Volatile fatty acids areanaerobic digestionImportance of processIntermediate productMethane bacteria mainly use VFA to form methane, and only a small part of methane is produced by COtwoAnd HtwoBuild.But COtwoAnd HtwoThe formation also goes through the intermediate process of polymer organic matter forming VFA.Therefore, the formation of methane is inseparable from the formation of VFA, but VFAAnaerobic reactorThe accumulation in can reflectMethanogenThe inactive state of orReactorOperating conditionsThe higher concentration of VFA (such as acetic acid) is harmful to methanogensinhibition。Therefore, the effluent VFA is used as an importantControl indicators。
In animals, linear acetic acidpropionic acidAnd butyric acid, about B, P and butyric acidrumenFermentation VFAtotal outputAnd acetic acid production is the largest, accounting for 70% - 75% of the total VFA production.The proportion and quantity of volatile fatty acids in different animals are different, as shown in Figure 1.Volatile fatty acids can not only be used asRuminantenergy metabolismIt also has many regulating functions.[1]
VFA in real stomach can inhibitContractility, so highConcentrateUnder feeding conditions,abomasumIt is one of the ways that high concentrate feed can induce regurgitation disease that internal VFA reflexively inhibits regurgitation.[1]
Effect on endocrine
motilinIt is related to the physiological regulation of stomach movement, and can cause stomach andduodenumStrong contraction, promotingGastric emptying, StimulatingPepsin、Pancreatic juiceSecretion, gallbladder contraction, enlargementgastric mucosablood flow。Duodenal acidification or alkalization can stimulate motilin release.Infusion of VFA can increase the plasma motilin level in goatsrumenInternal infusionacetic acid、propionic acidMotilin level increased after butyric acid;However, acetic acid, propionic acid, butyric acid (except acetic acid) andcontrol groupThe difference is significant.VFA pairinsulinIt also has an impact.[1]
Dietary effectsMilk fat rateMechanism andrumenVFA changes in the rumen cause metabolic changes.[1]
Impact on disease
VFA is intestinal inhibitionPathogenic MicrobesIt can be inhibited when VFA concentration increasesSalmonellaThe ability of inhibiting pathogenic microorganisms in the intestine is also related to pH value, and the pH value in the intestine is related to VFA content.[1]
rumenThere is a certain relationship between the internal volatile fatty acids and methane production.[1]
influence factor
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The generation and proportion of VFA are not only related to the feed itself, but also affected by other factors, including mineralsIonic carrier, animal age and feeding timeOrganic matter, outflow velocityEnzyme preparation, Chinese herbal medicinehealthEtc.[1]
Absorption metabolism
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stayRuminantAcetic acid, propionic acid and butyric acid are absorbed from the rumen wall, which is the main source of energy for ruminants.Many factors will affect the absorption of these volatile fatty acids, such as the concentration and proportion of VFArumenpH、Rumen epithelial bloodLiquidityEtc.The absorption of glucose by ruminants does not come from the rumen or small intestine, but mostly depends onGluconeogenesis, so it depends on VFA.Ruminants can use volatile fatty acids quickly.
VFA generated in the rumen is mainly absorbed in the form of acidic ions, about 80% of which pass through the tumor and reticulumGastric wallAbsorption, while the remaining VFAOmasum stomachAnd absorption in the stomach.Different kinds of VFAMolecular sizeDifferent, the absorption speed is different. When the rumen pH value is>7, acetic acid>propionic acid>butyric acid, while when the pH value is<7, the speed is opposite.Monogastricanimal feedMost of the glucose produced from the digestion of the sugar in the medium starch can be absorbed by the small intestine wall, and the rest can be produced by bacterial decompositionOrganic acid, including volatile fatty acids (acetic acidpropionic acidButyric acid) andlactic acid；The undigested starch and glucose in the small intestine should be transferred to the large intestine（cecum, colon) will also be decomposed by bacteria to produce volatile fatty acids and gases.throughDigestive tract absorptionInvaginousNutrientsFirst throughLiver metabolism, rear entryPosterior vena cava, viaPulmonary circulationThe propionic acid and butyric acid entering the arterial blood flow are distributed to the peripheral tissues, while the propionic acid and butyric acid entering the portal vein blood flow are almost all metabolized by the liver, and the concentration in the arterial blood flow is very low.[1]
analytical method
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principle
Gas chromatographyIt can be used to analyze the total amount of VFA and its composition.chromatographic columnThe separated distillate iscarrier gasCarry inHydrogen flame ionization detectorOfinjectorAnd mixed with hydrogen and air for combustion. The components in the sample to be measured are ionized successively asPositive and negative ionsAfter the ion current is formed in the ion chamber and collected by the collector, it is amplified into a signalRecorderrecord.The size of this signal reflects the content of each component.AndGas chromatographyThe connected microcomputer can directly process the signal. After comparing with the standard, it can directly give the concentration of each component in the sample. The concentration can be expressed in mg/Lmmol/50. Or mgCOD/L at the same time.[2]
Take several milliliters of water sample, add an equal amount of 3% formic acid solution to dilute it, and ensure its pH value is below 3. If the pH is too high, add sulfuric acid to adjust it.Diluted water sampleCODThe concentration shall be less than 1000mg/L, or the addition of 3% formic acid solution shall be increased.Recording water samplesDilution multiple。Place the above water sample inCentrifugal tube, onHigh speed micro centrifugeAfter centrifugation at 1000r/min for 5min, it can be takensupernatantInjection.[2]
chromatographic column：d2mm×2mstainless steelColumn,Fill inDomestic GDX-102 (surfaceacid treatment）Support, 60~80 mesh.Column temperature: 210 ℃, carrier gas: nitrogen,flow rate90ml/min, air flow rate: 500ml/min, temperature of vaporization chamber: 240 ℃, detection temperature: 210 ℃, and the quality of chromatographic column shall be paid attention to during selection.Vibrators andVacuum pumpInstall the support body withglass fibrePlug the column port, and then load the chromatographic columnChromatograph, proceedAging chromatographic columnWork.When not connecteddetectorUnder the condition of 4 ℃/minheating rate Heat from 60 ℃ to 200 ℃ and keep for about 4h until the baseline is stable.In each useTheThe column temperature is gradually increased from 60 ℃.[2]
Calculation of quantitative analysis results
withGas chromatographic analysisThe principle of VFA concentration is based on comparisonstandard solution The peak height and peak area of each component in and the corresponding component in the sample water sample are calculated.But modern gas chromatographs are equipped with microcomputerpeak areaconductAutomatic integrationAnd compare with the peak area of the corresponding component in the standard solutionDilution multipleCalculate the concentration of each component and print the results.If the gas chromatograph used is not equipped withIntegratorThe concentration of a component in the tested sample can be calculated by the following formula: the test result can also be mgCOD/L ormmol/L, the following table shows the VFA and mg per milligram or millimoleCODAccording to the conversion relationship of, each unit can be converted to each other.[2]
Using Rochefungus, using the mixture of glucose and propionic acid as the carbon sourceShort chainPHA。In addition, there are other types of VFABe treated asThe substrate is used for PHA production.For example, useValeric acidAnd glucose as substrate, using RocheFungal fermentation50 hours, the PHA output can reach 90.4 g/L.[3]
