Fermentation of flavonols by rumen organisms

Abstract

Forage plant phenolics with no tanning activity, although usually of low mammalian toxicity, are generally regarded as antinutrients (Harborne 1991). However some are degraded in the ruminant digestive tract and the “A” ring of flavonoids (Figure 1), being derived from acetate in biosynthesis, may in principle yield acetate. This has been shown to occur in vitro on prolonged incubation of quercetin with Eubacterium oxidoreductans (Krumholz and Bryant 1986). Here we investigate the fate of 3 flavonoids when incubated with a mixed rumen inoculum under conditions that simulate rumen fermentation. This experiment employed an in vitro gas pressure system in use for determining the rate of fermentation of fibrous substrates (Pell and Schofield 1993), in which we replaced the plant material with the pure compound being tested (sample size 25 mg instead of 100 mg). Rumen fluid came from a sheep on a Rhodes grass-luceme diet. Compounds tested were quercetin, it.s 3-rhamnoglucoside, rutin (Figure l), and catechin which differs from quercetin only in the oxidation of the “C” ring. Gas pressures were monitored during.