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The white-tailed rat Mystromys albicaudatus (A. Smith, 1834) has a sacculated bilocular hemiglandular stomach. Its forestomach resembles a rumen, in that it has papillae and a high density of bacteria. This suggests that the forestomach of the white-tailed rat may be functionally similar to a rumen. Although the fermentation of fibre is very limited in the digestive tract of the white-tailed rat, the determination of total foregut fermentation relative to caecal fermentation was essential since ingested soluble carbohydrates may also be fermented by the forestomach bacteria. The present study investigated the effects of different diets (varying in proximate composition) on the pH, volatile fatty acid and lactic acid production for the various regions of the gut. The results indicate that M. albicaudatus is essentially a hindgut fermenter.
The aim of the study was to assess usefulness of the LIVE/DEAD fluorescent staining method and gas chromatography to monitor the viability and metabolic activity of Propionibacterium strains in long-term cultures in milk. The effect of 4% NaCl addition and a temperature of 10°C on the growth of Propionibacterium freudenreichii ssp. freudenreichii 111, 109C, 108 strains was studied for 28 days. Bacterial cells were assessed in cultures by microscopic and plate counting methods in regular intervals. The cultures were additionally determined for the content of volatile fatty acids: C2 to C7. The total cell counts of all strains in cultures assessed by the microscopic method were noticed to be 1 to 5 logarithmic cycles higher in comparison to those determined with the plate counting method. In following days and weeks of culture, increasing discrepancies were observed between the results obtained using microscopic and plate methods. Both methods revealed similar trends in the viability of strains under control conditions and a little impact of NaCl addition on cell growth and decrease. The cultures run at a temperature of 10°C exhibited different course of growth and decline of the number of monitored populations depending on strain and method applied. Individual strains possessed different acid formation activity. From the beginning of incubation, the highest concentrations were reported for propionic and acetic acids, whereas the other acids in number from 4 to 6 appeared subsequently. The temperature of 10°C inhibited acids formation by all strains, whereas 4% addition of NaCl stimulated the acid-forming activity and during incubation under those conditions the contents of volatile acids were recorded to be the highest.
Volatile fatty acids (VFAs) are present in environmental waters in the range of 1 to 5,000 ppm and different methods have been reported for their determination. In this paper we have studied and compared analytical performance parameters for the distillation method followed by potentiometric titration, spectrophotometric and gas chromatographic methods. The main disadvantage of the distillation approach was quite poor absolute recovery (53-58%) from the given matrix and rather elevated limit of quantification (LOQ) at 110 mg/L. Direct potentiometric titration was characterized by acceptable accuracy (above 97%) and precision in the range 1.8%-15%. The LOQ value was 11 mg/L. The spectrophotometric method was sensitive for hydrogen carbonate alkalinity and phosphate ions; measured concentrations of acetic acid were lower than nominal. The precision and accuracy of the spectrophotometric method were in the ranges 1.3-14% and 82.1-104.2%, respectively. Limit of quantification was 28 mg/L. However, if ion exchange bed is used prior to this method the LOQ can be reduced to 5 mg/L. The GC method is characterized by quite low LOQ (5 mg/L) and seems to be the best methodology to determine low VFA concentrations in environmental waters. The precision of the method ranged from 5.7 to 14.8% and accuracy was above 92%. Additionally, this method allows for determination of individual VFAs.
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