Interactions between substrate, fermentation end-products, buffering systems and gas production upon fermentation of different carbohydrates by mixed rumen microorganisms in vitro

Abstract

In animal nutrition, incubation of feed samples with CO2/HCO3-buffered rumen fluid is used to predict the nutritional values of the feed. During fermentation, volatile fatty acids (VFAs) are produced, which release CO2 from the buffer through their H+ ions. This indirect gas production amounted to 20.8 ml gas per mmol VFA. By incubating glucose, rice starch and cellulose, the relationship between direct and indirect gas production in relation to fermentation kinetics was studied. The total amount of gas formed was found to be dependent on the composition of the fermentation end-products formed. This could be described by: ml gas = Mv·mmol HAc + 2Mv·mmol HB + 0.87Mv·mmol Tot. VFA where HAc = acetic acid; HB = butyric acid; and Mv = molar gas volume. No clear relationship was found between the rate of fermentation and total gas production. From rice starch more total gas was produced than from glucose and cellulose, which were fermented faster and slower, respectively.