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At least 577 records · Page 32Linked to original sources
PubMed2000

Direct chiral resolution of lactic acid in food products by capillary electrophoresis.

Chiral resolution of native DL-lactic acid was performed by capillary electrophoresis using 2-hydroxypropyl-beta-cyclodextrin as a chiral selector. Various factors affecting chiral resolution, migration time, and peak area of lactic acid were studied. The running conditions for optimum separation of lactic acid were found to be 90 mM phosphate buffer (pH 6.0) containing 240 mM 2-hydroxypropyl-beta-cyclodextrin with an effective voltage of -30 kV at 16 degrees C, using direct detection at 200 nm. In order to enhance the sensitivity, sample injection was done under a pressure of 50 mbar for 200 s. On-line sample concentration was accomplished by sample stacking. With this system, D- and L-lactic acids in food products were analyzed successfully.

Electrophoresis, Capillary↗
PubMed2004

Lactic acid tolerance determined by measurement of intracellular pH of single cells of Candida krusei and Saccharomyces cerevisiae isolated from fermented maize dough.

Strains of Candida krusei and Saccharomyces cerevisiae were grown together at 30 degrees C in MYGP broth, pH 2.5, in the presence of 106.4 mM undissociated lactic acid. The two C. krusei strains investigated grew within 48 h from initial counts of 2 x 10(4) to approximately 10(7) cells/ml whereas the two S. cerevisiae strains investigated survived but did not grow in the presence of 106.4 mM undissociated lactic acid at pH 2.5. To explain the differences in lactic acid tolerance of the two yeast species, we used fluorescence-ratio-imaging microscopy and a perfusion system to determine the short-term intracellular pH (pH(i)) changes in single cells of C. krusei and S. cerevisiae. The changes were investigated both in the presence of low (20.7 mM) and high (106.4 mM) concentrations of undissociated lactic acid. For both the investigated species 20.7 mM undissociated lactic acid did not seem to influence the initial pH(i) which for C. krusei was found to be approximately 8.0 and for S. cerevisiae 6.9-7.5. For both C. krusei strains, perfusion with 106.4 mM undissociated lactic acid induced only weak short-term pH(i) responses with a decrease in pH(i) of less than one pH unit. Contrary, for both strains of S. cerevisiae perfusion with 106.4 mM undissociated lactic acid resulted in a significant decrease in pH(i) from initially 6.9-7.5 to 6.2-6.4 after 1 min and further to a pH(i) of < or = 5.5 after 3 min after which it remained constant. The results obtained show that C. krusei is more resistant to short-term pH(i) changes caused by lactic acid than S. cerevisiae, and this, in turn, may be part of the explanation why C. krusei is more tolerant to lactic acid than S. cerevisiae.

Candida↗
PubMed2002

Kinetic and mechanistic investigations on reductions of aflatoxins by lactic acid.

The kinetics of reduction of AFB(1) to AFB(2) and AFG(1) to AFG(2) by lactic acid has been investigated in dilute aqueous acidic solutions (pH 3.35-4.50) as a function of the concentrations of lactic acid, AFB(1), AFG(1) and hydrogen ion at 37 degrees C. The rate of the reaction was found to be first order with respect to the concentrations of lactic acid and aflatoxins and independent on hydrogen ion concentration. The experimental results are interpreted in terms of mechanisms involving an initial formation of transient oxonium intermediate, which tends to polarize the olefinic (C=C) carbon, which in turn causes the hydride abstraction from alpha-carbon atom of lactic acid in rate determining step. The proposed mechanisms involve an overall transfer of two protons and two electrons from lactic acid to AFB(1) and AFG(1) to give the corresponding reduced less toxic products AFB(2) and AFG(2) and the oxidised product pyruvic acid.

Aflatoxins↗
PubMed2004

Lipase-catalyzed transformation of poly(lactic acid) into cyclic oligomers.

Enzymatic transformations into cyclic oligomers were carried out with the objective of developing chemical recycling of poly(lactic acid)s, such as poly(D,L-lactic acid) (PDLLA), poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA), which are typical biodegradable polymers. They were degraded by lipase in an organic solvent to produce the corresponding cyclic oligomer with a molecular weight of several hundreds. PDLLA (with a Mw of 84,000) was quantitatively transformed into cyclic oligomers by lipase RM (Lipozyme RM IM) in chloroform/hexane at 60 degrees C. PLLA (with a Mw of 120,000) was transformed into cyclic oligomer by lipase CA (Novozym 435) at a higher temperature of 100 degrees C in o-xylene. The oligomer structure was identified by 1H and 13C NMR spectroscopy and MALDI-TOF (matrix assisted laser desorption/ionization-time-of-flight) mass spectrometry.

Biotransformation↗
PubMed1989

Increased peritoneal fluid lactic acid values and progressive bowel strangulation in dogs.

In the present study, we determined values for peritoneal fluid and blood ammonia, amylase, and lactic acid content in 11 dogs after experimental bowel strangulation. In the nine survivors of this group, we demonstrated a near linear increase in peritoneal fluid lactic acid over a 24-hour period, during which the plasma lactic acid remained relatively constant. A significant increase in peritoneal fluid ammonia was also demonstrated, but this did not occur until more than 16 hours after strangulation. In a second group of two dogs in which simple obstruction was produced, no significant increase in peritoneal fluid lactic acid or ammonia occurred. We did not find significant changes in peritoneal fluid amylase in this study. These data suggest that the determination of peritoneal fluid lactic acid content, especially when compared with concomitant plasma lactic acid, may be useful in the accurate preoperative diagnosis of bowel strangulation.

Ammonia↗
PubMed1998

Extracellular dopamine and catabolites in rat striatum during lactic acid perfusion as determined by in vivo microdialysis.

Many experimental studies concerning hypoxia or ischemia have reported a decrease in intra/extracellular pH and massive dopamine (DA) release in the striatum. The present work investigated whether the increase in striatal extracellular DA is related to acidification or to lactate production. Striatal perfusion of lactic acid (pH 5.5) by microdialysis in conscious freely-moving rats induced an increase in extracellular concentrations of DA and catabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), as a probable result of acidification. Perfusion with sodium lactate (pH 7.4) failed to modify DA and catabolite release, whereas orthophosphoric acid produced the same effect as lactic acid. As lactic acidosis is known to induce a displacement of iron from its uptake sites, the possible role of this metal in response to acidosis was studied by perfusing ferrozine, an iron complexing agent, at the same time as lactic acid. The results showed that ferrous ions are involved in the process and suggested that oxygen free radicals play a role in the extracellular release of DA. Thus, lactic acid perfusion in rat striatum would appear to be a useful model for in vivo studies of the mechanisms responsible for increases in extracellular DA during hypoxia and ischemia.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

Freon 11 extraction of volatile metabolites formed by certain lactic Acid bacteria.

The volatile metabolites formed by 18 lactic acid bacteria, representing three genera, were extracted from a complex medium by using a Freon 11 extraction method. The Freon extracts were then analyzed by capillary gas chromatography, and certain extracts were analyzed by gas chromatography-mass spectrometry. A total of 35 major peaks, of which 20 were positively identified, were used to differentiate between the various strains. On the basis of the results obtained, it was possible to differentiate between the members of the genera Lactobacillus, Pediococcus, and Leuconostoc, as well as between various species within the genus Leuconostoc. Of the 10 Leuconostoc oenos strains included in this study, 9 yielded similar results, but it was still possible to differentiate between the various strains. L. oenos B66 differed from the other L. oenos strains. Use of the Freon 11 extraction technique to determine volatile metabolites formed by lactic acid bacteria was shown to be highly reproducible and of great value. Furthermore, certain compounds not previously known to be formed by lactic acid bacteria were found.

Journal Article↗
PubMed2002

Functional and molecular characterisation of lactic acid transport in bovine articular chondrocytes.

Chondrocytes, which control the turnover of cartilage, undergo predominantly glycolytic metabolism due to the avascular nature of the tissue. This will result in high levels of lactic acid production, and this lactic acid must leave the cells for their normal intracellular pH to be maintained. However to date the mechanism by which lactic acid is removed from the chondrocytes has not been elucidated. In the present study lactic acid transport has been characterised using the intracellular pH-sensitive fluorimetric dye BCECF to measure intracellular pH (pH(i)). Addition of extracellular lactic acid-induced an acidification which was sensitive to alpha-cyano-4-hydroxycinnamate (alpha-CHC) and phloretin indicating the involvement of isoform(s) of the monocarboxylate transporter (MCT) family. The results studies of transport kinetics were consistent with the MCT4 isoform (K(m) 14.1mM), common to other glycolytic cells. Western blotting confirmed that MCT4 was the predominantly expressed isoform, although both MCT1 and MCT4 transcripts were present when cells were assayed by RT-PCR. Through effects on pH(i), the activity of this transporter may therefore modify cartilage turnover.

Animals↗
PubMed2002

Coupled lactic acid fermentation and adsorption.

Polyvinylpyridine (PVP) and activated carbon were evaluated for coupled lactic acid fermentation and adsorption, to prevent the product concentration from reaching inhibitory levels. The lactic acid production doubled as a result of periodical circulation of the fermentation broth through a PVP adsorption column. The adsorbent was then regenerated and the adsorbed lactate harvested, by passing 0.1 N NaOH through the column. However, each adsorption-regeneration cycle caused about 14% loss of the adsorption capacity, thus limiting the practical use of this rather expensive adsorbent. Activated carbon was found much more effective than PVP in lactic acid and lactate adsorption. The cells of Lactobacillus delbrueckii subsp. delbrueckii (LDD) also had strong tendency to adsorb on the carbon. A study was therefore conducted using an activated carbon column for simultaneous cell immobilization and lactate adsorption, in a semi-batch process with periodical medium replacement. The process produced lactate steadily at about 1.3 g l(-1)h(-1) when the replacement medium contained at least 2 g l(-1) of yeast extract. The production, however, stopped after switching to a medium without yeast extract. Active lactic acid production by LDD appeared to require yeast extract above a certain critical level (<2 g l(-1)).

Adsorption↗
PubMed2005

Tissue restoration after resorption of polyglycolide and poly-laevo-lactic acid screws.

Despite worldwide clinical use of bio-absorbable devices for internal fixation in orthopaedic surgery, the degradation behaviour and tissue replacement of these implants are not fully understood. In a long-term experimental study, we have determined the patterns of tissue restoration 36 and 54 months after implantation of polyglycolic acid and poly-laevo-lactic acid screws in the distal femur of the rabbit. After 36 months in the polyglycolic acid group the specimens showed no remaining polymer and loose connective tissue occupied 80% of the screw track. Tissue restoration remained poor at 54 months, the amounts of trabecular bone and haematopoietic elements being significantly lower than those in the intact control group. The amount of trabecular bone within the screw track at 54 months in the polyglycolic acid group was less than in the empty drill holes (p = 0.04). In the poly-laevo-lactic acid group, polymeric material was present in abundance after 54 months, occupying 60% of the cross-section of the core area of the screw track. When using absorbable internal fixation implants we should recognise that the degradation of the devices will probably not be accompanied by the restoration of normal trabecular bone.

Absorbable Implants↗
PubMed1993

[Hemodynamic effects of dobutamine in critical patients: discrepancies between parameters of tissue oxygenation and lactic acid].

A retrospective study on the effects of dobutamine on hemodynamic parameters of tissue oxygenation and lactic acid levels was performed in 35 patients. The use of the drug in a mean dose of 5.0 +/- 2.1 ug/kg/min was associated with a significant increase in cardiac index, oxygen transport and consumption and decrease in arterial lactic acid levels. A separate analysis of patients with or without basal hyperlactacidemia and those with favorable (decrease) or unfavorable (no change or increase) lactic acid response to the drug, was performed. This analysis disclosed important disagreements between changes in hemodynamic parameters of oxygen consumption and transport and arterial lactic acid levels, as indexes of tissue perfusion. It is concluded that is advisable to monitor together hemodynamics, oxygen transport and consumption and arterial lactic acid in patients with severe cardiorespiratory disturbances or shock.

Adult↗
PubMed1994

Synovial-fluid D-lactic acid in bacterial and other acute joint effusions.

The use of D-lactic acid in differential diagnosis of bacterial arthritis was evaluated in a prospective study. The concentration of D-lactic acid was determined by the enzymatic UV-method in sixty-eight synovial fluids (SF) and in twenty four sera from adult patients with acute knee effusion. High concentrations of D-lactic acid (> 0.15 mmol/l) were measured most frequently in SF from bacterial arthritis, but also in individual culture-negative SF samples from patients with inflammatory culture-negative joint effusions with and without identified history of infections. Determination of SF D-lactic acid is not useful in differential diagnosis of bacterial arthritis.

Arthritis, Infectious↗
PubMed2000

Class II antimicrobial peptides from lactic acid bacteria.

Strains of lactic acid bacteria (LAB) produce a wide variety of antibacterial peptides. More than fifty of these so-called peptide bacteriocins have been isolated in the last few years. They contain 20-60 amino acids, and are cationic and hydrophobic in nature. Several of these bacteriocins consist of two complementary peptides. The peptide bacteriocins of LAB are inhibitory at concentrations in the nanomolar range, and cause membrane permeabilization and leakage of intracellular components in sensitive cells. The inhibitory spectrum is limited to gram-positive bacteria, and in many cases to bacteria closely related to the producing strain. Among the target organisms are food spoilage bacteria and pathogens such as Listeria, so that many of these antimicrobial peptides could have a potential as food preservatives as well as in medical applications.

Amino Acid Sequence↗
PubMed1983

Carbohydrate metabolism in lactic acid bacteria.

The term "lactic acid bacteria" is discussed. An overview of the following topics is given: main pathways of homo- and heterofermentation of hexoses, i.e. glycolysis, bifidus pathway, 6-phosphogluconate pathway; uptake and dissimilation of lactose (tagatose pathway); fermentation of pentoses and pentitols; alternative fates of pyruvate, i.e. splitting to formate and acetate, CO2 and acetate or formation of acetoin and diacetyl; lactate oxidation; biochemical basis for the formation of different stereoisomers of lactate.

Actinomycetaceae↗
PubMed2004

Enhancement in ex vivo phagocytic capacity of peritoneal leukocytes in mice by oral delivery of various lactic-acid-producing bacteria.

Lactic-acid-producing bacteria (LABs) are known to have immunomodulating activity. In the current study, various LABs were tested for their immunity-enhancing activity, especially the phagocytic activity of leukocytes. Viable but not heat-killed cells of Weissella kimchii strain PL9001, Lactobacillus fermentum strain PL9005, and L. plantarum strain PL9011 significantly increased the ex vivo phagocytic capacity of mouse peritoneal leukocytes to ingest fluorescein isothiocyanate (FITC)-labeled Escherichia coli in a strain-dependent manner. Results of this and previous studies suggest these LABs as candidates for new probiotics. This is the first report of the enhancement of peritoneal leukocyte activity of these species.

Adjuvants, Immunologic↗
PubMed1995

Taxonomy of lactic acid bacteria associated with vacuum-packaged processed meat spoilage by multivariate analysis of cellular fatty acids.

The taxonomy of lactic acid bacteria from vacuum-packaged processed meats is problematic, and atypical members of the leuconostocs and the Lactobacillus sake / curvatus group are often encountered. In order to resolve this problem the cellular fatty acid (CFA) content of 61 isolates from vacuum-packaged vienna sausages and 18 reference strains was determined by gas chromatography. The relationship between strains was derived by principal component analysis of data. The CFA profiles were highly reproducible. Although no relationships could be derived using only one or two differentiating CFAs, plots of the first two principal components based on only the six most variable CFAs allowed grouping of strains. The two genera (Leuconostoc and Lactobacillus) could not be clearly separated when analysed together, but differentiation of species within each of the genera was achieved when they were analysed independently. Examination of plots for the reference strains confirmed previously established relationships between these strains. From the plot of the Lactobacillus sake / Lactobacillus curvatus component of the study it was found that most atypical Lactobacillus sake / curvatus strains were closely related to the typical Lactobacillus sake isolates and reference strain, while the Lactobacillus curvatus strains formed an independent grouping. A small cluster of atypical strains, however, indicated that this relationship may not be true for all these strains. Among the leuconostocs only isolates of Leuconostoc mesenteroides could be clearly differentiated.

Fatty Acids↗
PubMed2005

Inhibition of allergen-induced airway inflammation and hyperreactivity by recombinant lactic-acid bacteria.

Recombinant lactic-acid bacteria (LAB) are able to inhibit allergen-specific T-cell responses. In this study, we examined whether oral feeding of recombinant LAB was able to suppress allergen-induced airway inflammation and hyperreactivity (AHR) in a murine model. Animals were intraperitoneally sensitized with Dermatophagoides pteronyssinus group-5 allergen (Der p 5) and orally treated with recombinant LAB containing a plasmid-encoded Der p 5 gene or placebo on day 7 and day 14 for three days consecutively. Twenty-one days after sensitization, mice underwent inhalational challenging. Der p 5-specific immunological responses including changes to specific immunoglobulin G and E (IgE) levels, the presence of cells in the bronchoalveolar lavage fluid (BALF), and AHR were assessed following this inhalational challenge. We demonstrated that oral feeding of recombinant LAB could significantly decrease the synthesis of Der p 5-specific IgE, and AHR. Furthermore, following such treatment, we also noted that both neutrophils and eosinophils had infiltrated the BALF to a significantly lower extent, when compared to the vehicle-treated group. Neither recombinant allergen nor LAB alone was able to suppress allergen-induced immune responses. Our findings suggest that treatment with recombinant LAB at a low dose can suppress allergen-induced airway allergic inflammation, this providing a basis for developing a novel therapeutic method for allergic airway diseases.

Administration, Oral↗
PubMed2001

Determination of peroxy radical-scavenging of lactic acid bacteria.

Responses of lactic acid bacteria (LAB) to peroxy radicals generated via thermal (40 degrees C) decomposition of the diazocompound 2,2,-azo-bis (2-amidinopropane) dihydrochloride (ABAP), were studied. In general, LAB displayed survival curves with shoulders and tails indicative of 'multihit' killing by exposure to peroxy radicals. One strain, Lactococcus lactis subsp. lactis DIP15, producing a slope of 0.0105 in the kinetic analysis when exposed to 4 mM ABAP, exhibited a measurable antioxidant capacity. The other LAB failed to show any significant antioxidant capacity. The antioxidant capacity of strain DIP15 remained constant after cells have been heat-treated, suggesting that compounds bearing free radical scavenging capacity are rather stable.

Amidines↗