Higher Final Concentration Research Articles

The effect of yeast extract supplementation on the production of lactic acid from whey permeate byLactobacillus helueticus

Batch and continuous two-stage cultures have been conducted in order to determine the effect of yeast extract (YE) on the homolactic fermentation of whey permeate byLactobacillus helveticus. Supplementation with YE had a significant effet on lactic acid concentration, volumetric productivity, and substrate conversion, but not on lactic acid yield. Volumetric productivity in the first stage increased from 2 to 9 g l−1 per hour by increasing the YE concentration from 1.5 to 25 g l−1 At the same time conversion improved from 22% to 93% at a dilution rate of 0.2 h−1. The second stage demonstrated the effect of YE at a lower dilution rate (0.14 h−1. A high system conversion (97%) and a high final lactic acid concentration (40 g l−1) were achieved with 10 g l−1 YE.

Sublethal responses to endrin in sediment by Limnodrilus hoffmeisteri (Tubificidae), and in mixed-culture with Stylodrilus heringianus (Lumbriculidae)

Sediment reworking by Limnodrilus hoffmeisteri (Tubificidae) alone, and with Stylodrilus heringianus (Lumbriculidae) were measured in sediments dosed with endrin by monitoring the burial of a 137cesium marker layer. Endrin concentrations ranged from 16.1 to 81 400 ng/g dry sediment weight. Alterations in reworking rates were observed at sediment concentrations two to five orders of magnitude below LC 50 values. In single species experiments with L. hoffmeisteri at low endrin concentrations, marker layer burial rate data did not suggest stimulation of reworking, as had previously been found for S. heringianus. At higher concentrations, reworking rates were equal to or slower than control rates early in experiments, followed by dramatic decreases thereafter. Reworking rates with mixed species (1:1 species ratio) suggested that the presence of S. heringianus enhanced the reworking response of L. hoffmeisteri. Post-experimental worm dry weights were inversely related to high sediment concentrations for both species. Reductions in post-experimental L. hoffmeisteri mortalities and increases in L. hoffmeisteri dry weights in mixed species tests at high endrin concentrations implied that L. hoffmeisteri benefits from the presence of S. heringianus, although the reverse was not observed. High final sediment endrin concentrations in the upper three cm implied worm mediated upward contaminant transport. Bioaccumulation factors for S. heringianus ranged from 9.7 to 43.8 and were consistently three to four times greater than bioaccumulation factors for L. hoffmeisteri (1.7 to 13.6).

Sublethal responses to endrin in sediment by Stylodrilus heringianus (Lumbriculidae) as measured by a 137cesium marker layer technique

Sediment reworking rates of Stylodrilus heringianus (Oligochaeta: Lumbriculidae) were measured in microcosms containing sediments dosed with the chlorinated pesticide, endrin. Reworking rates were measured at 10°C by monitoring a 137cesium marker layer burial in contaminated and uncontaminated microcosms. Endrin concentrations ranged from 3.1 to 42 000 ng/g dry sediment. Alterations in reworking rates were observed at sediment concentrations five and one half orders of magnitude below the LC 50 (1 650 μg/g). For the lower concentrations, marker layer burial rate data suggested possible stimulatory effects in the first 300 to 600 h, followed by significant rate decreases relative to controls. For higher concentrations, rates were equal to or slower than control rates in the first 600 h, followed by dramatic decreases in the last 600 h. High final surficial sediment endrin concentrations at the end of experiments implied worm mediated upward transport. Worm mortalities were 9.3 to 28% for the two highest concentrations (42 000 and 11 500 ng/g) and 0 to 6.7% for all other concentrations including controls. Post experimental worm dry weights were inversely related to high concentrations. Bioaccumulation factors ranged from 34 to 67 on a g dry organism to g dry sediment basis.

Ethanol extraction of red peppers: kinetic studies and microstructure

SummaryA three‐parameter kinetic equation was developed for ethanol extraction of oleoresin from dry red peppers under different solute to solvent ratios, particle sizes and condition of structural damage. The model distinguished two main mechanisms of extraction: a fast, washing step and a diffusion‐controlled process. Flaking and, to a lesser extent, blanching induced significant cellular damage resulting in more oleoresin being washed, a faster extraction rate and a higher final concentration in the solvent, compared to untreated material. The activation energy for extraction derived from the study was 6.1 kcal/mol, typical of diffusion‐controlled processes. Light micrographs related microstructure to variations in extraction parameters.

Optimization of process design for continuous ethanol production by Zymomonas mobilis ATCC 29191

A two-stage continuous-stirred-tank-reactor (CSTR) system is used to achieve high final alcohol concentrations (>100 g/l) with Zymononas mobilis ATCC 29191. By employing continuous cell recycle on the second stage CSTR of a two-stage process a high overall volumetric productivity (18.13 g/l/h) is achieved together with >100 g/l effluent alcohol.

Isolation and characterization of leukaemic B-lymphocytes: Influence of anticoagulant on C3-receptor detection, humoral killing and capping of cell surface immunoglobulin

Guinea pig L 2C neoplastic B-lymphocytes processed from leukaemic blood collected into EDTA as anticoagulant exhibited high affinity rosetting for EAC mouse indicator cells. Partial blocking of the C3-receptors was apparent with blood collected into heparin or citrate as anticoagulant. This could be minimized by keeping the temperature at 4°C and avoided by ensuring a high final concentration of citrate (⩾40 mM). Results from experiments in vitro suggested that receptor blocking may have been a consequence of complement activation by the L 2C cells occurring via the alternative pathway. No injury to the cells was evident with any of the anticoagulants used, and their susceptibility to antibody-dependent complement-mediated lysis was independent of anticoagulant and unaffected by the irregular presence of membrane-bound C3. In experiments where the antibody-induced redistribution of L 2C surface immunoglobulin was investigated, it was found that cells processed from blood collected into EDTA showed poor ability to cap and interiorize their surface immunoglobulin in comparison with cells processed from heparinized or citrated blood. Inhibition of capping was found to be dependent on the concentration of EDTA and could be avoided by collecting blood into a large volume of low molarity EDTA as opposed to a small volume of high molarity EDTA. Some practical and theoretical consequences of our observations are discussed.

Inhibition of Cholesterol Biosynthesis and Acetyl-Coenzyme A Synthetase by Bovine Milk and Orotic Acid

Pasteurized, homogenized bovine milk or orotic acid in solution at final concentrations varying from 3.3μM to 322μM in rat liver homogenates inhibited the incorporation of [1-Carbon 14] acetate but not [1-Carbon 14] acetyl-coenzyme A, 3-hydroxy-3-methyj-[Carbon 14] glutaryl-coenzyme A or [5-hydrogen 3] mevalonic acid into cholesterol. Milk inhibited cholesterol biosynthesis up to 72±10% before acetyl-coenzyme A formation, thus indicating that acetyl-coenzyme A synthetase is the affected enzyme. Kinetics of the inhibition were studied with acetyl-coenzyme A synthetase purified from yeast. From a Line-weaver-Burk plot of the inhibition of yeast acetyl-coenzyme A synthetase, orotic acid is a noncompetitive inhibitor of acetyl-coenzyme A synthetase. A Michaelis constant was 6.0×10−4 M for acetate with the yeast enzyme while a Ki was 6.6×10−5 M for orotic acid. The approximate point of 50% inhibition with rat liver enzyme was 7×10−6 M orotic acid indicating the mammalian enzyme may be more sensitive to the orotic acid. Nicotinic acid also inhibited the yeast enzyme. Fifty percent inhibition required a relatively high final concentration–about 12mM. Neither raw milk nor pasteurized, homogenized milk inhibited 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase that had been partially purified from rat liver.

Mutagenicity tests with trypaflavin and hexamethylenetetramine in mammals in vivo and in vitro

In our experiments we first tested the ability of different concentrations of trypaflavine and hexamethylenetetramine to induce dominant lethal mutations by injecting the compounds intraperitoneally or orally into male mice. Only for high dosages the induction of dominant lethals could be ascertained (50 mg trypaflavine per kg body weight and 25000 mg/kg hexamethylenetetramine). No specific sensitivity of single stages of the cycle of spermatogenesis was observed. It could be demonstrated by fluorescence microscopy that trypaflavine invades the male germ cells. Further indications for the weak mutagenicity of this compound we received cytogenetically by finding some chromosome aberrations and increased rates of univalents in diakinesis. In vitro investigations with hexamethylenetetramine in high final concentrations used in the mice experiments induced cell death, depression of mitosis and clumping of chromosomal material in blood cells as well as in HeLa cell cultures. Lower concentrations tested on HeLa cells were found to induce a number of chromosomal aberrations, but in a certain dosage, only (1×10-3M). No chromosome changes could be recognized in blood or HeLa cell mitosis when hexamethylenetetramine was given in final concentrations 1×10-4M and lower. A comparison of the used concentrations of the test substances and their mutagenic efficiency with the usual therapeutic dosages give rise to assume that the genetic risk for man is low for both drugs.