Tom Rimaux - Academia.edu (original) (raw)

Papers by Tom Rimaux

Research paper thumbnail of Adaptation of Lactobacillus fermentum IMDO 130101 to the sourdough ecosystem through mannitol production and arginine conversion

Research paper thumbnail of The effect of cooling on crystallization and physico-chemical properties of puff pastry shortening made of palm oil and anhydrous milk fat blends

Journal of Food Engineering, 2021

Assessing the creditworthiness of technology startups could be a game-changer for Jabil's custome... more Assessing the creditworthiness of technology startups could be a game-changer for Jabil's customer expansion strategy. Candy Mitchell, Information Technology Director at Jabil Inc., sank into her desk chair and looked out the window pensively. She had just finished reading a report from her team of data scientists about a predictive model they had created. She saw huge potential in this model as a potential solution to power Jabil's customer growth strategy. Part of the strategy was to engage with technology startup companies to be their partner of choice from ideation to supply chain management. Working with technology startups would be new for Jabil and could create huge returns (when one of those technology startups took off, so would Jabil). Typical customers for Jabil (a manufacturing solutions provider that delivers comprehensive design, manufacturing, supply chain and product management services) ranged from FORTUNE® 500s to governments. Mitchell knew how risky startup customers could be, and Jabil only wanted to work with financially stable companies. To serve Jabil's new strategy, Mitchell placed priority on finding a way to reliably vet the startups' creditworthiness to avoid bad debt. The third-party credit rating agencies Jabil used could only provide a score for large companies with accessible financial information and history. Mitchell's computer pinged with a calendar reminder-it was almost time for her next update meeting with her data science team. So far, their model had achieved an accuracy rate of 86%. This was promising but not yet good enough. Mitchell knew they would have to address this-and soon. The faster a way to test their financial viability could be found, the sooner Jabil could partner with them and profit from them. Mitchell wondered what impact adding more quantitative and qualitative data would have on the creditworthiness prediction model. She knew it could lead to higher accuracy, or it could lead to a redesign, which meant more time and resources. The model had to be accurate, explainable, and auditable. Was it possible to create this model internally at Jabil?

Research paper thumbnail of Polymer coated fat crystals as oil structuring agents: Fabrication and oil-structuring properties

Food Hydrocolloids, 2021

Abstract Oleogel has attracted the interest of food scientists and the food industry as an intere... more Abstract Oleogel has attracted the interest of food scientists and the food industry as an interesting alternative for solid fat in food products. Certain hydrophilic polymers, such as gelatin (GTA), are known to form gel structures in water, but fail to structure apolar solvents due to incompatibility. The hydrophilic polymers can only be introduced into an apolar solvent using an indirect approach. In our approach, GTA acted as a stabilizer of oil-in-water emulsions. During emulsification, GTA adsorbed at the interface, forming a polymer protective layer. Upon cooling, crystallisation of fully hydrogenated rapeseed oil (FHRO), as the oil droplets, fixed the polymer layer onto the droplets. Subsequently, the crystallised fat droplets were separated from the continuous water phase through creaming, and then subjected to drying. The dried fat droplets, fat capsules, exhibited spherical shape with D(3,2) at 6.7 ± 3.3 μm based on the microscopy and laser light scattering analyses. Interestingly, confocal laser scanning microscopy (CLSM) confirmed the location of the GTA layer on the surface of the fat capsules. Moreover, diffraction and thermal analyses showed similar properties between FHRO and GTA fat capsules, thus indicating that FHRO independently crystallised without being affected by the fabrication techniques and GTA. Subsequently, the fat capsules were tested as an oil structuring agent by employing two different approaches to form composite oleogels and particle-based oleogels. The amplitude sweep test showed that all oleogels behaved in a solid-like manner. The shear modulus of oleogels prepared from fat capsules was higher than the reference oleogel, regardless of the preparation approach. Electron microscopy confirmed the formation of composite oleogel and particle-based oleogels by the fat capsules as the structuring building blocks in the respective oleogels. In the oleogels, GTA acted as a filler in GTA-oleogel (GTA1) and as a surface polymer that interconnected the fat capsules in particle-based oleogel (GTA2) and particle-based added water oleogel (GTA3). Ultimately, we have shown the formation of FHRO coated with hydrocolloid, which can potentially act as a functional material for structuration and delivery vehicles.

Research paper thumbnail of Fat crystallization of blends of palm oil and anhydrous milk fat: A comparison between static and dynamic-crystallization

Food Research International, 2020

The application of dynamic-crystallization (a combination of shear with rapid cooling) often play... more The application of dynamic-crystallization (a combination of shear with rapid cooling) often plays an important role in the production of industrial fat-based products such as shortenings/margarines but has been rarely reported. In this study, three blends of palm oil (PO) with anhydrous milk fat (AMF) (0, 25 and 50% AMF, w/w) were rapidly crystallized under static (using freezer) and dynamic conditions (using a benchtop scraped surface heat exchanger). Various techniques including differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarized light microscopy (PLM), rheology and texture analysis were applied to investigate physicochemical properties of fat blends as well as their crystal morphology upon the long-term storage (4 weeks) at 5 °C and 15 °C. The results revealed that high cooling rate of dynamic-crystallization not only affected melting behavior of fat blends but also prevented the polymorphic transformation from β' to β crystals. Besides, the application of shear during fat crystallization helped to improve significantly the gel strength of produced shortenings. Although post-crystallization of low melting triacylglycerols (TAGs) occurred for all produced shortenings during storage at 5 °C which was accompanying with a firmness increase, it was more considerable for samples owning higher AMF content. Moreover, this phenomenon promoted the sintering as well as Ostwald ripening between fat crystals of dynamic-crystallized fat blends resulting in the formation of unwanted large aggregates (or granular crystals) with the size ranging from 100 to 500 μm.

Research paper thumbnail of Granular Crystals in Palm Oil Based Shortening/Margarine: A Review

Crystal Growth & Design, 2019

Research paper thumbnail of Low-Calorie Sugars Produced by Lactic Acid Bacteria

Biotechnology of Lactic Acid Bacteria

Page 1. 193 Low - Calorie Sugars Produced by Lactic Acid Bacteria Gino Vrancken , Tom Rimaux , Lu... more Page 1. 193 Low - Calorie Sugars Produced by Lactic Acid Bacteria Gino Vrancken , Tom Rimaux , Luc De Vuyst , and Fernanda Mozzi ... In addition, various yeasts and bacteria are able to synthesize sorbitol (Silveira and Jonas 2002 ; Jonas and Silveira 2004 ). ...

Research paper thumbnail of Kinetic analysis of growth and sugar consumption by Lactobacillus fermentum IMDO 130101 reveals adaptation to the acidic sourdough ecosystem

International Journal of Food Microbiology, 2008

Research paper thumbnail of Environmental pH determines citrulline and ornithine release through the arginine deiminase pathway in Lactobacillus fermentum IMDO 130101

International Journal of Food Microbiology, 2009

Research paper thumbnail of Biodiversity, ecological determinants, and metabolic exploitation of sourdough microbiota

Food Microbiology, 2009

Sourdough is a microbial ecosystem of lactic acid bacteria (LAB) and yeasts in a matrix of mainly... more Sourdough is a microbial ecosystem of lactic acid bacteria (LAB) and yeasts in a matrix of mainly cereal flour and water. Culture-dependent and culture-independent microbiological analysis together with metabolite target analyses of different sourdoughs enabled to understand this complex fermentation process. It is difficult to link the species diversity of the sourdough microbiota with the (geographical) type of sourdough and the flour used, although the type and quality of the latter is the main source of autochthonous LAB in spontaneous sourdough fermentations and plays a key role in establishing stable microbial consortia within a short time. Carbohydrate fermentation targeted towards maltose catabolism, the use of external alternative electron acceptors, amino acid transamination reactions, and/or the arginine deiminase pathway are metabolic activities that favour energy production, cofactor (re)cycling, and/or tolerance towards acid stress, and hence contribute to the competitiveness and dominance of certain species of LAB found in sourdoughs. Also, microbial interactions play an important role. The availability of genome sequences for several LAB species that are of importance in sourdough as well as technological advances in the fields of functional genomics, transcriptomics, and proteomics enable new approaches to study sourdough fermentations beyond the single species level and will allow an integral analysis of the metabolic activities and interactions taking place in sourdough. Finally, the implementation of selected starter cultures in sourdough technology is of pivotal importance for the industrial production of sourdoughs to be used as flavour carrier, texture-improving, or health-promoting dough ingredient.

Research paper thumbnail of The kinetics of the arginine deiminase pathway in the meat starter culture Lactobacillus sakei CTC 494 are pH-dependent

Research paper thumbnail of The arginine deiminase pathway of Lactobacillus fermentum IMDO 130101 responds to growth under stress conditions of both temperature and salt

Food Microbiology, 2009

The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (... more The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (LAB) convert arginine into ornithine via citrulline while producing ammonia and ATP, thereby coping with acid stress and gaining an energetic advantage. Lactobacillus fermentum IMDO 130101, an isolate from a spontaneous laboratory rye sourdough, possesses an ADI pathway which is modulated by environmental pH. In the present study, a broader view of the activity of the ADI pathway in response to growth under two other commonly encountered stress factors, temperature and added salt, was obtained. In both cases, an increase in ornithine production was observed as a response to growth under both temperature and salt stress conditions. Biokinetic parameters were obtained to describe the kinetics of the ADI pathway as a function of temperature and added salt. The arginine conversion rate increased as a function of added NaCl concentrations but was hardly affected by temperature. In addition, arginineinto-citrulline conversion rate was not affected by temperature but increased with increasing NaCl concentrations. Citrulline-into-ornithine conversion rate increased with increasing temperature, while it dropped to zero with added salt. These findings suggest a more pronounced adaptation of the strain through the ADI pathway to added salt, as compared with different constant temperatures. Furthermore, these results suggest that the ADI pathway in L. fermentum IMDO 130101 is active in adapting to nonoptimal growth conditions.

Research paper thumbnail of Expression of the Arginine Deiminase Pathway Genes in Lactobacillus sakei Is Strain Dependent and Is Affected by the Environmental pH

Applied and Environmental Microbiology, 2012

ABSTRACTThe adaptation ofLactobacillus sakeito a meat environment is reflected in its metabolic p... more ABSTRACTThe adaptation ofLactobacillus sakeito a meat environment is reflected in its metabolic potential. For instance, the ability to utilize arginine through the arginine deiminase (ADI) pathway, resulting in additional ATP, represents a competitive benefit. InL. sakeiCTC 494, thearcoperon (arcABCTDR) shows the same gene order and organization as that inL. sakei23K, the genome sequence of which is known. However, differences in relative gene expression were found, and these seemed to be optimal in different growth phases, namely, the highest relative gene expression level was in the end exponential growth phase in the case ofL. sakeiCTC 494 and in the mid-exponential growth phase ofL. sakei23K. Also, the environmental pH influenced the relative expression level of thearcoperon, as shown forL. sakeiCTC 494, with the highest relative expression level occurring at the optimal pH for growth (pH 6.0). Deviations from this optimal pH (pH 5.0 and pH 7.0) resulted in an overall decline o...

Research paper thumbnail of The Pentose Moiety of Adenosine and Inosine Is an Important Energy Source for the Fermented-Meat Starter Culture Lactobacillus sakei CTC 494

Applied and Environmental Microbiology, 2011

ABSTRACTThe genome sequence ofLactobacillus sakei23K has revealed that the speciesL. sakeiharbors... more ABSTRACTThe genome sequence ofLactobacillus sakei23K has revealed that the speciesL. sakeiharbors several genes involved in the catabolism of energy sources other than glucose in meat, such as glycerol, arginine, and nucleosides. In this study, a screening of 15L. sakeistrains revealed that arginine, inosine, and adenosine could be used as energy sources by all strains. However, no glycerol catabolism occurred in any of theL. sakeistrains tested. A detailed kinetic analysis of inosine and adenosine catabolism in the presence of arginine byL. sakeiCTC 494, a fermented-meat starter culture, was performed. It showed that nucleoside catabolism occurred as a mixed-acid fermentation in a pH range (pH 5.0 to 6.5) relevant for sausage fermentation. This resulted in the production of a mixture of acetic acid, formic acid, and ethanol from ribose, while the nucleobase (hypoxanthine and adenine in the case of fermentations with inosine and adenosine, respectively) was excreted into the medium ...

Research paper thumbnail of A putative transport protein is involved in citrulline excretion and re-uptake during arginine deiminase pathway activity by Lactobacillus sakei

Research in Microbiology, 2013

Arginine conversion through the arginine deiminase (ADI) pathway is a common metabolic trait of L... more Arginine conversion through the arginine deiminase (ADI) pathway is a common metabolic trait of Lactobacillus sakei which is ascribed to an arc operon and which inquisitively involves citrulline excretion and re-uptake. The aim of this study was to verify whether a putative transport protein (encoded by the PTP gene) plays a role in citrulline-into-ornithine conversion by L. sakei strains. This was achieved through a combination of fermentation experiments, gene expression analysis via quantitative real-time reverse transcription PCR (RT-qPCR) and construction of a PTP knock-out mutant. Expression of the PTP gene was modulated by environmental pH and was highest in the end-exponential or mid-exponential growth phase for L. sakei strains CTC 494 and 23K, respectively. In contrast to known genes of the arc operon, the PTP gene showed low expression at pH 7.0, in agreement with the finding that citrulline-into-ornithine conversion is inhibited at this pH. The presence of additional energy sources also influenced ADI pathway activity, in particular by decreasing citrulline-into-ornithine conversion. Further insight into the functionality of the PTP gene was obtained with a knock-out mutant of L. sakei CTC 494 impaired in the PTP gene, which displayed inhibition in its ability to convert extracellular citrulline into ornithine. In conclusion, results indicated that the PTP gene may putatively encode a citrulline/ornithine antiporter.

Research paper thumbnail of Adaptation of Lactobacillus fermentum IMDO 130101 to the sourdough ecosystem through mannitol production and arginine conversion

Research paper thumbnail of The effect of cooling on crystallization and physico-chemical properties of puff pastry shortening made of palm oil and anhydrous milk fat blends

Journal of Food Engineering, 2021

Assessing the creditworthiness of technology startups could be a game-changer for Jabil's custome... more Assessing the creditworthiness of technology startups could be a game-changer for Jabil's customer expansion strategy. Candy Mitchell, Information Technology Director at Jabil Inc., sank into her desk chair and looked out the window pensively. She had just finished reading a report from her team of data scientists about a predictive model they had created. She saw huge potential in this model as a potential solution to power Jabil's customer growth strategy. Part of the strategy was to engage with technology startup companies to be their partner of choice from ideation to supply chain management. Working with technology startups would be new for Jabil and could create huge returns (when one of those technology startups took off, so would Jabil). Typical customers for Jabil (a manufacturing solutions provider that delivers comprehensive design, manufacturing, supply chain and product management services) ranged from FORTUNE® 500s to governments. Mitchell knew how risky startup customers could be, and Jabil only wanted to work with financially stable companies. To serve Jabil's new strategy, Mitchell placed priority on finding a way to reliably vet the startups' creditworthiness to avoid bad debt. The third-party credit rating agencies Jabil used could only provide a score for large companies with accessible financial information and history. Mitchell's computer pinged with a calendar reminder-it was almost time for her next update meeting with her data science team. So far, their model had achieved an accuracy rate of 86%. This was promising but not yet good enough. Mitchell knew they would have to address this-and soon. The faster a way to test their financial viability could be found, the sooner Jabil could partner with them and profit from them. Mitchell wondered what impact adding more quantitative and qualitative data would have on the creditworthiness prediction model. She knew it could lead to higher accuracy, or it could lead to a redesign, which meant more time and resources. The model had to be accurate, explainable, and auditable. Was it possible to create this model internally at Jabil?

Research paper thumbnail of Polymer coated fat crystals as oil structuring agents: Fabrication and oil-structuring properties

Food Hydrocolloids, 2021

Abstract Oleogel has attracted the interest of food scientists and the food industry as an intere... more Abstract Oleogel has attracted the interest of food scientists and the food industry as an interesting alternative for solid fat in food products. Certain hydrophilic polymers, such as gelatin (GTA), are known to form gel structures in water, but fail to structure apolar solvents due to incompatibility. The hydrophilic polymers can only be introduced into an apolar solvent using an indirect approach. In our approach, GTA acted as a stabilizer of oil-in-water emulsions. During emulsification, GTA adsorbed at the interface, forming a polymer protective layer. Upon cooling, crystallisation of fully hydrogenated rapeseed oil (FHRO), as the oil droplets, fixed the polymer layer onto the droplets. Subsequently, the crystallised fat droplets were separated from the continuous water phase through creaming, and then subjected to drying. The dried fat droplets, fat capsules, exhibited spherical shape with D(3,2) at 6.7 ± 3.3 μm based on the microscopy and laser light scattering analyses. Interestingly, confocal laser scanning microscopy (CLSM) confirmed the location of the GTA layer on the surface of the fat capsules. Moreover, diffraction and thermal analyses showed similar properties between FHRO and GTA fat capsules, thus indicating that FHRO independently crystallised without being affected by the fabrication techniques and GTA. Subsequently, the fat capsules were tested as an oil structuring agent by employing two different approaches to form composite oleogels and particle-based oleogels. The amplitude sweep test showed that all oleogels behaved in a solid-like manner. The shear modulus of oleogels prepared from fat capsules was higher than the reference oleogel, regardless of the preparation approach. Electron microscopy confirmed the formation of composite oleogel and particle-based oleogels by the fat capsules as the structuring building blocks in the respective oleogels. In the oleogels, GTA acted as a filler in GTA-oleogel (GTA1) and as a surface polymer that interconnected the fat capsules in particle-based oleogel (GTA2) and particle-based added water oleogel (GTA3). Ultimately, we have shown the formation of FHRO coated with hydrocolloid, which can potentially act as a functional material for structuration and delivery vehicles.

Research paper thumbnail of Fat crystallization of blends of palm oil and anhydrous milk fat: A comparison between static and dynamic-crystallization

Food Research International, 2020

The application of dynamic-crystallization (a combination of shear with rapid cooling) often play... more The application of dynamic-crystallization (a combination of shear with rapid cooling) often plays an important role in the production of industrial fat-based products such as shortenings/margarines but has been rarely reported. In this study, three blends of palm oil (PO) with anhydrous milk fat (AMF) (0, 25 and 50% AMF, w/w) were rapidly crystallized under static (using freezer) and dynamic conditions (using a benchtop scraped surface heat exchanger). Various techniques including differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarized light microscopy (PLM), rheology and texture analysis were applied to investigate physicochemical properties of fat blends as well as their crystal morphology upon the long-term storage (4 weeks) at 5 °C and 15 °C. The results revealed that high cooling rate of dynamic-crystallization not only affected melting behavior of fat blends but also prevented the polymorphic transformation from β' to β crystals. Besides, the application of shear during fat crystallization helped to improve significantly the gel strength of produced shortenings. Although post-crystallization of low melting triacylglycerols (TAGs) occurred for all produced shortenings during storage at 5 °C which was accompanying with a firmness increase, it was more considerable for samples owning higher AMF content. Moreover, this phenomenon promoted the sintering as well as Ostwald ripening between fat crystals of dynamic-crystallized fat blends resulting in the formation of unwanted large aggregates (or granular crystals) with the size ranging from 100 to 500 μm.

Research paper thumbnail of Granular Crystals in Palm Oil Based Shortening/Margarine: A Review

Crystal Growth & Design, 2019

Research paper thumbnail of Low-Calorie Sugars Produced by Lactic Acid Bacteria

Biotechnology of Lactic Acid Bacteria

Page 1. 193 Low - Calorie Sugars Produced by Lactic Acid Bacteria Gino Vrancken , Tom Rimaux , Lu... more Page 1. 193 Low - Calorie Sugars Produced by Lactic Acid Bacteria Gino Vrancken , Tom Rimaux , Luc De Vuyst , and Fernanda Mozzi ... In addition, various yeasts and bacteria are able to synthesize sorbitol (Silveira and Jonas 2002 ; Jonas and Silveira 2004 ). ...

Research paper thumbnail of Kinetic analysis of growth and sugar consumption by Lactobacillus fermentum IMDO 130101 reveals adaptation to the acidic sourdough ecosystem

International Journal of Food Microbiology, 2008

Research paper thumbnail of Environmental pH determines citrulline and ornithine release through the arginine deiminase pathway in Lactobacillus fermentum IMDO 130101

International Journal of Food Microbiology, 2009

Research paper thumbnail of Biodiversity, ecological determinants, and metabolic exploitation of sourdough microbiota

Food Microbiology, 2009

Sourdough is a microbial ecosystem of lactic acid bacteria (LAB) and yeasts in a matrix of mainly... more Sourdough is a microbial ecosystem of lactic acid bacteria (LAB) and yeasts in a matrix of mainly cereal flour and water. Culture-dependent and culture-independent microbiological analysis together with metabolite target analyses of different sourdoughs enabled to understand this complex fermentation process. It is difficult to link the species diversity of the sourdough microbiota with the (geographical) type of sourdough and the flour used, although the type and quality of the latter is the main source of autochthonous LAB in spontaneous sourdough fermentations and plays a key role in establishing stable microbial consortia within a short time. Carbohydrate fermentation targeted towards maltose catabolism, the use of external alternative electron acceptors, amino acid transamination reactions, and/or the arginine deiminase pathway are metabolic activities that favour energy production, cofactor (re)cycling, and/or tolerance towards acid stress, and hence contribute to the competitiveness and dominance of certain species of LAB found in sourdoughs. Also, microbial interactions play an important role. The availability of genome sequences for several LAB species that are of importance in sourdough as well as technological advances in the fields of functional genomics, transcriptomics, and proteomics enable new approaches to study sourdough fermentations beyond the single species level and will allow an integral analysis of the metabolic activities and interactions taking place in sourdough. Finally, the implementation of selected starter cultures in sourdough technology is of pivotal importance for the industrial production of sourdoughs to be used as flavour carrier, texture-improving, or health-promoting dough ingredient.

Research paper thumbnail of The kinetics of the arginine deiminase pathway in the meat starter culture Lactobacillus sakei CTC 494 are pH-dependent

Research paper thumbnail of The arginine deiminase pathway of Lactobacillus fermentum IMDO 130101 responds to growth under stress conditions of both temperature and salt

Food Microbiology, 2009

The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (... more The arginine deiminase (ADI) pathway is a means by which certain sourdough lactic acid bacteria (LAB) convert arginine into ornithine via citrulline while producing ammonia and ATP, thereby coping with acid stress and gaining an energetic advantage. Lactobacillus fermentum IMDO 130101, an isolate from a spontaneous laboratory rye sourdough, possesses an ADI pathway which is modulated by environmental pH. In the present study, a broader view of the activity of the ADI pathway in response to growth under two other commonly encountered stress factors, temperature and added salt, was obtained. In both cases, an increase in ornithine production was observed as a response to growth under both temperature and salt stress conditions. Biokinetic parameters were obtained to describe the kinetics of the ADI pathway as a function of temperature and added salt. The arginine conversion rate increased as a function of added NaCl concentrations but was hardly affected by temperature. In addition, arginineinto-citrulline conversion rate was not affected by temperature but increased with increasing NaCl concentrations. Citrulline-into-ornithine conversion rate increased with increasing temperature, while it dropped to zero with added salt. These findings suggest a more pronounced adaptation of the strain through the ADI pathway to added salt, as compared with different constant temperatures. Furthermore, these results suggest that the ADI pathway in L. fermentum IMDO 130101 is active in adapting to nonoptimal growth conditions.

Research paper thumbnail of Expression of the Arginine Deiminase Pathway Genes in Lactobacillus sakei Is Strain Dependent and Is Affected by the Environmental pH

Applied and Environmental Microbiology, 2012

ABSTRACTThe adaptation ofLactobacillus sakeito a meat environment is reflected in its metabolic p... more ABSTRACTThe adaptation ofLactobacillus sakeito a meat environment is reflected in its metabolic potential. For instance, the ability to utilize arginine through the arginine deiminase (ADI) pathway, resulting in additional ATP, represents a competitive benefit. InL. sakeiCTC 494, thearcoperon (arcABCTDR) shows the same gene order and organization as that inL. sakei23K, the genome sequence of which is known. However, differences in relative gene expression were found, and these seemed to be optimal in different growth phases, namely, the highest relative gene expression level was in the end exponential growth phase in the case ofL. sakeiCTC 494 and in the mid-exponential growth phase ofL. sakei23K. Also, the environmental pH influenced the relative expression level of thearcoperon, as shown forL. sakeiCTC 494, with the highest relative expression level occurring at the optimal pH for growth (pH 6.0). Deviations from this optimal pH (pH 5.0 and pH 7.0) resulted in an overall decline o...

Research paper thumbnail of The Pentose Moiety of Adenosine and Inosine Is an Important Energy Source for the Fermented-Meat Starter Culture Lactobacillus sakei CTC 494

Applied and Environmental Microbiology, 2011

ABSTRACTThe genome sequence ofLactobacillus sakei23K has revealed that the speciesL. sakeiharbors... more ABSTRACTThe genome sequence ofLactobacillus sakei23K has revealed that the speciesL. sakeiharbors several genes involved in the catabolism of energy sources other than glucose in meat, such as glycerol, arginine, and nucleosides. In this study, a screening of 15L. sakeistrains revealed that arginine, inosine, and adenosine could be used as energy sources by all strains. However, no glycerol catabolism occurred in any of theL. sakeistrains tested. A detailed kinetic analysis of inosine and adenosine catabolism in the presence of arginine byL. sakeiCTC 494, a fermented-meat starter culture, was performed. It showed that nucleoside catabolism occurred as a mixed-acid fermentation in a pH range (pH 5.0 to 6.5) relevant for sausage fermentation. This resulted in the production of a mixture of acetic acid, formic acid, and ethanol from ribose, while the nucleobase (hypoxanthine and adenine in the case of fermentations with inosine and adenosine, respectively) was excreted into the medium ...

Research paper thumbnail of A putative transport protein is involved in citrulline excretion and re-uptake during arginine deiminase pathway activity by Lactobacillus sakei

Research in Microbiology, 2013

Arginine conversion through the arginine deiminase (ADI) pathway is a common metabolic trait of L... more Arginine conversion through the arginine deiminase (ADI) pathway is a common metabolic trait of Lactobacillus sakei which is ascribed to an arc operon and which inquisitively involves citrulline excretion and re-uptake. The aim of this study was to verify whether a putative transport protein (encoded by the PTP gene) plays a role in citrulline-into-ornithine conversion by L. sakei strains. This was achieved through a combination of fermentation experiments, gene expression analysis via quantitative real-time reverse transcription PCR (RT-qPCR) and construction of a PTP knock-out mutant. Expression of the PTP gene was modulated by environmental pH and was highest in the end-exponential or mid-exponential growth phase for L. sakei strains CTC 494 and 23K, respectively. In contrast to known genes of the arc operon, the PTP gene showed low expression at pH 7.0, in agreement with the finding that citrulline-into-ornithine conversion is inhibited at this pH. The presence of additional energy sources also influenced ADI pathway activity, in particular by decreasing citrulline-into-ornithine conversion. Further insight into the functionality of the PTP gene was obtained with a knock-out mutant of L. sakei CTC 494 impaired in the PTP gene, which displayed inhibition in its ability to convert extracellular citrulline into ornithine. In conclusion, results indicated that the PTP gene may putatively encode a citrulline/ornithine antiporter.