The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the bette...The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the better known products for its contribution to the buttery aroma of dairy products. A lot of documents deal with ways to improve diacetyl concentration in food matrices. Apart from these organoleptic advantages, in a microbial ecosystem, the citrate metabolism gives selective advantages to citrate positive microorganisms. Citrate metabolism allows the LAB to use another carbon source for their growth, withstand acidic conditions and generate a “proton motive force” (PMF). Moreover, the citrate/glucid co-metabolism leads to the fast release of organic compounds known for having bacteriostatic effects. Under specific conditions, the C4?pathway liberates diacetyl which is bacteriostatic. In this review we first describe the citrate metabolism and the enzymes involved in the two homo- and heterofermentative LABLc diacetylactisandLeuconostocspp. Moreover, the way to shift the metabolic pathway toward the production of aromatic compounds is discussed for both of these fermentative types of bacteria. Finally, the selective advantages of citrate metabolism for LAB in complex microbial ecosystems are delineated.展开更多
Natural starters have been extensively used for many centuries to make many different fermented food products from different raw materials: Milk, meat, roots, vegetables, etc. The industrialisation of food production ...Natural starters have been extensively used for many centuries to make many different fermented food products from different raw materials: Milk, meat, roots, vegetables, etc. The industrialisation of food production at the end of the 19th century necessitated the use of regular selected starters to standardize the organoleptic characteristics of the final product. As a consequence, during the 20th century, there was a decline in the use of natural starters in Western countries except in the production of local cheeses or sourdough breads. The beginning of this new millennium has witnessed a deep change in consumer demand, in pursuit of quality, safety and pleasure. In this context, natural starters could, in the future, play an important role in the development of fermented products. However, food producers and researchers have first to cope with fundamental problems in the understanding of these complex ecosystems. The dynamic evolution of the microbial population inside the natural starter (its resilience, its genetic and physiological aptitudes) and the consequences on the product are still partially unknown. This document reviews a broad range of articles concerning the use of natural starters with a specific focus on cheeses and breads, and discusses the major stakes for local food production and the consumption of typical products.展开更多
Yoghurt is fermented milk which results from the exclusive action of <i><span style="font-family:Verdana;">Lactobacillus</span></i> <i><span style="font-family:Verdana;&...Yoghurt is fermented milk which results from the exclusive action of <i><span style="font-family:Verdana;">Lactobacillus</span></i> <i><span style="font-family:Verdana;">delbrueckii</span></i><span style="font-family:Verdana;"> subsp </span><i><span style="font-family:Verdana;">bulgaricus</span></i><span style="font-family:Verdana;"> and </span><i><span style="font-family:Verdana;">Streptococcus</span></i> <i><span style="font-family:Verdana;">thermophilus</span></i><span style="font-family:Verdana;">. However, a disruption of the bacterial growth can lead to significant industrial losses. Currents monitoring methods, based on the checking of the pH during the fermentation step are not always satisfactory. The NeOse Pro system, a portable electronic nose, is a mean to obtain immediately aromatic profiles. In this work, we applied this technology to the yoghurt ecosystem, a highly hydrated product. The profiles obtained allowed us to discriminate yoghurts before and after fermentation. In detail, the discrepancy between the two bacteria cultured alone was slight. It was also the case when we compared different initial bacterial ratios. However, two different mixes of bacteria led to clearly distinguishable profiles. A GC/MS analysis performed on products fermented 7</span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span>h allowed us to explain the detection of acetaldehyde by the stimulation of some captors of the apparatus. NeOse Pro is so convenient to study the fermentation of yogurt.</span></span></span>展开更多
Heat treatment of milk may cause whey proteins and caseins to form aggregates. These soluble and micellar aggregates and their other properties (size, composition, shape, etc.) can affect the techno-functionalities to...Heat treatment of milk may cause whey proteins and caseins to form aggregates. These soluble and micellar aggregates and their other properties (size, composition, shape, etc.) can affect the techno-functionalities to the milk, conferring interesting or negative features depending on the application in dairy industries. In this study, we propose a new approach to characterise those protein aggregates. SDS-agarose electrophoresis is followed by the calculation of a retention factor (Rf) for each protein spot. Rf allows milk aggregates to be compared qualitatively under the same conditions. This method could be transposed to the dairy industry for a better knowledge of the milk subsequent to heat treatment.展开更多
The Lactococcus diversity in cow and goat raw milk was investigated. To do so, a protocol had to be established for the specific enumeration of lactococci. Eight agar media and one control medium were analysed to comp...The Lactococcus diversity in cow and goat raw milk was investigated. To do so, a protocol had to be established for the specific enumeration of lactococci. Eight agar media and one control medium were analysed to compare their proficiency in evaluating the Lactococcus population in raw milk: M17 Nal, Elliker, modified Elliker, PCA + milk, modified KCA, modified Chalmers, Turner, FSDA. The M17 medium was used as reference. Eighteen pure strains were tested on these media for their selectivity towards lactococci: six Lactococcus species or subspecies, three Leuconostoc, three Enterococcus, two Lactobacillus, one Streptococcus thermophilus, one Pseudomonas fluorescens, one Escherichia coli and one Staphylococcus aureus. All these bacteria were chosen for their regular presence in raw milk. The KCA medium proved to be the most selective towards lactococci, on condition that 1) we discriminated the colonies using the catalase test and 2) we subtracted the Enterococcus population counted on BEA. However, it was not possible to separate the Streptococcus from the Lactococcus colonies on KCA. The “Lactococcus-like” population including these two genera was estimated at a mean level of 3.18 log(cfu)/mL and 4.14 log(cfu)/mL in cow and goat raw milk respectively. This is consistent with the data already published.展开更多
The effect of enzymatic crosslinking by microbial transglutaminase on the physico-chemical properties of gelatin-based films incorporated with lysozyme were investigated.Increase in the crosslinking degree of gelatin ...The effect of enzymatic crosslinking by microbial transglutaminase on the physico-chemical properties of gelatin-based films incorporated with lysozyme were investigated.Increase in the crosslinking degree of gelatin with microbial transglutaminase concentration in film-forming suspensions was correlated with a decrease of films thickness.Moreover,the enhancement in crosslinking resulted in a decrease of the solubility in water,as well as of the extent of swelling degree,and of the water vapor permeability of films and in an increase of films tensile strength.The kinetics of release at 4◦C of lysozyme from control non-reticulated films and reticulated films to either sodium acetate buffer,or 2%(w/v)agar gels in direct contact were compared.Interestingly,the kinetics of release of lysozyme were always slower from crosslinked films than from control films.This difference was higher for lysozyme release to agar gels,which was dominated by Fickian diffusion.Enzymatic crosslinking by microbial transglutaminase of gelatin-based films incorporated with lysozyme can thus effectively control the release of this food preservative.展开更多
In this study,the interaction of exopolysaccharides from Leuconostoc mesenteroides P35(EPS-LM)with Escherichia coli heat-labile enterotoxin B-pentamer(LTB)was investigated at different concentrations and temperatures ...In this study,the interaction of exopolysaccharides from Leuconostoc mesenteroides P35(EPS-LM)with Escherichia coli heat-labile enterotoxin B-pentamer(LTB)was investigated at different concentrations and temperatures by using surface plasmon resonance(SPR)and molecular docking approaches.FT-IR spectral analysis together with HPTLC analysis revealing that glucose is the only constitutive monosaccharide of EPS-LM suggests that its structure is composed of dextran withα-D(1→6)glycosidic linkages.SPR analysis revealed the high affinity of EPS-LM for immobilized LTB toxin(KA=(2.05±0.04)×10^(6) mol.L−1 at 37℃).The binding process was spontaneous(ΔG<0),endothermic(ΔH>0),and entropy-driven(ΔS>0)with an increase of KA with temperature.This suggests that EPS-LM-LTB interaction is dominated by hydrophobic forces.The binding affinity of EPS-LM to LTB had negligible dependence on enthalpy(ΔH=0.084 kJ mol−1).Further,molecular docking results suggested the presence of some binding sites of EPS-LM on the LTB through hydrophobic forces(Lys,Asp,Arg,Glu)and also hydrogen bonding(Glu)in the hydrophobic core of LTB.Besides autodock studies,Schiffer-Edmundson helical wheel diagrams of LTB inα-helix domain suggested that LTB hydrophobic core is a highly effective region,which was able to form favorable non-polar interactions of the protein's binding surface(with amino acids residues such as Tyr,Leu,Ile)with EPS-LM.This study provided thus further insights into the interactions between EPS-LM and LTB,suggesting that EPS produced by some LAB,such as EPS produced by Ln.mesenteroides P35 strain are good candidates to inhibit E.coli toxin activity.展开更多
文摘The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the better known products for its contribution to the buttery aroma of dairy products. A lot of documents deal with ways to improve diacetyl concentration in food matrices. Apart from these organoleptic advantages, in a microbial ecosystem, the citrate metabolism gives selective advantages to citrate positive microorganisms. Citrate metabolism allows the LAB to use another carbon source for their growth, withstand acidic conditions and generate a “proton motive force” (PMF). Moreover, the citrate/glucid co-metabolism leads to the fast release of organic compounds known for having bacteriostatic effects. Under specific conditions, the C4?pathway liberates diacetyl which is bacteriostatic. In this review we first describe the citrate metabolism and the enzymes involved in the two homo- and heterofermentative LABLc diacetylactisandLeuconostocspp. Moreover, the way to shift the metabolic pathway toward the production of aromatic compounds is discussed for both of these fermentative types of bacteria. Finally, the selective advantages of citrate metabolism for LAB in complex microbial ecosystems are delineated.
文摘Natural starters have been extensively used for many centuries to make many different fermented food products from different raw materials: Milk, meat, roots, vegetables, etc. The industrialisation of food production at the end of the 19th century necessitated the use of regular selected starters to standardize the organoleptic characteristics of the final product. As a consequence, during the 20th century, there was a decline in the use of natural starters in Western countries except in the production of local cheeses or sourdough breads. The beginning of this new millennium has witnessed a deep change in consumer demand, in pursuit of quality, safety and pleasure. In this context, natural starters could, in the future, play an important role in the development of fermented products. However, food producers and researchers have first to cope with fundamental problems in the understanding of these complex ecosystems. The dynamic evolution of the microbial population inside the natural starter (its resilience, its genetic and physiological aptitudes) and the consequences on the product are still partially unknown. This document reviews a broad range of articles concerning the use of natural starters with a specific focus on cheeses and breads, and discusses the major stakes for local food production and the consumption of typical products.
文摘Yoghurt is fermented milk which results from the exclusive action of <i><span style="font-family:Verdana;">Lactobacillus</span></i> <i><span style="font-family:Verdana;">delbrueckii</span></i><span style="font-family:Verdana;"> subsp </span><i><span style="font-family:Verdana;">bulgaricus</span></i><span style="font-family:Verdana;"> and </span><i><span style="font-family:Verdana;">Streptococcus</span></i> <i><span style="font-family:Verdana;">thermophilus</span></i><span style="font-family:Verdana;">. However, a disruption of the bacterial growth can lead to significant industrial losses. Currents monitoring methods, based on the checking of the pH during the fermentation step are not always satisfactory. The NeOse Pro system, a portable electronic nose, is a mean to obtain immediately aromatic profiles. In this work, we applied this technology to the yoghurt ecosystem, a highly hydrated product. The profiles obtained allowed us to discriminate yoghurts before and after fermentation. In detail, the discrepancy between the two bacteria cultured alone was slight. It was also the case when we compared different initial bacterial ratios. However, two different mixes of bacteria led to clearly distinguishable profiles. A GC/MS analysis performed on products fermented 7</span><span><span><span style="font-family:;" "=""> </span></span></span><span><span><span>h allowed us to explain the detection of acetaldehyde by the stimulation of some captors of the apparatus. NeOse Pro is so convenient to study the fermentation of yogurt.</span></span></span>
文摘Heat treatment of milk may cause whey proteins and caseins to form aggregates. These soluble and micellar aggregates and their other properties (size, composition, shape, etc.) can affect the techno-functionalities to the milk, conferring interesting or negative features depending on the application in dairy industries. In this study, we propose a new approach to characterise those protein aggregates. SDS-agarose electrophoresis is followed by the calculation of a retention factor (Rf) for each protein spot. Rf allows milk aggregates to be compared qualitatively under the same conditions. This method could be transposed to the dairy industry for a better knowledge of the milk subsequent to heat treatment.
基金the RMT(“Réseau Mixte Technologique”)“Fromages de Terroir”the CASDAR project“FloracQ”(Ministère de l’Agriculture et de la Pêche,Chambre d’agriculture du cantal).
文摘The Lactococcus diversity in cow and goat raw milk was investigated. To do so, a protocol had to be established for the specific enumeration of lactococci. Eight agar media and one control medium were analysed to compare their proficiency in evaluating the Lactococcus population in raw milk: M17 Nal, Elliker, modified Elliker, PCA + milk, modified KCA, modified Chalmers, Turner, FSDA. The M17 medium was used as reference. Eighteen pure strains were tested on these media for their selectivity towards lactococci: six Lactococcus species or subspecies, three Leuconostoc, three Enterococcus, two Lactobacillus, one Streptococcus thermophilus, one Pseudomonas fluorescens, one Escherichia coli and one Staphylococcus aureus. All these bacteria were chosen for their regular presence in raw milk. The KCA medium proved to be the most selective towards lactococci, on condition that 1) we discriminated the colonies using the catalase test and 2) we subtracted the Enterococcus population counted on BEA. However, it was not possible to separate the Streptococcus from the Lactococcus colonies on KCA. The “Lactococcus-like” population including these two genera was estimated at a mean level of 3.18 log(cfu)/mL and 4.14 log(cfu)/mL in cow and goat raw milk respectively. This is consistent with the data already published.
文摘The effect of enzymatic crosslinking by microbial transglutaminase on the physico-chemical properties of gelatin-based films incorporated with lysozyme were investigated.Increase in the crosslinking degree of gelatin with microbial transglutaminase concentration in film-forming suspensions was correlated with a decrease of films thickness.Moreover,the enhancement in crosslinking resulted in a decrease of the solubility in water,as well as of the extent of swelling degree,and of the water vapor permeability of films and in an increase of films tensile strength.The kinetics of release at 4◦C of lysozyme from control non-reticulated films and reticulated films to either sodium acetate buffer,or 2%(w/v)agar gels in direct contact were compared.Interestingly,the kinetics of release of lysozyme were always slower from crosslinked films than from control films.This difference was higher for lysozyme release to agar gels,which was dominated by Fickian diffusion.Enzymatic crosslinking by microbial transglutaminase of gelatin-based films incorporated with lysozyme can thus effectively control the release of this food preservative.
基金the Minist`ere des Affaires Etrang`eres(France)and the Ministry of Research,Science and Technology(Iran)for financing double PhD scholarship joint-supervision program between France and Iran for Mojtaba AZARI-ANPARThe authors are indebted to Conseil D´epartemental de l’Ain and Bourg en Bresse Agglom´eration for the financial support of BioDyMIA research unit activities.
文摘In this study,the interaction of exopolysaccharides from Leuconostoc mesenteroides P35(EPS-LM)with Escherichia coli heat-labile enterotoxin B-pentamer(LTB)was investigated at different concentrations and temperatures by using surface plasmon resonance(SPR)and molecular docking approaches.FT-IR spectral analysis together with HPTLC analysis revealing that glucose is the only constitutive monosaccharide of EPS-LM suggests that its structure is composed of dextran withα-D(1→6)glycosidic linkages.SPR analysis revealed the high affinity of EPS-LM for immobilized LTB toxin(KA=(2.05±0.04)×10^(6) mol.L−1 at 37℃).The binding process was spontaneous(ΔG<0),endothermic(ΔH>0),and entropy-driven(ΔS>0)with an increase of KA with temperature.This suggests that EPS-LM-LTB interaction is dominated by hydrophobic forces.The binding affinity of EPS-LM to LTB had negligible dependence on enthalpy(ΔH=0.084 kJ mol−1).Further,molecular docking results suggested the presence of some binding sites of EPS-LM on the LTB through hydrophobic forces(Lys,Asp,Arg,Glu)and also hydrogen bonding(Glu)in the hydrophobic core of LTB.Besides autodock studies,Schiffer-Edmundson helical wheel diagrams of LTB inα-helix domain suggested that LTB hydrophobic core is a highly effective region,which was able to form favorable non-polar interactions of the protein's binding surface(with amino acids residues such as Tyr,Leu,Ile)with EPS-LM.This study provided thus further insights into the interactions between EPS-LM and LTB,suggesting that EPS produced by some LAB,such as EPS produced by Ln.mesenteroides P35 strain are good candidates to inhibit E.coli toxin activity.
