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PubMed2000

Metabolic engineering of Lactobacillus helveticus CNRZ32 for production of pure L-(+)-lactic acid.

Expression of D-(-)-lactate dehydrogenase (D-LDH) and L-(+)-LDH genes (ldhD and ldhL, respectively) and production of D-(-)- and L-(+)-lactic acid were studied in Lactobacillus helveticus CNRZ32. In order to develop a host for production of pure L-(+)-isomer of lactic acid, two ldhD-negative L. helveticus CNRZ32 strains were constructed using gene replacement. One of the strains was constructed by deleting the promoter region of the ldhD gene, and the other was constructed by replacing the structural gene of ldhD with an additional copy of the structural gene (ldhL) of L-LDH of the same species. The resulting strains were designated GRL86 and GRL89, respectively. In strain GRL89, the second copy of the ldhL structural gene was expressed under the ldhD promoter. The two D-LDH-negative strains produced only L-(+)-lactic acid in an amount equal to the total lactate produced by the wild type. The maximum L-LDH activity was found to be 53 and 93% higher in GRL86 and GRL89, respectively, than in the wild-type strain. Furthermore, process variables for L-(+)-lactic acid production by GRL89 were optimized using statistical experimental design and response surface methodology. The temperature and pH optima were 41 degrees C and pH 5.9. At low pH, when the growth and lactic acid production are uncoupled, strain GRL89 produced approximately 20% more lactic acid than GRL86.

Bioreactors↗
PubMed2000

Molecular diversity of lactic acid bacteria from cassava sour starch (Colombia).

Lactic acid bacteria and more particularly lactobacilli and Leuconostoc, are widely found in a wide variety of traditional fermented foods of tropical countries, made with cereals, tubers, meat or fish. These products represent a source of bacterial diversity that cannot be accurately analysed using classical phenotypic and biochemical tests. In the present work, the identification and the molecular diversity of lactic acid bacteria isolated from cassava sour starch fermentation were assessed by using a combination of complementary molecular methods: Randomly Amplified Polymorphic DNA fingerprinting (RAPD), plasmid profiling, hybridization using rRNA phylogenetic probes and partial 16S rDNA sequencing. The results revealed a large diversity of bacterial species (Lb. manihotivorans, Lb. plantarum, Lb. casei, Lb. hilgardii, Lb. buchneri, Lb. fermentum, Ln. mesenteroides and Pediococcus sp.). However, the most frequently isolated species were Lb. plantarum and Lb. manihotivorans. The RAPD analysis revealed a large molecular diversity between Lb. manihotivorans or Lb. plantarum strains. These results, observed on a rather limited number of samples, reveal that significant bacterial diversity is generated in traditional cassava sour starch fermentations. We propose that the presence of the amylolytic Lb. manihotivorans strains could have a role in sour starch processing.

DNA, Ribosomal↗
PubMedDate not supplied

Polydepsipeptides. 5. Experimental conformational analysis of poly(L-alanyl-L-lactic acid) and related model compounds.

In this paper we report an experimental conformational analysis of the depsipeptide model compounds acetyl-L-alanine methyl ester, acetyl-L-lactic acid N-methylamide, and acetyl-L-alanyl-L-lactic acid N-methylamide and of the sequential polydepsipeptide poly(L-alanyl-L-lactic acid). The model depsipeptides were examined in dilute organic solutions by infrared and nuclear magnetic resonance spectroscopy. Neither acetyl-L-alanine methyl ester nor acetyl-L-lactic acid N-methylamide assumes an intramolecularly hydrogen-bonded conformation. Acetyl-L-alanyl-L-lactic acid N-methylamide, on the other hand, in dilute chloroform or dilute carbon tetrachloride solutions, strongly favors a conformation with an intramolecular hydrogen bond between the N-H hydrogen atom of its N-methylamide group and the carbonyl oxygen atom of its acetyl group. Comparison of theoretical and experimental circular dichroism suggests that poly(L-alanyl-L-lactic acid) is partially ordered in chloroform solution with approximately 50% of its repeat units in the R10 helix, an ordered conformation found by our previous theoretical analysis to have a low intramolecular conformational energy.

Alanine↗
PubMed1997

Immune modulation of blood leukocytes in humans by lactic acid bacteria: criteria for strain selection.

Lactic acid bacteria in food can transiently colonize the intestine and exert beneficial effects (probiotic). Survival during intestinal transit or adhesion to epithelium or both seem to be important for modifying the host's immune reactivity. Because Lactobacillus acidophilus strain La1 is adherent to enterocytes in vitro, we hypothesize that contact with immune cells may occur in vivo. However, Bifidobacterium bifidum strain Bb12, which shows high fecal colonization, is another potential immunomodulator. Twenty-eight volunteers were divided into two groups and given a fermented product containing one of the two strains. Lymphocyte subsets and leukocyte phagocytic activity were studied in blood. No modifications were detected in lymphocyte subsets. In contrast, phagocytosis of Escherichia coli ssp. was enhanced in both groups (P < 0.001 for both). Bacterial adhesion to enterocytes, fecal colonization, or both seem to be valuable selection criteria for immunomodulation. Antiinfective mechanisms of defense can be enhanced after ingestion of specific lactic acid bacteria strains.

Adult↗
PubMedDate not supplied

Mathematical model for analysis of mass transfer for immobilized cells in lactic acid fermentation.

A new mathematical model is proposed to analyze the mass transfer behavior in lactic acid fermentation using immobilized cells entrapped in calcium alginate. The model is comprised of material balance equations for glucose, free lactic acid, and several ions. The dissociation rate of lactic acid (rdiss) is involved in the proposed equations. To solve the equations numerically, a modified calculating method is proposed. Through model analysis, the possible mass transfer behavior in the gel bead was discussed. The model is validated by comparisons with the experimental results obtained from batch and continuous fermentation. The simulations using the model were made to investigate the mass transfer limitation in the gel beads. The results showed that the cell density gradient was formed in the gel beads and it was caused by the accumulation of the inhibitory product (free lactic acid), not by substrate starvation. Moreover, unusual mass transfer behavior of lactate ion in the immobilization support was pointed out.

Biotechnology↗
PubMed1982

Inhibition of hexokinase and protein kinase activities of tumor cells by a chloromethyl ketone derivative of lactic acid.

A chloromethyl ketone derivative of lactic acid is a potent inhibitor of glycolysis of Ehrlich ascites tumor cells. It inhibited glycolysis of intact cells by about 50% at 200 microM (100 nmol/mg of protein) while cell-free extracts were inhibited 50% at 50 microM (50 nmol/mg of protein). N alpha-(p-Tosyl)-L-lysine chloromethyl ketone and N alpha-(p-tosyl)-L-phenylalanine chloromethyl ketone inhibited only slightly or not at all at this concentration. The inhibition was localized at the hexokinase and phosphofructokinase steps since these two enzymes added to an inactivated extract restored the glycolytic activity, whereas none of the other glycolytic enzymes did. In fact, addition of pyruvate kinase or lactate dehydrogenase, which stimulated glycolysis, resulted in a more pronounced inhibition. Glycolysis and hexokinase activities in extracts of Rous sarcoma virus transformed cells were considerably more sensitive to the inhibitor than the activities from normal chick embryo fibroblasts. Hexokinase from mouse brain required 50 times higher concentrations for inhibition than the enzyme from mouse Ehrlich ascites tumor cells. Yeast hexokinase was unaffected at all concentrations tested. Since 5,5'-dithiobis(2-nitrobenzoate) protected against the inhibition, the chloromethyl ketone appeared to inhibit by interaction with an essential SH group. A pronounced inhibition of protein kinase activity of plasma membranes of Ehrlich ascites tumor cells was observed in the presence of the chloromethyl ketone. As in the case of glycolysis, the chloromethyl ketone of lactic acid was a more potent inhibitor of protein kinase activity than several other chloromethyl ketones that were tested.

Animals↗
PubMed2006

Statistical screening of medium components by Plackett-Burman design for lactic acid production by Lactobacillus sp. KCP01 using date juice.

Statistical screening of media components for production of lactic acid by Lactobacillus sp. KCP01 using date juice as a sugar source was carried out by Plackett-Burman design. Date juice at 5% sugar concentration when used alone showed 2.6 g/l of lactic acid production. Increase in lactic acid production (15.1 g/l) was observed with supplementation of salts and organic nitrogen sources of MRS medium and after optimization of pH and temperature using date juice as a C-source. Plackett-Burman design showed peptone, K2HPO4, sodium acetate and date juice as significant components influencing the lactic acid production.

Arecaceae↗
PubMed1996

Effect of monolaurin and lactic acid on Listeria monocytogenes attached to catfish fillets.

The purpose of this study was to determine the effects of monolaurin and lactic acid, singly or combined, on Listeria monocytogenes attached to catfish fillets. Skinless catfish fillets were inoculated with L. monocytogenes and dip treated in monolaurin and/or lactic acid solution for various time periods. Results showed that monolaurin up to 400 micrograms/ml had no influence on counts. Conversely, lactic acid-treated fillets had reduced counts compared to controls. Dipping in 0.85, 1.70, or 2.55% lactic acid for 30 min reduced counts by 0.9, 1.4, or 1.3 logs, respectively. Extending the dipping time to 60 min resulted in little additional decrease in counts. Combining monolaurin with lactic acid yielded results similar to lactic acid alone. Hence, population reduction ability resides with lactic acid and not monolaurin.

Animals↗
PubMed2006

Modelling Yersinia enterocolitica inactivation in coculture experiments with Lactobacillus sakei as based on pH and lactic acid profiles.

In food processing and preservation technology, models describing microbial proliferation in food products are a helpful tool to predict the microbial food safety and shelf life. In general, the available models consider microorganisms in pure culture. Thus, microbial interactions are ignored, which may lead to a discrepancy between model predictions and the actual microbial evolution, particularly for fermented and minimally processed food products in which a background flora is often present. In this study, the lactic acid mediated negative microbial interaction between the lactic acid bacterium Lactobacillus sakei and the psychrotrophic food pathogen Yersinia enterocolitica was examined. A model describing the lactic acid induced inhibition (i.e., early induction of the stationary phase) of the pathogen [Vereecken, K.M., Devlieghere, F., Bockstaele, A., Debevere, J., Van Impe, J.F., 2003. A model for lactic acid induced inhibition of Yersinia enterocolitica in mono- and coculture with Lactobacillus sakei. Food Microbiology 20, 701-713.] was extended to describe the subsequent inactivation (i.e., decrease of the cell concentration to values below the detection limit). In the development of a suitable model structure to describe the inactivation process, critical points in the variation of the specific evolution rate mu [1/h] with the dynamic (time-varying) pH and undissociated lactic acid profiles were taken into account. Thus, biological knowledge, namely, both pH and undissociated lactic acid have an influence on the microbial evolution, was incorporated. The extended model was carefully validated on new data. As a result, the newly developed model is able to accurately predict the growth, inhibition and subsequent inactivation of Y. enterocolitica in coculture as based on the dynamic pH and lactic acid profiles of the medium.

Antibiosis↗
PubMed2006

Production of lactic acid from cheese whey by batch and repeated batch cultures of Lactobacillus sp. RKY2.

The fermentative production of lactic acid from cheese whey and corn steep liquor (CSL) as cheap raw materials was investigated by using Lactobacillus sp. RKY2 in order to develop a cost-effective fermentation medium. Lactic acid yields based on consumed lactose were obtained at more than 0.98 g/g from the medium containing whey lactose. Lactic acid productivities and yields obtained from whey lactose medium were slightly higher than those obtained from pure lactose medium. The lactic acid productivity gradually decreased with increase in substrate concentration owing to substrate and product inhibitions. The fermentation efficiencies were improved by the addition of more CSL to the medium. Moreover, through the cell-recycle repeated batch fermentation, lactic acid productivity was maximized to 6.34 g/L/h, which was 6.2 times higher than that of the batch fermentation.

Bioreactors↗
PubMed1970

Bacteriophage active against the lactic acid beverage-producing bacterium Lactobacillus casei.

A virulent bacteriophage which causes a decrease in acid production during fermentation of a lactic acid beverage named Yakult with Lactobacillus casei was isolated from the abnormal fermentation tank and named PL-1. L. casei S strain was the exclusive host cell among 18 lactic acid bacteria tested. The plaque was round with an average diameter of about 0.5 mm. It exhibited serological cross-reaction with previously isolated J1 phage. Under an electron microscope, the phage had a spermatozoon shape, with an icosahedral head (63 nm) and a long tail (12.5 by 275 nm) with about 55 striae. The free phage particles were stable at pH 5 to 8. The phage was quite sensitive to ultraviolet irradiation or to heating (60 C, 5 min), and the host was more sensitive than the phage to these treatments. Many kinds of antimicrobial chemicals were also phagocidal. Calcium ion (5 mm) was specifically essential for the phage growth cycle. A one-step growth experiment under optimum conditions (37 C and pH 6.0) showed that the eclipse period was about 75 min, that the latent period was 100 min after the phage infection, and that the average burst size was about 200. The possibility of arresting phage development in lactic acid fermentation is discussed.

Animals↗
PubMed1985

Effect of anti-oxidants on growth and lactic acid production by Streptococcus mutans.

The effects of three anti-oxidants--tertiary butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT)--on both growth and lactic acid production by eight cariogenic strains of Streptococcus mutans were investigated. Synergistic inhibitory effects of potassium sorbate on lactic acid production were also determined. All three anti-oxidants are phenolic derivatives and are commonly used in food systems due to their excellent "carry-through" properties during processing. Growth inhibition was determined by turbidity measurements at 600 nm. Lactic acid was assayed by gas chromatography, and bacterial DNA was assayed by the diphenylamine reaction. There were reduced growth levels of S. mutans due to the anti-oxidants and potassium sorbate for at least 12 hr, with TBHQ and BHA still inhibiting growth at 24 hr. Nearly all concentrations of anti-oxidants and potassium sorbate reduced lactic acid production by S. mutans, but only TBHQ significantly inhibited lactic acid production when the amount of acid per microgram DNA was calculated. A synergistic reduction of lactic acid production by S. mutans does occur in most combinations of potassium sorbate with anti-oxidants.

Anisoles↗
PubMed2004

Polymer alloys of Nodax copolymers and poly(lactic acid).

Properties of polymer alloys comprising poly(lactic acid) and Nodax copolymers are investigated. Nodax is a family of bacterially produced polyhydroxyalkanoate (PHA) copolymers comprising 3-hydroxybutyrate (3HB) and other 3-hydroxyalkanoate (3HA) units with side groups greater than or equal to three carbon units. The incorporation of 3HA units with medium-chain-length (mcl) side groups effectively lowers the crystallinity and the melt temperature, Tm, of this class of PHA copolymers, in a manner similar to that of alpha olefins controlling the properties of linear low density polyethylene. The lower Tm makes the material easier to process, as the thermal decomposition temperature of PHAs is then relatively low. The reduced crystallinity provides the ductility and toughness required for many plastics applications. When a small amount of ductile PHA is blended with poly(lactic acid) (PLA), a new type of polymer alloy with much improved properties is created. The toughness of PLA is substantially increased without a reduction in the optical clarity of the blend. The synergy between the two materials, both produced from renewable resources, is attributed to the retardation of crystallization of PHA copolymers finely dispersed in a PLA matrix as discrete domains.

Biopolymers↗
PubMed1994

The immediate bactericidal effect of lactic acid on meat-borne pathogens.

The kinetics of the bactericidal effect of lactic acid decontamination (LAD) on meat-borne pathogens (Salmonella spp., Campylobacter jejuni and Listeria monocytogenes) was studied in an in-vitro model. The bactericidal effect was greatest on organisms in the lactic acid film that replaced the natural fluid on the meat surface during LAD. A stepwise increase in pH from 2.6 to 3.5 and 4.0 progressively reduced the bactericidal effect of decontamination. For treatment with 2% lactic acid for 30-90 s at 21 degrees C, the immediate death of Salmonella spp. decreased from about 0.5-2 log10 cfu at pH 2.6 to an insignificant level at pH 4.0. The immediate death for Camp. jejuni decreased from 2.6 to > 5.3 at pH 2.6 to 0.3-1.0 at pH 4.0. The decrease in bactericidal effect with increasing pH could, however, be countered by an increase in the temperature from 21 degrees C to 37 degrees C. It is suggested that 2% LAD at 37 degrees C for 30-90 s is suitable for elimination of salmonellas on meat but not for L. monocytogenes. Decontamination with 1% lactic acid at pH 3.0 and 21 degrees C for at least 30 s was effective for Camp. jejuni. Mesophilic Enterobacteriaceae were reliable indicators of the LAD-induced bactericidal effect on Salmonella spp. and Camp. jejuni.

Buffers↗
PubMed2001

Biodegradable hydrogels based on stereocomplex formation between lactic acid oligomers grafted to dextran.

A novel hydrogel system in which crosslinking is established by stereocomplex formation between lactic acid oligomers of opposite chirality is proposed. To investigate the feasibility of this novel system, we first investigate whether there is an operation window where lactic acid oligomers in either the D- or L-form do not give a crystalline phase, whereas in a blend of the D- and L-form stereocomplex formation occurs. Therefore, D- and L-lactic acid oligomers with different degrees of polymerization (DP) were prepared and analyzed using DSC. It was shown that crystallinity was present in D- or L-oligomers with DP > or = 11. On the other hand, in blends of D- and L-oligomers of lactic acid crystallinity (stereocomplexation) was already observed at a DP > or = 7. In the next step, L- and D-lactic acid oligomers were coupled via their terminal hydroxyl group to dextran, yielding dex-(L)lactate and dex-(D)lactate, respectively. Upon dissolving each product in water separately and mixing the solutions, a hydrogel is formed at room temperature as demonstrated by rheological measurements. The storage modulus of the obtained hydrogel strongly decreased upon heating to 80 degrees C, while it was restored upon cooling to 20 degrees C demonstrating the thermo-reversibility and the physical nature of the cross-links. The storage modulus of the gels depends on the degree of polymerization of the lactate acid grafts and their degree of substitution on dextran. Interestingly, gel formation was favored when one lactic oligomer was coupled via its hydroxyl group whereas the oligomer of opposite chirality was coupled via its carboxylic acid group. This is ascribed to the parallel packing of the oligomers in stereocomplexes.

Calorimetry, Differential Scanning↗
PubMed1991

The concentration of lactic acid in breast milk following maximal exercise.

The purpose of this study was to investigate the concentration of lactic acid in breast milk following maximal exercise. Seven active postpartum women (2 to 24 months) were exercised to maximum on a treadmill (VO2 max = 37.0 +/- 13.7 ml.min-1.kg-1). Blood was sampled via finger prick at rest before exercise and 5 minutes postexercise; milk was collected via self expression at rest before exercise and at 10 and 30 minutes postexercise. Both blood and milk were analyzed for lactic acid via enzymatic methods. Following maximal exercise, a significant increase in the concentration of lactic acid was found in the blood at 5 minutes postexercise and breast milk at 10 minutes postexercise. Although elevated, the lactic acid concentration of the 30-minute sample of breast milk was not significantly different from the resting sample. Maximal exercise can result in significant increase in lactic acid concentration in breast milk. Further research is needed to demonstrate whether the taste of the milk is affected.

Breast Feeding↗
PubMed1975

[Changes in blood pressure and impulse activity in intestinal nerves during exposure of small intestine interoreceptors to lactic acid].

I. a. administration of threshold concentration (0.2 ml 7.8 mM) of lactic acid into the small intestine was found to increase afferent and efferent impulsation in the intestinal nerves as well as the systemic arterial blood pressure in anesthetized cats. Increase in the lactic acid concentration up to 250 mM/l resulted in two-phasic augmentation of the nerve responses and of the pressor reflexes. In the range from 7.8 to 62.5 mM/l of lactic acid concentration the absolute magnitude of pressor reflexes was 2.3 +/- 0.6--4.2 +/- 0.5 mm Hg. Further increase in the lactic acid concentration (up to 250 mM/l) produced on augmentation in the reflexes magnitude up to 18 +/- 2.8 mm Hg. A possible functional role of afferent impulses generated by the tissue receptors following an increase in metabolites concentration in the organs, is discussed.

Animals↗
PubMedDate not supplied

[Health effects of lactic acid bacteria ingested in fermented milk].

Health effects of lactic acid bacteria ingested in fermented milk. Many recent studies have shown the health effects of various strains of lactic acid bacteria in humans and animals and have tried to describe their action mechanism in the digestive tract. A number and a variety of potential beneficial effects have been published. Some of these effects have already been described such as the improvement of lactose digestion and the treatment of diarrheal disorders. Other health effects are still a subject of controversy such as the decrease of serum cholesterol and the reduction of tumor formation. The aim of this article is to summarize the probiotic effects of lactic acid bacteria, their mechanisms, and the fate of these microorganisms during their transit in the digestive tract.

Animals↗