Colonic absorption of inorganic ions and volatile fatty acids in the rabbit

Net fluxes of water, Na+, K+, Cl-, HCO3- and volatile fatty acids (VFA) were investigated in three different segments of rabbit colon. Two opposite phenomena occurred: secretion of water and inorganic ions in the oral part of the colon and absorption in the remaining colon; VFA were always absorbed. The movement of cations was closely correlated with those of VFA and Cl-. Results are consistent with the presence of exchange: Na+/H+, K+/H+, in the colon brush border membrane. In fact net absorption of cations and VFA seems linked to the availability of protons. In the absence of net cation transport an additional source of protons may be provided by hydration of luminal CO2. So VFA could enter mucosa by passive diffusion as the undissociated acids.     

Interconversions and production of volatile fatty acids in the sheep rumen

1. Sheep fed at a constant rate were infused intraruminally with [1-(14)C]-acetate, -propionate or -butyrate during 5hr. periods. 2. Volatile fatty acids were estimated in the rumen contents and steady-state conditions were obtained. 3. Of the butyric acid carbon 60% was in equilibrium with 20% of the acetic acid carbon, and 2-3g.atoms of carbon were interconverted/day. 4. Little interconversion took place between propionic acid, acetic acid or butyric acid. 5. The net production rates for acetic acid, propionic acid and butyric acid were 3.7, 1.0 and 0.7moles/day respectively. 6. The production of volatile fatty acids accounted for 80% of the animal's energy expenditure.     

Betaine increases net portal absorption of volatile fatty acids in Iberian pigs

Betaine is an osmolyte with the potential to increase volatile fatty acids (VFAs) production and hence improve intestinal health.The present study investigated how betaine affects portal and arterial concentrations and net portal absorption (NPA) of VFA in growing Iberian pigs. Eight 30 kg BW Iberian growing barrows with indwelling catheters in portal vein, ileal vein and carotid artery were randomly assigned to a control diet or a diet supplemented with 0.5% betaine. Para-aminohippuric acid was infused into the ileal vein as a marker to determine portal blood flow using the dilution method. Blood samples were simultaneously taken from the carotid artery and portal vein at −60, 60, 120, 180, 240, 300 and 360 min after feeding 1 200 g of the diet. The NPA of VFA (acetate, propionate, butyrate, valerate, isobutyrate and caproate) was determined by multiplying the porto-arterial plasma concentration differences by portal plasma flow. Betaine increased NPA of acetate (1.44 fold; P < 0.001) and total VFA (0.55 fold; P < 0.001) while decreased NPA of propionate (−0.38 fold; P < 0.05) and valerate (−1.46 fold; P < 0.05) compared with control pigs. Estimated heat production potentially derived from NPA of VFA accounted for 0.20–0.27 of metabolizable energy for maintenance. Acetate and propionate accounted for most of the total VFA estimated heat production (0.83–0.89). Regarding bacterial communities, betaine apparently did not change the DNA abundance of fecal total bacteria, Lactobacillus, Bifidobacterium, Enterobacteriaceae, Bacteroides and the Clostridium clusters I, IV and XIV. In conclusion, betaine increased portal appearance and NPA of VFA, contributing to cover maintenance energy requirements.     

Microbial production of volatile fatty acids: current status and future perspectives

Volatile fatty acids (VFAs) are used as building blocks to synthesize a wide range of commercially-important chemicals. Microbially produced VFAs (acetic acid, propionic acid, butyric acid, isobutyric acid, and isovaleric acid) can be considered as a replacement for petroleum-based VFAs due to their renewability, degradability, and sustainability. The main objective of this review is to summarize research and development of VFA production methods via microbial routes, their downstream processes, current applications, and main challenges. Various fermentation processes have been developed to produce of VFAs starting from commercially-available sugars and other raw materials such as lignocellulose, whey, and waste sludge. Only few microbes have been explored for their potential to produce VFAs, and very little genomic information data is available at the present time. There is a need to use metabolic engineering, systematic biology, evolutionary engineering, and bioinformatics to discover VFA biosynthesis routes since the pathways for isobutyric acid and isovaleric acids are still not well understood.     

Concentrations of volatile fatty acids and acetate production rates in the forestomachs of grazing camels

1. Concentration profiles of volatile fatty acids (VFA), fluid volumes and turnover rates, and acetate production rates were measured in two different seasons in the forestomachs of four fistulated dromedary camels grazing in the Kenyan thornbush savannah. 2. VFA profiles and average concentrations were similar under both feeding conditions but, due to a smaller fluid turnover, VFA outflow to lower gastric sections in the dry season was reduced by almost 50%. 3. The mean acetate production rate fell from 2234 mmol/hr in the green season to 816 mmol/hr in the dry season, i.e. by approximately 64%.     

Hydrogen and volatile fatty acids production from marine macroalgae by anaerobic fermentation

Hydrogen and volatile fatty acids (VFAs) were coproduced from marine macroalgae by anaerobic fermentation using a microbial community. The hydrogen and VFAs production were characterized based on inoculum heat-treatment, methanogen inhibitor addition, operating temperature, and in-situ extraction of VFAs. Maximum hydrogen of 179 mL/g-VS and VFAs concentration of 9.8 g/L were produced from 35 g/L of S. japonica within 5 days of anaerobic fermentation. Hydrogen and VFAs yields were well-correlated with carbohydrate content of substrate. Inoculum heat-treatment significantly improved hydrogen production while the VFAs productivity was affected adversely. The addition of methanogen inhibitors also enhanced the hydrogen production, but the effect on VFAs production was dependent on the type of inhibitor used. Low temperature (25°C) was found to be favorable for high hydrogen and VFAs yield, while high temperature (40°C) and programmed-temperature (35 ~ 45°C) were more favorable for hydrogen and VFAs productivity. Clostridium sp. content was found to be the most abundant at 25°C. An extractive fermentation with anion-exchange resin was tested to recover the VFAs and to control the pH during the anaerobic fermentation.     

Effect of the nature of carbohydrates in pig diets on the intestinal absorption of volatile fatty acids

The appearance of nutrients (amino nitrogen and reducing sugars) and microbial metabolites (volatile fatty acids, VFA) was measured quantitatively in five pigs. After ingestion of a semi-synthetic diet (RFL) containing 22% lucerne meal (6% crude fibre), the absorption of reducing sugars (RS) in the small intestine was high (97.8%) and that of VFA low (880 +/- mmoles/24 hrs.). Ingestion of a semi-synthetic diet (RLa) containing 22% lactose and 6% purified cellulose led to lower absorption of RS (85.2%) and a higher absorption of VFA (1,180 +/- mmoles/24 hrs).     

Effect of volatile fatty acids mixtures on the simultaneous photofermentative production of hydrogen and polyhydroxybutyrate

Bioprocess and Biosystems Engineering - Purple non-sulfur bacteria generate hydrogen and polyhydroxybutyrate (PHB) as a mechanism for disposing of reducing equivalents generated during substrate...     

Influence of purified cellulose level in the diet of pigs on intestinal absorption of volatile fatty acids

Nutrient and volatile fatty acid (VFA) absorption to portal blood was measured twice at 7 days interval in five pigs fed a semi-synthetic diet containing 6 (R6) or 16% (R16) purified cellulose for 21 or 7 days. The daily absorption (24 hrs.) of VFA in the large intestine which was larger (NS) when the cellulose level rose, increased significantly (P less than 0.05) with increasing length of adaptation (21 to 28 d.) to the diet whatever the cellulose level. The supplementary daily supply of energy in the form of VFA after increase of the cellulose level did not compensate for the corresponding deficit of absorption of reducing sugars and crude protein in the small intestine.