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[Fermentation of a high-protein plant biomass by introduction of lactic acid bacteria].

Lactic acid bacteria displaying increased ability to produce lactic acid, medium proteolytic activity, and tolerance to osmotic stress were isolated under selective conditions from phyllosphere and rhizosphere of registered and raised cultivars of legumes. Lactic fermentation of poorly ensilable leguminous plants (red clover and Caucasian goat's rue) was performed by introduction of rifampin-resistant homofermenting representatives of the genus Lactobacillus (selected according to a set of technologically important characteristics). The results demonstrate that introduction of active local strains of lactobacteria, as well as the collection strain Lactobacillus plantarum BS 933, enhances activation of ensiling and increases the quality of fodder, as assessed according to the standard criteria (a decrease in pH of the medium, the ratio of lactic acid to fatty acid homologues, and the composition of silage microflora).

Biomass↗
PubMed2001

Biosynthesis, characterisation, and design of bacterial exopolysaccharides from lactic acid bacteria.

Lactic acid bacteria (LAB) are characterised by their conversion of a large proportion of their carbon feed, fermentable sugars, to lactic acid. However, in addition to lactic acid production, the LAB are able to divert a small proportion of fermentable sugars towards the biosynthesis of exopolysaccharides (EPSs) that are independent of the cell surface and cell wall material. These microbial EPSs when suspended or dissolved in aqueous solution provide thickening and gelling properties, and, as such, there is great interest in using EPSs from food grade microorganisms (such as the LAB that are traditionally used for food fermentations) for use as thickening agents. The current review includes a brief summary of the recent literature describing features of the biosynthetic pathways leading to EPS production. Many aspects of EPS biosynthesis in LAB are still not fully understood and a number of inferences are made regarding the similarity of the pathway to those involved in the synthesis of other cell polysaccharides, e.g., cell wall components. The main body of the review will cover practical aspects concerned with the isolation and characterisation of EPS structures. In the last couple of years, a substantial number of structures have been published and a summary of the common elements of these structures is included as is a suggestion for a system for representing structures. A brief highlight of the attempts that are being made to design 'tailor'-made polysaccharides using genetic modification and control of metabolic flux is presented.

Journal Article↗
PubMed2006

Impact of chemical components of organic wastes on L(+)-lactic acid production.

Lactic acid production from several organic wastes that had different chemical compositions was examined, and the factors strongly impacting yield were determined. The bioconversion of sugars to lactic acid was affected by the ratio of total sugars to total nitrogen content (the TS/N ratio), and was improved by nitrogen supplementation to adjust the TS/N ratio > or =10. Lactic acid yield was also affected by the fermentable sugars contents, i.e. various oligosaccharides constituted of mainly C6-sugars. The estimation of the fermentable sugars was determined by the total sugars content in starchy materials, such as kitchen wastes, but in lignocellulosic materials, the estimation was affected by the hemicellulose contents. The estimation model of the fermentable sugars was proposed by multivariate analysis using organic components as variables.

Carbohydrate Metabolism↗
PubMed2003

Highly active antiretroviral therapy (HAART)-associated lactic acidosis: in vitro effects of combination of nucleoside analogues and protease inhibitors on mitochondrial function and lactic acid production.

Lactic acidosis is a rare but potentially life-threatening and poorly understood sequelae among HIV-infected patients on highly active antiretroviral therapy (HAART). Mitochondrial DNA depletion and inhibition of respiratory complexes have been hypothesized to be involved in HAART-associated lactic acidosis. Although mitochondrial toxicity and increased plasma lactates are associated with long-term exposure to nucleoside analogue reverse transcriptase inhibitors (NRTI), reports of lactic acidosis are now emerging among HIV-infected patients exposed to combination therapy that includes not only NRTI but also protease inhibitors (PI). We therefore investigated the effects of clinically relevant NRTI and PI combinations on mitochondrial membrane potential, uncoupling of mitochondrial respiration from oxidative phosphorylation and lactic acid production. Our study demonstrated that treatment of HepG2 cells with a combination of nucleoside analogues and PI, decreased mitochondrial membrane potential (delta psi m) within 24 hr, followed by increased lactic acid production after 9 days of treatment. However, loss of delta psi m and increased lactates were not associated with mitochondrial uncoupling or ATP production. Our findings suggested that not only NRTI but also PI are capable of increasing lactic acid production in vitro, and probably involve early biochemical changes in mitochondrial function such as loss of mitochondrial membrane potential.

Acidosis, Lactic↗
PubMed1997

Controlled overproduction of proteins by lactic acid bacteria.

Lactic acid bacteria are widely used in industrial food fermentations, contributing to flavour, texture and preservation of the fermented products. Here we describe recent advances in the development of controlled gene expression systems, which allow the regulated overproduction of any desirable protein by lactic acid bacteria. Some systems benefit from the fact that the expression vectors, marker genes and inducing factors can be used directly in food applications since they are all derived from food-grade lactic acid bacteria. These systems have also been employed for the development of autolytic bacteria, suitable for various industrial applications.

Biotechnology↗
PubMed2002

Steady-state measurements of lactic acid production in a wild-type and a putative D-lactic acid dehydrogenase-negative mutant of Zymomonas mobilis: influence of glycolytic flux.

This work represents a continuation of our investigation into environmental conditions that promote lactic acid synthesis by Zymomonas mobilis. The characteristic near theoretical yield of ethanol from glucose by Z. mobilis can be compromised by the synthesis of D- and L-lactic acid. The production of lactic acid is exacerbated by the following conditions: pH 6.0, yeast extract, and reduced growth rate. At a specific growth rate of 0.048/h, the average yield of DL-lactate from glucose in a yeast extract-based medium at pH 6.0 was 0.15 g/g. This represents a reduction in ethanol yield of about 10% relative to the yield at a growth rate of 0.15/h. Very little lactic acid was produced at pH 5.0 or using a defined salts medium (without yeast extract) Under permissive and comparable culture conditions, a tetracycline-resistant, D-ldh negative mutant produced about 50% less lactic acid than its parent strain Zm ATCC 39676. D-lactic acid was detected in the cell-free spent fermentation medium of the mutant, but this could be owing to the presence of a racemase enzyme. Under the steady-state growth conditions provided by the chemostat, the specific rate of glucose consumption was altered at a constant growth rate of 0.075/h. Shifting from glucose-limited to nitrogen-limited growth, or increasing the temperature, caused an increase in the specific rate of glucose catabolism. There was good correlation between an increase in glycolytic flux and a decrease in lactic acid yield from glucose. This study points to a mechanistic link between the glycolytic flux and the control of end-product glucose metabolism. Implications of reduced glycolytic flux in pentose-fermenting recombinant Z. mobilis strains, relative to increased byproduct synthesis, is discussed.

Fermentation↗
PubMed2004

Production of L-lactic acid from a mixture of xylose and glucose by co-cultivation of lactic acid bacteria.

The production of optically pure lactic acid in a high yield from xylose or a mixture of xylose and glucose, which is a model hydrolysate of lignocellulose, is described. In a single cultivation, Enterococcus casseliflavus produced 38 g/l of lactic acid with an optical purity of 96% enantiomeric excess (ee) and 6.4 g/l of acetic acid from 50 g/l of xylose when MRS medium was used. When a mixture of 50 g/l of xylose and 100 g/l of glucose was used as the carbon source in a cultivation of E. casseliflavus alone, glucose was converted to lactic acid in the early phase of the cultivation but xylose was hardly consumed. In a co-cultivation where E. casseliflavus and Lactobacillus casei specific for glucose were simultaneously inoculated, little or no lactic acid was produced after the glucose was almost consumed. A co-cultivation with two-stage inoculation (in which E. casseliflavus was added at a cultivation time of 40 h after L. casei cells were inoculated) resulted in complete consumption of 50 g/l of xylose and 100 g/l of glucose. In the co-cultivation, 95 g/l of lactic acid with a high optical purity of 96% ee was obtained at 192 h. Such a co-cultivation using two microorganisms specific for each sugar is considered to be one promising cultivation technique for the efficient production of lactic acid from a sugar mixture derived from lignocellulose.

Coculture Techniques↗
PubMed2003

Metabolic pathway engineering in lactic acid bacteria.

Lactic acid bacteria (LAB) display a relatively simple carbon and energy metabolism where the sugar source is converted mainly to lactic acid. In Lactococcus lactis metabolic engineering has been very successful in the re-routing of lactococcal pyruvate metabolism to products other than lactic acid. Current metabolic engineering approaches tend to focus on more complex, biosynthetic pathways leading to end-products that generate a health benefit for the consumer (nutraceuticals). Several examples of research on these minor pathways in L. lactis have illustrated the potential of LAB as producers of these metabolites. Whole genome sequencing efforts and corresponding global technologies will have an impact on metabolic engineering in the future.

Bacterial Proteins↗
PubMed1988

Bacteriocins of lactic acid bacteria.

Lactic acid bacteria produce a variety of antagonistic factors that include metabolic end products, antibiotic-like substances and bactericidal proteins, termed bacteriocins. The range of inhibitory activity by bacteriocins of lactic acid bacteria can be either narrow, inhibiting only those strains that are closely related to the producer organism, or wide, inhibiting a diverse group of Gram-positive microorganisms. The following review will discuss biochemical and genetic aspects of bacteriocins that have been identified and characterized from lactic acid bacteria.

Bacteriocins↗
PubMed1976

Carbohydrate and lipid metabolism during human labor: free fatty acids, glucose, insulin, and lactic acid metabolism during normal and oxytocin-induced labor for postmaturity.

This investigation was performed to study the metabolism of the major body fuels (viz. glucose and free fatty acids), insulin, and lactic acid during the stress of human labor. In addition, the role of the normal placenta in the transport of these substances between mother and the fetus was evaluated by measuring them in the mother and cord blood at delivery. To study possible alterations of this role in the placenta which had exceeded the normal period of gestation, a second comparable group of women had labor induced with oxytocin 16-18 days beyond the expected date of delivery. A dramatic twofold increase in maternal plasma free fatty acids was observed during labor. There was a lesser but definite increase in blood glucose concentrations. No rise in serum insulin levels was noted which coincided with the changes in blood glucose. Lactic acid concentrations during the course of labor were variable from baseline but at delivery, the concentrations rose to very significant levels. Free fatty acids and blood glucose levels were significantly higher in the maternal than in the fetal side. A significantly positive correlation was noted between the maternal and cord blood values except for free fatty acids in the postmature group. No significant difference, nor a correlation was found between the two compartments in the insulin nor lactic acid levels. These results suggest that during human labor free fatty acids are the principal metabolic fuel. This increase in maternal free fatty acids may serve to spare glucose as a metabolic fuel in the fetus. The mechanism responsible for the increase maternal free fatty acid mobilization remains to be determined. It is not possible to discern any consistant alteration in placental function as a consequence of prolonged gestation.

Adolescent↗
PubMed2003

Studies on gynaecological hydrophilic lactic acid preparations, part 6: use of Eudragit E-100 as lactic acid carrier in intravaginal tablets.

Hydrophilic intravaginal tablets based on methylcellulose and containing lactic acid component with Eudragit E-100 undergo swelling in standard conditions. A high flow-limit of the gel that originates from the tablets as well as its dynamic viscosity should allow for the durable dosage form in the vagina. By choosing a 1:1 ratio of lactic acid to Eudragit E-100, it is possible to obtain tablets disintegrating into a gelform at physiological range of 3.8-4.4. An increase in the amount of lactic acid in the complex in relation to the polymer up to 2:1 and 3:1 ratios results in gels with a lower pH. These gels possess an acid reserve that might be ableto neutralise the excess of alkali present in severe vaginal infections.

Administration, Intravaginal↗
PubMed2006

Amphiphilic poly(D,L-lactic acid)/poly(ethylene glycol)/poly(D,L-lactic acid) nanogels for controlled release of hydrophobic drugs.

Photocrosslinked nanogels with a hydrophobic core and hydrophilic shell are successfully fabricated with the goal of obtaining a biocompatible and biodegradable drug carrier for hydrophobic anticancer drugs. These nanogels are composed of amphiphilic triblock copolymers, poly(D,L-lactic acid)/poly(ethylene glycol)/poly(D,L-lactic acid) (PLA-PEG-PLA), with acrylated groups at the end of the PLA segments. The copolymers are synthesized by ring-opening polymerization and possess a low CMC (49.6 mg x L(-1)), which easily helps to form micelles by self-assembly. The acrylated end groups allow the micelles to be photocrosslinked by ultraviolet irradiation, which turn the micelles into nanogels. These nanogels exhibit excellent stability as a suspension in aqueous media at ambient temperature as compared to the micelles. Moreover, the size of the nanogels is easily manipulated in a range of 150 to 250 nm by changing the concentration of crosslinkers, e.g., ethylene glycol dimethacrylate, and ultraviolet light irradiation time. The nanogels achieve a high encapsulation efficiency and offer a steady and long-term release mechanism for the hydrophobic anticancer drug, CPT. It shows that these nanogels are useful for a hydrophobic anticancer drug-carrier system. [pictures: see text] Formation of the PLA-PEG-PLA nanogels.

Biocompatible Materials↗
PubMed2006

Amino acid catabolic pathways of lactic acid bacteria.

Lactic acid bacteria (LAB) constitute a diverse group of Gram positive obligately fermentative microorganisms which include both beneficial and pathogenic strains. LAB generally have complex nutritional requirements and therefore they are usually associated with nutrient-rich environments such as animal bodies, plants and foodstuffs. Amino acids represent an important resource for LAB and their utilization serves a number of physiological roles such as intracellular pH control, generation of metabolic energy or redox power, and resistance to stress. As a consequence, the regulation of amino acid catabolism involves a wide set of both general and specific regulators and shows significant differences among LAB. Moreover, due to their fermentative metabolism, LAB amino acid catabolic pathways in some cases differ significantly from those described in best studied prokaryotic model organisms such as Escherichia coli or Bacillus subtilis. Thus, LAB amino acid catabolism constitutes an interesting case for the study of metabolic pathways. Furthermore, LAB are involved in the production of a great variety of fermented products so that the products of amino acid catabolism are also relevant for the safety and the quality of fermented products.

Alanine↗
PubMed1992

Counter-diffusion of lactose and lactic acid in kappa-carrageenan/locust bean gum gel beads with or without entrapped lactic acid bacteria.

The effective diffusion coefficient (De) and equilibrium partition factor (Kp) for lactose and lactic acid in k-carrageenan (2.75% w/w)/locust bean gum (0.25% w/w) (LBG) gel beads (1.5-2.0 mm diameter), with or without entrapped Lactobacillus casei subsp. casei (L. casei), were determined at 40 degrees C. Results were obtained from transient concentration changes in well-stirred solutions of finite volume in which the beads were suspended. Mathematical models of unsteady-state diffusion into and/or from a sphere and appropriate boundary conditions were used to calculate effective diffusion coefficients of lactose and lactic acid from the best fit of the experimental solute concentration changes. The effective diffusivities of lactose and lactic acid were 5.73 x 10(-10) and 9.96 x 10(-10) m2 s-1, respectively. Furthermore, lactic acid was found to modify gel structure since lactose diffusion characteristics (De and Kp) differed significantly from an earlier study and in the literature. In gel beads heavily colonized with L. casei, the effective diffusion coefficients of lactose and lactic acid were respectively 17% and 24% lower than for cell-free beads. Partition coefficients also confirmed the obstruction effect due to the cells, and decreased from 0.89 to 0.79, and from 0.98 to 0.87, for lactose and lactic acid, respectively. External mass transfer was estimated by an unsteady-state model in infinite volume using the Biot number. The effect of external mass transfer resistance on De results and the data reported in the literature are discussed.

Carrageenan↗
PubMed2004

Effects of peroxyacetic acid, acidified sodium chlorite or lactic acid solutions on the microflora of chilled beef carcasses.

The effects of solutions of 0.02% peroxyacetic acid, acidified 0.16% sodium chlorite, 2% lactic acid and 4% lactic acid on the natural flora of the distal surfaces of pieces of brisket, from chilled beef carcass quarters delivered from two slaughtering plants to a processing plant, were investigated. Peroxyacetic acid and acidified sodium chlorite solutions had little effect on the numbers of aerobes, coliforms or Escherichia coli on meat from one plant, and were less effective than 4% lactic acid for reducing the numbers of bacteria on meat from the other plant. With meat from both plants, treatment of meat with 4% lactic acid and holding for 5 or 60 min at 7+/-1 degrees C before sampling resulted in reductions of all three groups of bacteria by >/=1.5 log unit. Treatment with 2% lactic acid resulted in similar reductions when meat was sampled 5 min after the treatment, but reductions were about 1 log unit when meat was sampled 60 min after the treatment. Treatment of carcass quarters with 4% lactic acid resulted in reductions of bacterial numbers of >/=2 log units at distal surfaces, but </=2 log units at medial surfaces. The findings indicate that the efficacies of antimicrobial solutions may be inconsistent when they are applied to chilled meat from different sources and to different types of meat surface, and that bacteria injured by application of an antimicrobial solution may recover during processing of meat at temperatures about 7 degrees C. However, 4% lactic acid may be generally useful as a decontaminant for chilled, raw meat.

Abattoirs↗