Search Results

You are looking at 81 - 90 of 107 items for

  • Author or Editor: et al. x
  • Refine by Access: All Content x
Clear All Modify Search

Fungi, in particular Aspergilli, are well known for their potential to overproduce a variety of organic acids. These microorganisms have an intrinsic ability to accumulate these substances and it is generally believed that this provides the fungi with an ecological advantage, since they grow rather well at pH 3 to 5, while some species even tolerate pH values as low as 1. 5. Organic acid production can be stimulated and in a number of cases conditions have been found that result in almost quantitative conversion of carbon substrate into acid. This is exploited in large-scale production of a number of organic acids like citric-, gluconic- and itaconic acid. Both in production volume as well as in knowledge available, citrate is by far the major organic acid. Citric acid (2-hydroxy-propane-1, 2, 3-tricarboxylic acid) is a true bulk product with an estimated global production of over 900 thousand tons in the year 2000. Till the beginning of the 20th century, it was exclusively extracted from lemons. Since the global market was dominated by an Italian cartel, other means of production were sought. Chemical synthesis was possible, but not suitable due to expensive raw materials and a complicated process with low yield. The discovery of citrate accumulation by Aspergillus niger led to a rapid development of a fermentation process, which only a decade later accounted for a large part of the global production. The application of citric acid is based on three of its properties: (1) acidity and buffer capacity, (2) taste and flavour, and (3) chelation of metal ions. Because of its three acid groups with pKa values of 3. 1, 4. 7 and 6. 4, citrate is able to produce a very low pH in solution, but is also useful as a buffer over a broad range of pH values (2 to 7). Citric acid has a pleasant acid taste which leaves little aftertaste. It sometimes enhances flavour, but is also able to mask sweetness, such as the aspartame taste in diet beverages. Chelation of metal ions is a very important property that has led to applications such as antioxidant and preservative. Moreover, it is a “natural” substance and fully biodegradable.

Restricted access

Difficulties in measuring the urea content in sheep's milk often occur with spectral photometry due to the high protein and fat concentrations of the milk. In this study an enzymatic flow procedure (QuickChem 8000 Ion Analyser, Lachat Instruments, Milwaukee, USA) to determine the urea content in ovine and bovine milk was evaluated. Urea content is determined by the Berthelot reaction after splitting it enzymatically with urease. The free ammonia diffuses through a teflon membrane into a stream of reagent solutions. Detection takes place by means of a reaction between the ammonium ions with hypochlorite and salicylate producing a green colour, which is measured spectrometrically in a flow meter at 660 nm. By using a diffusion cell chemical deproteinisation of milk is not necessary and capacity is high. The assessed procedure exhibited high accuracy and precision and reached a sample capacity of 55 samples an hour. Storage of the milk samples for several days as well as chemical preservation with bronopol had no effect on the measurement procedure. Due to the complexity of the apparatus and the costs associated therewith, the device proves less suitable for routine diagnostics but rather serves as a reference method for the measurement of urea concentration in milk.

Restricted access

Polymerase chain reaction (PCR) was used to amplify the spacer regions between the 16S and 23S genes of rRNA genetic loci of Salmonella serovars for their rapid identification. These genetic loci revealed a significant level of polymorphism in length across the species/serovar lines. When the 16S-23S spacer region amplification products were subjected to agarose electrophoresis, the patterns observed could be used to distinguish all the serovars of Salmonella tested. Unique elements obtained in amplification products were mostly clustered at serovar level, although certain genus-specific patterns were also observed. On the basis of the results obtained, the amplification of 16S-23S ribosomal spacer region could suitably be used in a PCR-based identification method for Salmonella serovars.

Restricted access

In addition to the original equipment, a new measuring set has been constructed for observing the atmospheric electric potential gradient (PG) at Nagycenk station. The study describes this new set and reports on PG variations derived from data obtained by the two simultaneous measurements. Both runs of the mean diurnal variations determined on the basis of the two data sets are quite similar, as well as they resemble the appropriate diurnal variation derived from earlier Nagycenk data, or fairly the `Carnegie Curve'. Nevertheless, the measured PG level is somewhat higher in the case of the new equipment (PG 2) than that measured with the original set (PG 1). This is also true in the case of single days diurnal variations, however, the daily runs derived from the individual measurements are hardly different. Whichever of the two data sets is applied, the PG's seasonal (annual) variation shows a distinct maximum in winter, even if this maximum is again higher for PG 2 than that for PG 1. Certain ideas on this behaviour are also suggested by the study

Restricted access

Bovine torovirus is an established aetiological agent of disease in cattle, while porcine torovirus has only been isolated from healthy animals. Evidence for the presence of torovirus has been described in several European countries and also in the United States. A survey was performed to detect toroviruses in Hungary by means of sampling ten swine and nine bovine herds. Rectal swabs and faecal specimens were collected from diarrhoeic calves and from weaned piglets. The samples were tested by the reverse transcription-polymerase chain reaction (RT-PCR) using torovirus-specific primers and the positive samples were further examined by electron microscopy (EM). Torovirus was detected in 4 diarrhoeic calves (out of 111) and in 10 healthy weaned pigs (out of 200 tested), representing two of the 9 calf herds and two of the 10 pig herds tested. This is the first report of exact diagnosis of torovirus in Hungary.

Restricted access

For the investigation of diversity-productivity relationships under natural conditions, we present an operationally feasible measurement scheme explicitly considering the spatial organization of vegetation. We hypothesised that the spatial arrangement of the coexistence of species influences patch-level productivity. To characterise diversity, co-occurrences of species were recorded along oval transects allowing scaling by aggregation between 5 cm and 25 m. Productivity was characterised by field radiometric measurements, calibrated for leaf area and biomass, arranged in a sampling scheme scalable between 20 cm and 50 m. All data were collected along a slight resource gradient in the Stipa-Bouteloua (upland) community of the northern mixed-grass prairie in Grasslands National Park, Saskatchewan. We found a wide range of correlations (Kendall's . between -0. 2 and 0. 9) between various measures of diversity (species richness, local species combinations) and productivity (average and variability of leaf-area index) as a function of sampling unit size. For field assessment of patch-level composition and functioning, we recommend to use samples at the spatial resolution corresponding to the maximum number of local species combinations as an appropriate scale for comparison. We demonstrate how our sampling methodology can be considered for possible process-oriented inference about diversity and productivity. To characterise diversity-productivity relationships for long-term monitoring and prediction of plant community structure and functioning, scalable, repeatable, non-destructive observations should be applied.

Restricted access

The inability of traditional risk factors such as hypercholesterolemia, hypertension, and smoking to explain the incidence of atherosclerosis (AT) in about 50% of the cases prompted a  search for additional putative risk factors involved in the development of the disease. Infectious agents have long been suspected to initiate/contribute to the process of AT. It has also been suggested that inflammation, either related to infectious agents or independent from infection,  may mediate the atherogenic process [1, 2].

Restricted access

The aim of the present study was to develop a treatment supporting the membrane of ram spermatozoa. Semen of different ejaculates collected from breeding rams was mixed andsamples of 109 sperm cells per ml and Tris-egg yolk extender were completed with the following antioxidants: a-tocopherol acetate (E), glutathione peroxidase (GP), Aromex® (AR), resveratrol (R), resveratrol + vitamin E (RE), resveratrol + Aromex® (RAR), resveratrol + GP (RGP). Peroxidation was evaluated by the analysis of malondialdehyde (MDA) during incubation for 30, 60 and 120 min at 37°C as well as during a 24-h incubation at 5°C. The success of preservation was checked in a 9-day-long period by observing the acrosomal defects and the motility of spermatozoa. Concentration of MDA was 4.06 nmol/109 spermatozoa in samples treated with 15 µg R while the control sample contained 69.79 nmol MDA per 109 spermatozoa after 24-h incubation. Following 30-, 60- and 120-min storage the concentration of MDA in control and R-treated samples was 25.89, 36.91, 49.57 and 3.69, 3.74, 3.74 nmol/109 spermatozoa, respectively. Moreover, a significantly higher proportion of motile sperm cells was observed in the treated than in the control samples. The frequency of acrosomal defects was lower in the treated groups than in the control. These results indicate that RAR treatment can improve the effects of ram semen preservation.

Restricted access

In the following investigations, the LH secretion of cells from pituitaries in heifers on days 16-18 of their oestrous cycle (n = 14) was analysed. Cells were dissociated with trypsin and collagenase and maintained in a static culture system. For the estimation of LH release, the cells were incubated with various concentrations of mammalian GnRH (Lutrelef) for 6h. To determine the action of Antarelix (GnRH antagonist), the cells were preincubated for 1 h with concentrations of 10-5 or 10-4 M Antarelix followed by 10-6 M GnRH coincubation for a further 6h. At the end of each incubation, the medium was collected for LH analysis. Parallel, intracellular LH was qualitatively detected by immunocytochemistry. Changes in the intensity of LH staining within the cells in dependence of different GnRH concentrations were not observed, but a significant increase LH secretion in pituitary cells was measured at 10-6 M GnRH. Antarelix had no effect on basal LH secretion at concentrations of 10-4 and 10-5 M. After coincubation of pituitary cells with Antarelix and GnRH, Antarelix blocked the GnRH-stimulated LH secretion with a maximal effect of 10-4 M, but the staining of immunoreactive intracellular LH was detected at approximately the same level compared to the pituitary cells treated with exogenous GnRH alone. These data demonstrate that Antarelix is effective in influencing the GnRH-stimulated LH secretion of pituitary cells in vitro. After administration of Antarelix in vivo, the GnRH-stimulated LH secretion of cultured pituitary cells was not inhibited.

Restricted access

Species richness, the location of exotic species and heterogeneity (investigated via dissimilarity and via species-area relations) were investigated in relation to spatial scale, in an ecotone between Nothofagus forest and sub-alpine shrubland. The rate of change in ordination score as well as tree diameter and the dripline were used to locate the position of the ecotone. Patterns of species richness were largely scale-independent, with species richness lowest in the forest community, intermediate in the ecotone, highest a short distance into the shrubland, and lower again in the shrubland further from the ecotone. High richness just into the shrubland is attributed to the existence of a fine-scale spatial mosaic pattern of vegetation, though the spatial mass effect may have a role. Exotic species were absent in the forest, but occurred sparsely in the ecotone and in the shrubland, possibly with decreasing frequency away from the ecotone. Community pattern, expressed by species-based dissimilarity and species-area curves, also differed. The ecotone community was the most heterogeneous (indicated by higher dissimilarity values and a steeper species-area slope with higher Arrhenius z-values), with the forest the least heterogeneous and the shrubland intermediate. We conclude that z-values are inter-woven with both habitat and spatial scale, and that this argues against a universal relationship between species and area.

Restricted access