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At least 217 records · Page 12Linked to original sources
PubMed1987

Analysis of volatile fatty acids in biological specimens by capillary column gas chromatography.

A method was developed to analyze and quantify volatile fatty acids (VFA) such as acetic, propionic, butyric, isobutyric, valeric and isovaleric acids in biological specimens. To obtain good sample transfer into the chromatographic system an organic solvent had to be used together with an aqueous milieu, thus improving wetting properties of the liquid sample plug introduced into the column. Sample preparation was carried out under alkaline conditions in order to exclude or minimize sample losses due to sample transfer during the extraction and work-up procedure. A cold on-column injection was applied to avoid irregular discrimination of the various acids due to sample splitting and an automatic injection technique was used to accommodate the large number of samples generated from biological origin. Connection of a pre-column of wide internal diameter (0.53 mm) to the analytical column (0.32 m) was optimized and adapted to the nature of the injection solvent mixture consisting of acetonitrile, water and hydrochloric acid. To obtain well-separated and correctly quantifiable gas chromatographic peaks, it was essential to perform the chromatography under acidic aqueous conditions. Standard resolution conditions and response factors were evaluated. The chromatographic results of applying this method to biological specimens from both rats and humans are provided.

Animals↗
PubMed1980

Origin and utilization of volatile fatty acids in the rat.

The arteriovenous differences in the caecum of the rat have been compared for volatile fatty acids (VFA) and for electrolytes. Our results suggest the possibility of an exchange between VFA and chloride at the level of the caecal wall, rather than a net exchange between VFA and bicarbonate; however, the role of bicarbonate or Cl- at the cellular level is still unknown. Acetate uptake by the liver was enhanced when acetate in the afferent plasma was increased in fed as in starved rats, showing that acetyl CoA synthetase was still active during starvation. A release of endogenous acetate was only observed in situations of very active ketogenesis (starvation at the end of pregnancy). In physiological conditions, propionate and butyrate reaching the liver were almost quantitatively removed. However, butyrate was taken up by the liver at a higher rate than propionate after intracecal loads. Propionate was very efficiently utilized as a glucogenic substrate and without noticeable disturbance of lactate metabolism. After administration of acetate loads in starved rats, hepatic ketogenesis increased slightly. There was a marked difference between ketogenesis from butyrate in fed and starved rats. The low ketogenesis from butyrate in the fed rats stressed the important role of metabolic pathways of acetyl-CoA utilization in the control of ketogenesis. In contrast to alanine or lactate, propionate was poorly antiketogenic in the rat.

Acetates↗
PubMed1989

[Production of volatile fatty acids in the rumen of calves during dietary-microbial stimulation and early weaning].

The contents of volatile fatty acids in the rumen fluid were studied in calves at an early (seven weeks of age) and traditional weaning term (nine weeks of age). Weaning at the age of seven weeks enabled to save 16.2 kg of milk replacer per calf; there was also a lower content of concentrates in the starter feed with a supplement of Amylastim. The health condition of the calves was good in both groups. The average daily weight gains for the period from the second to the ninth week of age were 0.550 kg in the early weaned calves and 0.690 kg in the calves weaned at a normal time. Early weaning had a positive influence on the development of rumen metabolism. Calves weaned at the age of seven weeks, compared with those weaned at the age of nine weeks, had much higher concentrations of VFA (p less than 0.05) in rumen fluid (at the age of seven weeks: 130.49 mmol per litre vs. 111.53 mmol per litre; at the age of eight weeks: 119.74 mmol per litre vs. 96.98 mmol per litre). Early weaned calves had the statistically significantly (p less than 0.05) higher proportions of propionic acid, butyric acid, i-butyric acid, and valeric acid. Later-weaned calves had the significantly higher (p less than 0.05) contents of acetic acid and i-valeric acid.

Animal Feed↗
PubMed2005

Removal of volatile fatty acids with immobilized Rhodococcus sp. B261.

The removal of aqueous volatile fatty acids (VFA) in wastewater and spoiled waste-foods by immobilized Rhodococcus sp. B261 was investigated. The n-valeric acid (0.5%) was completely removed within 25 h under the following conditions; solution pH, 8.0; air flow rate, 0.2 l/min; superficial velocity, 0.96 h(-1); temperature, 37 degrees C. Under the optimized conditions, the acetic (8525 ppm), propionic (7310 ppm) and n-butyric (4360 ppm) except n-valeric (2572 ppm) acids from the wastewater were completely removed by immobilized Rhodococcus sp. B261 in 24 h. The acetic (7810 ppm), propionic (8942 ppm) and butyric (5730 ppm) acids from the solution of spoiled waste-foods were effectively removed by immobilized Rhodococcus sp. B261 from 48 h within 60 h but n-valeric acid (3625 ppm) took 72 h.

Acetic Acid↗
PubMed1981

Volatile fatty acids in human peripheral and portal blood: quantitative determination vacuum distillation and gas chromatography.

In order to determine volatile fatty acids (VFA) in human blood, gas chromatographic analyses were performed after blood samples had been pre-treated by a vacuum distillation procedure with subsequent evaporation. Results of the reproducibility study, investigated by pre-treating five aliquots of one human serum sample showed C.V. values ranging from 7.4 to 18.2. Normal serum VFA values were determined in individual serum samples collected from healthy subjects and compared to those present in serum from patients undergoing gall-bladder surgery. The serum VFA values were comparable in the two groups. In the surgical patients, blood was also collected from the portal circulation. All portal serum VFA values, except that of iso-butyric acid, were higher than those found in the samples collected from the peripheral arm vein. VFA values were also determined in serum specimens obtained from blood collected from the arm vein of patients with extensive cirrhosis of the liver. The VFA values showed marked individual variations and were higher than those found in peripheral samples from healthy subjects and patients undergoing gall-bladder surgery, but were lower than those found in samples from the portal circulation from the surgical patients.

Arm↗
PubMed1996

Excitatory effects of volatile fatty acids on the in vitro motility of the rumen of sheep.

The effects of 1 to 100 mM volatile fatty acids (VFA) on the cranial dorsal rumen musculature of sheep were examined in vitro. Sodium acetate, sodium propionate and sodium butyrate, either singly or as a mixture, stimulated marked dose-dependent contractions of longitudinal muscle (LM) and internal oblique muscle (IOM). The threshold concentration was between 1 and 3 mM depending on the VFA and the muscle tissue and the responses were modified by the presence of the mucosal epithelium. The responses to VFA were significantly decreased by atropine (10(-6) M) and tetrodotoxin (10(-7) M) but were unaffected by hexamethonium (10(-3) M). Indomethacin (10(-6) M) modified the responses, suggesting that prostaglandins may also be involved. Acetic, propionic and butyric acids also stimulated dose-dependent contractions of LM and IOM. After having been stimulated with 100 mM acids the preparations became refractory to further stimulation by acetylcholine. It is concluded that in vitro the acid and salt forms of VFA excite contractions of the rumen by both cholinergic and non-cholinergic mechanisms.

Acetylcholine↗
PubMed1998

Inactivation of Salmonella typhi by high levels of volatile fatty acids during anaerobic digestion.

Survival of Salmonella typhi was investigated in an anaerobic digester for cattle dung with volatile fatty acid (VFA) levels of 5000 mg l(-1) and pH 6.0. The organism was added to the digester only once in the first experiment and daily in the other. Survival was monitored on alternate days. In the single dose experiment, the counts of Salm. typhi declined rapidly and the pathogen was completely eliminated within 12 d in the experimental digester (VFA ca 5000 mg l(-1) and pH 6.0), whereas 26 d were required in the control digester (VFA ca 100 mg l(-1) and pH 6.8). T90 values for the experimental and control digesters were 2.44 d and 4.80 d, respectively. In the daily dose experiment, a four log reduction in the pathogen count was observed in the experimental digester, but only a two log reduction in the control digester at the end of the experimental period. The mean T90 values for the experimental and the control digester were 4.22 d and 18.63 d, respectively. In both the experiments, statistical analysis of the data showed significant differences in the survival pattern of Salm. typhi in the two digesters.

Anaerobiosis↗
PubMed1978

Absorption of inorganic ions and volatile fatty acids in the rabbit caecum.

1. Rabbit caecal segments in situ were used to measure absorption rates of volatile fatty acids (VFA) and inorganic ions from a saline solution comparable in composition to normal caecal fluid. 2. Results confirm the importance of VFA absorption from caecal material found by other workers. 3. Like the mammalian colon, the rabbit caecum conserved large amounts of sodium, chloride and water. Bicarbonate was also absorbed. 4. VFA replacement studies showed that net water absorption was reduced, net electrolyte absorption was hardly influenced. 5. Na replacement completely inhibited net water absorption and decreased net VFA and Cl absorption, HCO3 was heavily secreted. 6. These findings indicate that VFA absorption in the rabbit caecum is partly dependent on Na absorption and that in the absence of Na an anion-exchange mechanism occurs.

Animals↗
PubMed2002

The effects of change in volatile fatty acid (VFA) composition on methanogenic upflow filter reactor (UFAF) performance.

The effects of changes in composition of a volatile fatty acid mixture (namely acetic, propionic and butyric acids) fed to a methanogenic upflow filter reactor (UFAF) were investigated in terms of reactor chemical oxygen demand (COD) removal efficiency and biogas production level. A mixed substrate consisting of differing proportions of VFAs (on a COD basis) was fed to the reactor in semi-continuous mode under constant organic loading rate (OLR) and hydraulic retention time (HRT). At an OLR of 1.2 kg COD m(-3) x d and HRT of 4 days, increasing propionic acid concentrations of about 312 mg l(-1), 617 mg l(-1), 951 mg l(-1) and 1242 mg l(-1) fed to the reactor provided COD removal rates and biogas production levels of, 84.70%-1301 ml d(-1), 80.80%-1214 ml d(-1), 73.65%-1071 ml d(-1) and 65.53%-942 ml d(-1), respectively, indicating inhibitory effects of propionic acid on the methanogenic ecosystem. Subsequent introduction of butyric acid (247 mg l(-1)) in addition to propionic acid (891 mg l(-1)) increased the performance of the UFAF, yielding 76.10% COD removal and 1075 ml d(-1) of biogas production. The instability observed in the system towards the end of the study probably originated from operating the reactor at relatively high VFA concentrations for a long period of time. Change in VFA composition did not seem to have significant effects on the effluent MLVSS/MLSS ratio. The upflow anaerobic filter reactor adapted to variations in feed composition in a short period of time.

Bacteria, Anaerobic↗
PubMedDate not supplied

[Quantitative gas chromatographic determination of volatile fatty acids in express diagnosis of nonclostridial anaerobic infection].

Gas chromatographic procedure was used for quantitative estimation of metabolic [volatile fatty acids (C2-C6)] of anaerobic bacteria in express diagnosis of nonclostridial anaerobic infection in surgical patients with purulent bacterial destruction of lungs and with abdominal impairments as well as in patients with calculous cholecystitis. Only traces of acid metabolites were detected in donor blood. A 10-30-fold increase in their content in blood of patients with surgical and gynecologic sepsis enabled to diagnose the anaerobic form of the disease.

Bacteria, Anaerobic↗
PubMed1982

[The efficiency of hexose energy transformation into energy for volatile fatty acid production in the rumen of sheep fed diets containing sawdust].

Based on the production and interrelationship of volatile fatty acids (VFA), the mathematical method according to Orskov et al. (1968) was used to determine the efficiency of VFA production, and/or conversion of the energy of hexoses contained in fodders into VFA energy in rumen. VFA were separated by gas chromatography. The energy yield of VFA production in the rumen contents of wethers was averaged from the samples taken one, three and five hours after feeding. Whethers were fed 11 experimental diets, in which a part of bulk fodder (5-20%) was replaced by treated or untreated sawdust, and/or a diet without sawdust. The energy yield varied from 73.12 to 76.51% and the maximum values were achieved with the diets containing no sawdust. Compared with the diets with sawdust addition, the differences are statistically significant (P less than 0.05). The addition of the treated beech sawdust to the same diet, in comparison with untreated sawdust resulted in a higher energy yield of VFA production, however, with no statistical significance. The ratio of acetate to propionate was in a direct but negative relationship to energy yield of VFA production (n = 44, r = -0.905, P less than 0.001). Therefore the diets rich in cellulose, which cause an increase in the molar percentage of acetic acid and a subsequent increase in the ratio of acetate to propionate, might be responsible for the energy losses in the form of methane and can result in the decrease in total energy balance (Orskov et al., 1968).

Animal Feed↗