C. We observed a differential response between the two strains studied. Acid-shocked cells of Salmonella Senftenberg exhibited reduced heat resistance, e.g., for a treatment at 60.0°C and pH 7.0 the time required to reduce the population by 3 log cycles was lowered from 10.75 to 1.98min with respect to...

Foods

In the food science field, the term “antimicrobial” basically refers to active substances of synt... more In the food science field, the term “antimicrobial” basically refers to active substances of synthetic or natural origin, that are directly or indirectly present in a specific food, packaging material or food contact surface that affect the viability or the growth of microorganisms in that matrix [...]

Foods

Biofilms represent a serious problem for food industries due to their persistence in processing s... more Biofilms represent a serious problem for food industries due to their persistence in processing surfaces, from which they can cause food spoilage or, even worse, lead to foodborne diseases. Microorganisms immersed in biofilms are more resistant to biocides. The search for natural effective alternatives for the prevention and the control of biofilms has increased lately. The aim of this research was to test the antibacterial and the anti-biofilm activities of cinnamon, onion, and garlic essential oils against Listeria monocytogenes. The methodology highlighted first the effect of these essential oils on L. monocytogenes using disc diffusion and minimum inhibitory concentration (MIC) methods and then on initial cell attachment and six hours preformed biofilms. The inhibition of biofilms was assessed by crystal violet assay. Sulfides were the most abundant compounds present in onion and garlic essential oils, while cinnamaldehyde was predominant in cinnamon essential oil. MIC values we...

Frontiers in microbiology, 2018

Decisions regarding microbial risk assessment usually have to be carried out with incomplete info... more Decisions regarding microbial risk assessment usually have to be carried out with incomplete information. This is due to the large number of possible scenarios and the lack of specific data for the problem considered. Consequently, risk assessment studies are based on the information obtained with a small number of bacterial cells which are considered the most heat resistant and/or more capable of multiplying during storage. The identification of the most resistant strains is usually based on D and z-values, normally estimated from isothermal experiments. This procedure omits the potential effect that the shape of the dynamic thermal profile applied in industry has on the microbial inactivation. One example of such effects is stress acclimation, which is related to a physiological response of the cells during sub-lethal treatments that increases their resistance. In this article, we use a recently published mathematical model to compare the development of thermal resistance for K12 ...

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...

Nanomaterials

Salmonella Senftenberg is a pathogen agent causative of foodborne disease and it is considered th... more Salmonella Senftenberg is a pathogen agent causative of foodborne disease and it is considered the most heat-resistant serovar within this genus. Food industries use heat treatment and chemical antimicrobials in order to eliminate this microorganism in food, but consumers prefer natural antimicrobials as essential oils and their components. This study evaluates the combined effect of thermal treatments and different concentrations of D-limonene nanoemulsion on the inactivation of Salmonella (S.) Senftenberg. The results showed an important effect of the nanoemulsified D-limonene on the heat resistance of S. Senftenberg. The δ 50 • C value was reduced by 85%, 96% and 98% when 0.1, 0.5 and 1 mM of nanoemulsified D-limonene was added to the heating medium. The effect was kept along all the heating temperatures researched and the shape of the survival curves did not change with the addition of the antimicrobial. The results obtained in this research could be very useful for food industries for optimizing or improving heat treatments applied to food.

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.

Food Technology and Biotechnology, 2011

Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious f... more Listeria monocytogenes is a Gram-positive microorganism responsible for one of the most serious food-borne diseases in the world, listeriosis. The aim of this study is to evaluate the combined effect of a heat pretreatment with the use of antimicrobials, nisin and carvacrol, on the growth of L. monocytogenes, and their potential uses as food preservatives. Carvacrol showed a dose-dependent inhibitory effect, while nisin did not, it decreased the growth rate of L. monocytogenes up to 20 %, and it increased lag time for approx. 25 % at any of the concentrations tested (0.13-0.39 mM). When both antimicrobials were combined, a synergistic effect was observed. This effect was further increased when they were combined with a heat pretreatment for 15 min at 55°C, where no growth was observed for at least 15 days, even at the lowest concentration tested. The effect was proved both in tryptic soy broth and in carrot juice. This study indicates the potential use of carvacrol and nisin applied simultaneously for preservation of minimally processed foods.

Eur Food Res Technol, 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.

International Journal of Food Microbiology, Feb 18, 1999

The influence of pH of heating menstruum (McIlvaine buffer) on the heat resistance of Bacillus co... more The influence of pH of heating menstruum (McIlvaine buffer) on the heat resistance of Bacillus coagulans spores has been investigated and compared with the heat resistance in homogenized tomato and asparagus at pH 7 and 4 at a wide range of temperatures. Spores were less heat resistant in all menstrua at acid pH. The magnitude of this effect was greatest at the lowest heating temperatures tested. z values in buffer increased from 8.98C at pH 7 to 10.58C at pH 4. pH of menstrua was the main influencing factor, but media composition also influenced heat resistance: at pH 7 heat resistance was similar in all menstrua (D 5 1.6 min) but at pH 4 the heat resistance in homogenized foods (D 5 0.26 min in tomato and 1118C 1118C D 5 0.28 min in asparagus) was lower than in buffer (D 5 0.49 min). The reduced influence of the acidification of 1118C 1118C media on the heat resistance of B. coagulans at higher temperatures should be taken into account when a rise in the temperature of treatment for canned vegetables is considered to shorten duration of heat processes.

ABSTRACT Summary Minimal processing implementation greatly depends on a detailed knowledge of the... more ABSTRACT Summary Minimal processing implementation greatly depends on a detailed knowledge of the effects of preservation factors and their combinations on the spoilage and foodborne pa- thogenic microorganisms. The effectiveness of mild preservation conditions will become increasingly dependent on a more stochastic approach linking microbial physiological fac- tors with product preservation factors. In this study, the validity of frequency distributions to efficiently describe the inactivation and growth of Bacillus cereus in the presence of natu- ral antimicrobials (essential oils) has been studied. For this purpose, vegetative cells were exposed to 0.6 mM of thymol or cymene, obtaining survival curves that were best de- scribed by the distribution of Weibull, since a tailing effect was observed. B. cereus was also exposed in a growth medium to a low concentration (0.1 mM) of both antimicrobials, separately or combined, and the lag times obtained were fitted to a normal distribution, which allowed a description of dispersion of the start of growth. This allowed a more effi- cient evaluation of the experimental data to establish safe processing conditions according to accurate parameters and their implementation in risk assessment.

Contemporary Food Engineering, 2012

Food Research International, 2015

ABSTRACT Abstract Cronobacter sakazakii is an opportunistic pathogen in neonates which can cause ... more ABSTRACT Abstract Cronobacter sakazakii is an opportunistic pathogen in neonates which can cause meningitis, septicaemia and enterocolitis related to the consumption of contaminated Powdered Infant Formula (PIF). C. sakazakii has an unusual ability to survive under dry conditions and it could be among the most thermotolerant members of the Enterobacteriaceae. Little is known about how Cronobacter species respond to heat stress and the mechanisms involved in the process. In the current study we determined the heat resistance of a particularly stress tolerant C. sakazakii strain, C. sakazakii DPC 6529, and monitored the behavior of a lux-tagged derivative under different reconstitution and handling scenarios in a commercial brand of PIF. Some of the molecular mechanisms involved in the heat stress response were investigated using a transposon mutagenesis approach. Survival curves of C. sakazakii DPC 6529 in Luria-Bertani (LB) broth and PIF at various temperatures (58, 60, 62 and 64 °C) displayed an upward concavity and were fitted to the non-linear Weibull model. While at the highest treatment temperatures heat resistance was lower in PIF than in LB broth, at lower temperatures no significant differences in heat resistance were observed. Experiments in real time with artificially inoculated PIF reconstituted at different water temperatures (50, 55, 60, 65, 70 °C) and cooled at different rates confirmed that C. sakazakii can survive for long time periods in powdered formula, and is capable of proliferating after reconstitution. The use of water at temperatures between 50 and 65 °C for reconstitution did not provide a significant inactivation of C. sakazakii cells. Reconstitution at 70 °C reduced the bacterium to levels below the detection limit, although survivors were able to proliferate and reached dangerous levels when the reconstituted product was stored for a long time at room temperature. The cooling rate had an important impact on survival and subsequent growth of C. sakazakii, which makes it advisable to avoid rapid cooling of baby formula. Transposon mutagenesis allowed the identification of some of the molecular mechanisms involved in the response of C. sakazakii DPC6529 to heat stress. Genes identified included the Ribosome Maturation Protein RimP and Outer Membrane Porin L (OmpL). Results suggest that de novo protein synthesis, and the uptake of cysteine for the formation of disulfide bonds for protein stabilization, are key processes.

International Journal of Food Microbiology, 2006

International Journal of Food Microbiology

The heat resistance of the bacterial spores of Moorella thermoacetica, Clostridium sporogenes, Ge... more The heat resistance of the bacterial spores of Moorella thermoacetica, Clostridium sporogenes, Geobacillus stearothermophilus and Bacillus coagulans was determined over a wide range of temperatures using the capillary method and thermoresistometer Mastia. The results showed that the two experimental methods gave similar heat resistance values excepted for Geobacillus stearothermophilus. The effect of temperature on thermal resistance was evaluated using the Arrhenius and Bigelow models. The fit of the heat sensitivity parameters of the Arrhenius and Bigelow models on the heat resistance parameter values obtained over a wide temperature range was equally good. Despite the apparent mathematical incompatibility of the two equations, it is recognized that they yield the same goodness of fit. This paper finds a mathematical reason for this convergence and explains why inside a temperature range of at least 100 °C, no significant difference in the quality of fit between these two models can be found.

Food Engineering Reviews, 2009

In general, food engineers are trained to solve engineering problems in the food industry. More s... more In general, food engineers are trained to solve engineering problems in the food industry. More specifically, the food engineer must specify the functional requirements, design, and testing of food products, and finally, the evaluation of products to check for overall efficiency, cost, reliability, and most importantly, safety. Food safety must be considered foremost as the overall engineering problem encountered in the food supply chain, and it must be solved from a food safety engineering perspective. This article will show that the food safety engineering perspective is needed in order to produce high quality food products (minimally processed) that are both safe and secure. This multi-disciplinary approach will involve certain engineering components: (i) predictive microbiology as a tool to evaluate and improve food safety in traditional and new processing technologies, (ii) advanced food contaminants detection methods, (iii) advanced processing technologies, (iv) advanced systems for re-contamination control, (v) advanced systems for active and intelligent packaging.