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PubMed2006

Use of inexpensive nitrogen sources and starch for L(+) lactic acid production in anaerobic submerged fermentation.

L(+) Lactic acid fermentation was studied by Lactobacillus amylophilus GV6 under the influence of inexpensive nitrogen sources (red lentil-RL, and Baker's yeast cells-YC) and starch by response surface methodology (RSM). Central composite rotatable design (CCRD) was employed to determine maximum lactic acid production at optimum values for process variables RL, YC and incubation period (IP) and a satisfactory fit model was realized. Lactic acid production was significantly affected by RL and IP interactions as well as by independent variables RL and YC. Maximum lactic acid production of 13.5 g/15.2g starch was obtained with RL 0.8%, YC 1% and IP of 48 h, with 92% lactic acid yield efficiency (g lactic acid produced/g substrate utilized) and 40% increase (from 50 g to 92 g/100 g starch utilized) in lactic acid production. This is the first report on response optimization in direct fermentation of starch to lactic acid using inexpensive nitrogen sources substituting peptone and yeast extract in anaerobic submerged fermentation by amylolytic lactic acid bacteria (LAB).

Anaerobiosis↗
PubMed2004

Release kinetics of hydrophobic and hydrophilic model drugs from pluronic F127/poly(lactic acid) nanoparticles.

Poly(lactic acid) (PLA) was successfully grafted to both ends of Pluronic F127 block copolymers (PEO-PPO-PEO) to obtain amphiphilic PLA-F127-PLA block copolymers. The block composition and structure of PLA-F127-PLA block copolymers were studied by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetric (DSC) and wide angle X-ray diffraction (WXRD) techniques. Data from DSC and WXRD measurements indicated that Tg and Tm of PLA blocks in PLA-F127-PLA block polymers are lower than those of PLA homopolymer. Furthermore, Tm and crystallinity of PLA blocks decrease with decreasing PLA block length in PLA-F127-PLA block copolymers. The release behaviors of both hydrophobic 9-(methylaminomethyl)anthracene (MAMA) and hydrophilic procaine hydrochloride (PrHy) model drugs from PLA-F127-PLA nanoparticles with vesicular structure in PBS solution at 37 degrees C were examined by UV spectroscopy. The release kinetics of both MAMA and PrHy model drugs from PLA-F127-PLA nanoparticles exhibit burst release characteristics, which are believed to be controlled by concentration gradient resulting from the slow hydrolytic degradation of PLA segments.

Hydrophobic and Hydrophilic Interactions↗
PubMedDate not supplied

Preparation and properties of plasticized poly(lactic acid) films.

Poly(lactic acid), PLA, was blended with monomeric and oligomeric plasticizers in order to enhance its flexibility and thereby overcome its inherent problem of brittleness. Differential scanning calorimetry, dynamic mechanical analysis, transmission electron microscopy, and tensile testing were used to investigate the properties of the blends. Monomeric plasticizers, such as tributyl citrate, TbC, and diethyl bishydroxymethyl malonate, DBM, drastically decreased the T(g) of PLA, but the blends showed no morphological stability over time since rapid cold crystallization caused a size reduction of the amorphous domains in PLA. Consequently, the ability of PLA to accommodate the plasticizer diminished with the increase in crystallinity and migration of the plasticizer occurred. Increasing the molecular weight of the plasticizers by synthesizing oligoesters and oligoesteramides resulted in blends that displayed T(g) depressions slightly smaller than with the monomeric plasticizers. The compatibility with PLA was dependent on the molecular weight of the oligomers and on the presence or not of polar amide groups that were able to positively interact with the PLA chains. Aging the materials at ambient temperature revealed that the enhanced flexibility as well as the morphological stability of the films plasticized with the oligomers could be maintained as a result of the higher molecular weight and the polar interactions with PLA.

Lactic Acid↗
PubMed2004

Bioconversion of waste office paper to L(+)-lactic acid by the filamentous fungus Rhizopus oryzae.

L(+)-lactic acid production was investigated using an enzymatic hydrolysate of waste office automation (OA) paper in a culture of the filamentous fungus Rhizopus oryzae. In 4 d culture, 82.8 g/l glucose, 7 g/l xylose, and 3.4 g/l cellobiose contained in the hydrolysate were consumed to produce 49.1 g/l of lactic acid. The lactic acid yield and production rate were only 0.59 g/g and 16.3 g/l/d, respectively, only 75% and 61% of the results from the glucose medium. The low production rate from waste OA hydrolysate was elucidated by trials using xylose as the sole carbon source; in those trials, the lactic acid production rate was 7.3 g/l/d, only 28% that of glucose or cellobiose. The low lactic acid yield from waste OA hydrolysate was clarified by trials using artificial hydrolysates comprised of 7:2:1 or 7:1:2 ratios of glucose:cellobiose:xylose. For both, the lactic acid production rate of 17.4 g/l/d matched that of waste OA paper, while the lactic acid yield was similar to that of the glucose medium. This indicates that the production rate may be inhibited by xylose derived from hemicellulose, and the yield may be inhibited by unknown compounds derived from paper pulp.

Acremonium↗
PubMed1983

Diagnostic use of cerebrospinal fluid lactic acid levels in meningitis.

Analysis of cerebrospinal fluid lactic acid levels in 62 patients suspected of having meningitis was performed. Lactic acid was measured enzymatically using lactic acid dehydrogenase with the liberation of NADH. In a control (no meningitis) group, 46 children had a mean cerebrospinal fluid lactic acid level of 14.7 +/- 2.2 mg/dl; 3 with febrile seizure had a mean lactic acid level of 33.5 +/- 0.98 mg/dl. In 9 cases of bacterial meningitis, the mean lactic acid level was 54.8 +/- 16.8 mg/dl. In 3 patients of aseptic meningitis, the mean lactic acid level was 34.5 +/- 1.0 mg/dl. Serial lactate determination was done in three patients and they were well correlated with the clinical response and other cerebrospinal fluid findings. These data suggest that the determination of cerebrospinal fluid lactic acid may be of diagnostic value in differentiating between bacterial and aseptic meningitis.

Adolescent↗
PubMedDate not supplied

An empirical model on extractive lactic acid bioconversion.

The commercial production of lactic acid through fermentation process has always been in competition with its chemical synthesis process (Kirk Othmer, 1995). Lactic acid produced through the fermentation process has to cope with the problems of purification to meet the required quality standards. An attempt to improve the fermentative production is possible by proper design of an industrial process involving low capital cost for the plant. Also, the low energy costs both in its fermentation and purification, are required. In the commercial interest, the investment cost should be minimised, which is possible only when the cell density in fermenter is high. It means that the inhibitory effect of the product on process kinetics must be minimised. Based on these requirements, the extractive bioconversion technique is one of the approaches to achieve the commercially viable lactic acid production. Extractive lactic acid bioconversion using ion-exchange resin process has already been described in our earlier publications (Srivastava e al., 1992: Roychoudhury et al., 1995) It is always an advantage to develop a process model, thus opening an area of biotechnological improvements to the process. In the present paper, an empirical mathematical model has been described to explain this extractive bioconversion using ion-exchange resin process. It was based on generalised Monod's growth model and Leudeking and Piret equation. The system was defined with the assumption that the microbial growth can be represented as a single reaction; only a very little part of the substrate is utilised for the maintenance of the cells. The effect of end product inhibition on growth and product formation kinetics has also been considered in this model. A non-linear regression technique was used for evaluation of bioconversion kinetic parameters. The fourth order Runge Kutta method was used for solving the differential equations. The results of this process simulation are also discussed in the present paper. It indicates that the use of present technique has minimised the effect of lactic acid inhibition on process kinetics and hence higher productivity and least substrate utilisation for maintenance of cells. A statistical F-test has been performed for determining the validity of the model for a given set of experimental data with a level of significance alpha = 0.05 selected for this extractive batch recycle bioconversion process using ion-exchange resin.

Adsorption↗
PubMed2002

Influence of medium buffering capacity on inhibition of Saccharomyces cerevisiae growth by acetic and lactic acids.

Acetic acid (167 mM) and lactic acid (548 mM) completely inhibited growth of Saccharomyces cerevisiae both in minimal medium and in media which contained supplements, such as yeast extract, corn steep powder, or a mixture of amino acids. However, the yeast grew when the pH of the medium containing acetic acid or lactic acid was adjusted to 4.5, even though the medium still contained the undissociated form of either acid at a concentration of 102 mM. The results indicated that the buffer pair formed when the pH was adjusted to 4.5 stabilized the pH of the medium by sequestering protons and by lessening the negative impact of the pH drop on yeast growth, and it also decreased the difference between the extracellular and intracellular pH values (Delta(pH)), the driving force for the intracellular accumulation of acid. Increasing the undissociated acetic acid concentration at pH 4.5 to 163 mM by raising the concentration of the total acid to 267 mM did not increase inhibition. It is suggested that this may be the direct result of decreased acidification of the cytosol because of the intracellular buffering by the buffer pair formed from the acid already accumulated. At a concentration of 102 mM undissociated acetic acid, the yeast grew to higher cell density at pH 3.0 than at pH 4.5, suggesting that it is the total concentration of acetic acid (104 mM at pH 3.0 and 167 mM at pH 4.5) that determines the extent of growth inhibition, not the concentration of undissociated acid alone.

Acetic Acid↗
PubMedDate not supplied

Identification of thiodiglycolic acid, thiodiglycolic acid sulfoxide, and (3-carboxymethylthio)lactic acid as major human biotransformation products of S-carboxymethyl-L-cysteine.

S-Carboxymethyl-L-cysteine (CMC) is used both as an orally administered mucolytic agent and as a probe drug for uncovering polymorphic sulfoxidation of other sulfur-containing drugs in humans. However, several recent studies could not confirm the formation of significant amounts of urinary sulfoxides of CMC or its decarboxylation product S-methyl-L-cysteine. The metabolism of CMC and a 13C-labeled isotopomer was therefore reinvestigated in 11 and 14 humans, respectively, and emphasis was laid on monitoring of potential alternative metabolic pathways. Combined capillary gas chromatography/electron impact or negative-ion chemical ionization mass spectrometry employing stable isotope-labeled analogues as internal standards were used for identification and quantification of CMC metabolites in human urine. Three nitrogen-free metabolites that were identified as thiodiglycolic acid (TDGA, mean: 19.8% of the dose/24 hr), thiodiglycolic acid sulfoxide (TDGA-SO, mean: 13.3% of the dose/24 hr), and (3-carboxymethylthio)lactic acid (TLA, mean: 2.1% of the dose/8 hr), cumulatively account for about one-third of the dose during a urinary collection period of 24 hr. In addition, trace amounts of both TDGA and TLA exist as endogenous components in urine from persons not administered exogenous CMC at levels of about 5 and 1 nmol/ml, respectively. Both major metabolites TDGA and TDGA-SO, that were not considered in previous sulfoxidation phenotyping, are predominantly excreted after 8 hr. These results demonstrate the existence of a pyruvate-like metabolic pathway and suggest the necessity of a revision of the hitherto accepted biotransformation route of CMC in humans.

Biotransformation↗
PubMed1984

[Acid-base equilibrium, blood lactic acid and pyruvic acid in albino rats after muscular exertion under conditions of normal oxygen, hypoxia and hypoxia-hypercapnia].

Albino rats of the Wistar family were subjected at three subsequent equal trials of muscular work: the first in normoxyc conditions; the second in hypoxic normobaric conditions; the third in hypoxic-hypercapnic normobaric conditions. The modifications of the lactacidemia, pyruvicemia and acid-base balance were greatest at the end of hypoxic trial. Added CO2 (2%) sensitively reduced the acidificant effects of the muscular work on the acid-base balance.

Acid-Base Equilibrium↗
PubMed2004

Mechanism of L-lactic acid transport in L6 skeletal muscle cells.

L-lactic acid transport plays an important role in the regulation of L-lactic acid circulation into and out of muscle. To clarify the transport mechanism of L-lactic acid in skeletal muscle, L-lactic acid uptake was investigated using a L6 cell line. mRNAs of monocarboxylate transporter (MCT) 1, 2 and 4 were found to be expressed in L6 cells. The [(14)C] L-lactic acid uptake by L6 cells increased up to pH of 6.0. The [(14)C] L-lactic acid uptake at pH 6.0 was concentration-dependent with a K(m) of 3.7 mM. This process was reduced by alpha-cyano-4-hydroxycinnamate, a typical MCT1, 2 and 4 inhibitor. These results suggest that an MCT participates in the uptake of L-lactic acid by L6 cells. [(14)C] L-lactic acid uptake was markedly inhibited by monocarboxylic acids and monocarboxylate drugs but not by dicarboxylic acids and amino acids. Moreover, benzoic acid, a substrate for MCT1, competitively inhibited this process with K(i) of 1.7 mM. [(14)C] L-lactic acid efflux in L6 cells was inhibited by alpha-cyano-4-hydroxycinnamate but not by benzoic acid. These results suggest that [(14)C] L-lactic acid efflux in L6 cells is mediated by MCT other than MCT1.

Animals↗
PubMed2004

Orientation behaviour of the blood-sucking bug triatoma infestans to short-chain fatty acids: synergistic effect of L-lactic acid and carbon dioxide.

The role of short-chain fatty acids in the host-seeking behaviour of Triatoma infestans larvae was investigated using a locomotion compensator. Several short-chain fatty acids were tested alone over a wide range of doses, or in combination with L-lactic acid (L-LA; 100 microg). Bugs showed no attractive response to single carboxylic acids, but when L-LA was added to airstreams carrying specific intensities of either propionic (C3; 100 microg), butyric (C4; 1 microg) or valeric acid (C5; 1 microg), these mixtures elicited an attractive response, evincing a synergistic effect. No orientation response was observed when caproic acid (C6) was offered with L-LA at the doses tested. Two blends were created: (1) C3, C4 and C5 combined at the effective doses when added with L-LA [C3C4C5 (1)], and (2) C3, C4 and C5 combined at a third of those intensities [C3C4C5 (2)]. Both blends were tested alone, with L-LA (100 microg), with a sub-threshold concentration of CO(2) (300 p.p.m. above the ambient level), and combined with both compounds together. Oriented responses of bugs were only observed with the blend (2) added with L-LA and with the combination of this lure with CO(2). This last combination evoked a behavioural response similar in intensity to that induced by a live mouse.

Animals↗
PubMed2001

Effect of acid resistance of Escherichia coli O157:H7 on efficacy of buffered lactic acid to decontaminate chilled beef tissue and effect of modified atmosphere packaging on survival of Escherichia coli O157:H7 on red meat.

The present study examined the effect of pH-independent acid resistance of Escherichia coli O157:H7 on efficacy of buffered lactic acid to decontaminate chilled beef tissue. A varied level of acid resistance was observed among the 14 strains tested. Eight strains were categorized as acid resistant, four strains as acid sensitive, and two strains demonstrated acid-inducible acid resistance. The survival of an acid-resistant (II/45/4) and acid-sensitive (IX/8/16) E. coli O157:H7 strain on chilled beef tissue treated with 1 and 2% buffered lactic acid, sterile water, or no treatment (control) was followed. A gradual reduction of E. coli O157:H7 was noticed during the 10 days of storage at 4 degrees C for each of the treatments. Decontamination with 1 and 2% buffered lactic acid did not appreciably affect the pathogen. Differences in the pH-independent acid resistance of the strains had no effect on the efficacy of decontamination. The effect of modified atmosphere packaging (MAP) on survival of E. coli O157:H7 in red meat was also studied. MAP (40% CO2/60% N2) or vacuum did not significantly influence survival of E. coli O157:H7 on inoculated sliced beef (retail cuts) meat compared to packing in air. The relative small outgrowth of lactic acid bacteria during storage under vacuum for 28 days did not affect survival of E. coli O157:H7. Neither lactic acid decontamination nor vacuum or MAP packaging could enhance reduction of E. coli O157:H7 on beef, thus underlining the need for preventive measures to control the public health risk of E. coli O157:H7.

Adaptation, Physiological↗