Lactic acid bacteria in dairy food: surface characterization and interactions with food matrix components.

This review gives an overview of the importance of interactions occurring in dairy matrices between Lactic Acid Bacteria and milk components. Dairy products are important sources of biological active compounds of particular relevance to human health. These compounds include immunoglobulins, whey proteins and peptides, polar lipids, and lactic acid bacteria including probiotics. A better understanding of interactions between bioactive components and their delivery matrix may successfully improve their transport to their target site of action. Pioneering research on probiotic lactic acid bacteria has mainly focused on their host effects. However, very little is known about their interaction with dairy ingredients. Such knowledge could contribute to designing new and more efficient dairy food, and to better understand relationships between milk constituents. The purpose of this review is first to provide an overview of the current knowledge about the biomolecules produced on bacterial surface and the composition of the dairy matter. In order to understand how bacteria interact with dairy molecules, adhesion mechanisms are subsequently reviewed with a special focus on the environmental conditions affecting bacterial adhesion. Methods dedicated to investigate the bacterial surface and to decipher interactions between bacteria and abiotic dairy components are also detailed. Finally, relevant industrial implications of these interactions are presented and discussed.

In vitro interactions between probiotic bacteria and milk proteins probed by atomic force microscopy.

Interactions between microbial cells and milk proteins are important for cell location into dairy matrices. In this study, interactions between two probiotic strains, Lactobacillus rhamnosus GG and Lactobacillus rhamnosus GR-1, and milk proteins (micellar casein, native and denatured whey proteins) were studied. The bacterial surface characterization was realized with X-ray photoelectron spectroscopy (XPS) to evaluate surface composition (in terms of proteins, polysaccharides and lipid-like compounds) and electrophoretic mobility that provide information on surface charge of both bacteria and proteins along the 3-7 pH range. In addition, atomic force microscopy (AFM) enabled the identification of specific interactions between bacteria and whey proteins, in contrast to the observed nonspecific interactions with micellar casein. These specific events appeared to be more important for the GG strain than for the GR-1 strain, showing that matrix interaction is strain-specific. Furthermore, our study highlighted that in addition to the nature of the strains, many other factors influence the bacterial interaction with dairy matrix including the nature of the proteins and the pH of the media.

Effect of oxygen on the biosynthesis of flavor compound 3-methylbutanal from leucine catabolism during batch culture in Carnobacterium maltaromaticum LMA 28.

In this study, we demonstrated the effect of different dissolved oxygen concentrations (DOC) on cell growth and intracellular biosynthesis of 3-methylbutanal from leucine catabolism in Carnobacterium maltaromaticum LMA 28 during batch culture. The maximum specific growth rate was obtained in culture when DOC was controlled at 50% of air saturation. The specific consumption rates of glucose and specific production rates of lactate were higher at a DOC at 50 or 90% of air saturation. Carnobacterium maltaromaticum LMA 28 produced high quantities of 3-methylbutanal and 3-methylbutanol during culture with DOC maintained at 90%, suggesting that oxygen had a significant effect of the formation of these flavor compounds. This high formation of flavor compounds in an oxygen-rich environment was attributed to the simultaneous activation and stimulation of both α-ketoacid decarboxylase (KADC) and α-ketoacid dehydrogenase (KADH) pathways. Thus, intracellular biosynthesis of 3-methylbutanal can be controlled by modifying the DOC of the culture or food product during fermentation.

Surface properties of bacteria sensitive and resistant to the class IIa carnobacteriocin Cbn BM1.

AIMS: Class IIa bacteriocins are small antimicrobial peptides synthesized by lactic acid bacteria. The proposed mechanisms of action for class IIa bacteriocins suggest that the physicochemical properties of the target bacterial surface govern the bacteriocin antimicrobial activity. The aim of this study is to decipher the relationship between both sensitivity and resistance to a class IIa bacteriocin, carnobacteriocin BM1 and physicochemical surface properties of bacteria. METHODS AND RESULTS: The study was performed on 18 strains by a microbial adhesion to solvents process and with electrophoretic mobility measurements considering bacteria as soft particles. A large variation in bacterial surface properties is observed among the bacterial populations. Electro-hydrodynamic parameters values appear to be more homogeneous for sensitive strains than for the resistant ones, which can exhibit more extreme values. CONCLUSIONS: Physicochemical surface properties of 18 strains determined show large variations between the strains. However, no direct link between these surface properties and the resistant/sensitive phenotypes of the strains can be stated. SIGNIFICANCE AND IMPACT OF THE STUDY: The surface physicochemical properties tested have a low predictive power to discriminate sensitive or resistant strains when determined at the bacterial population scale.

Short communication: impact of pH and temperature on the acidifying activity of Carnobacterium maltaromaticum.

The acidifying activity of Carnobacterium maltaromaticum LMA28, a strain isolated from French soft cheese, was studied in trypticase soy broth with yeast extract (TSB-YE) medium and in milk. In TSB-YE supplemented with lactose, glucose, or galactose, lactose and glucose were metabolized with a maximum growth rate of 0.32 h(-1) and galactose was not metabolized. During hydrolysis of lactose, the galactose moiety was not excreted. The major product was l(+) lactic acid, with no significant difference in the lactic acid yield. Glucose was not completely metabolized because cell growth stopped when pH values reached an average of 5.0. In sterilized UHT milk, the addition of 1 g/L of YE enhanced its coagulation. Compared with commercial starter lactic acid bacteria such as Lactococcus lactis DSMZ 20481 or Streptococcus thermophilus INRA 302, Carnobacterium maltaromaticum LMA 28 was shown to be a slow acidifying strain. However, in spite of this weak acidifying ability, C. maltaromaticum LMA 28 can sustain low pH values in coculture with Lc. lactis DSMZ 20481 or S. thermophilus INRA 302. The individual and interactive effects of initial pH values (5.2 to 8.0) and incubation temperatures (23 to 37 degrees C) on acidifying activity were studied by response surface methodology. The 3 strains displayed different behaviors depending on pH and temperature. The psychrotrophic lactic acid strain C. maltaromaticum LMA 28 was able to grow at alkaline pH values and during storage conditions. It could be used as a potential ripening flora in soft cheese.

Short communication: Carnobacterium maltaromaticum: the only Carnobacterium species in French ripened soft cheeses as revealed by polymerase chain reaction detection.

The PCR technique using Cb1-Cb2R and species-specific primers was applied to various French soft flowered or washed rind cheeses to identify Carnobacterium species. Thirty cheeses made from cow's, ewe's, or goat's milk (raw or pasteurized), of which 20 were Appellation d'Origine Contrôlée, were analyzed in the autumn and spring. The results revealed that, irrespective of the season, the Carnobacterium genus was initially detected in 5 cheeses and was detected in 5 others after an enrichment period. Polymerase chain reaction results using species-specific primers of Carnobacterium showed that these 10 cheeses contained only the species Carnobacterium maltaromaticum. Six different patterns of fermentation were found, and 3 of the 10 cheeses contained C. maltaromaticum isolates with anti-Listeria activity.

[The back in everyday life]. / Le dos au quotidien.

The adaptation of man to an erect posture is the result of phylogenetic as well as ontogenetic evolution of the spinal structures and is largely responsible for the development of back pain. Apart from the specific conditions of overwork, a large number of physical activities and certain postures maintained over long periods of time can favour the development of back pain. The prevention of benign back pain therefore depends on a re-education of the correct use of the back. This can be performed in the form of individual prevention or in small groups of subjects suffering from back pain in whom a high risk activity can be isolated in order to direct the re-education. Primary prevention can also be considered in subjects not presenting back pain, consisting of a better knowledge of the back and its correct use.