Controlling the formation of indole and skatole in in vitro rumen fermentations using condensed tannin |
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| Authors: | Nicola M Schreurs Michael H Tavendale Geoffrey A Lane Tom N Barry Nicolas López‐Villalobos Warren C McNabb |
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| Affiliation: | 1. Food Metabolism & Microbiology Section, Food and Health Group, Grasslands Research Centre, AgResearch Ltd, Private Bag 11008, Palmerston North, New Zealand;2. Institute of Veterinary, Animal & Biomedical Science, Massey University, Palmerston North, New Zealand;3. Forage Biotechnology Section, Grasslands Research Centre, AgResearch Ltd, Private Bag 11008, Palmerston North, New Zealand |
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| Abstract: | Indole and skatole are formed in the rumen from the fermentation of tryptophan and have been correlated to the presence of undesirable pastoral flavours in meat from grazing ruminants. A series of four in vitro rumen fermentation experiments was carried out to determine the effectiveness of condensed tannin (CT) for reducing the formation of indole and skatole. Experiment 1 utilised fresh white clover (WC; Trifolium repens) in ratios with the CT‐containing forage Lotus pedunculatus (LP; 97 g CT kg?1 dry matter (DM)). Increasing the ratio of LP to WC decreased the formation of indole and skatole. Experiments 2 and 3 used extracts of CT from LP and grape seed added to incubations of fresh non‐CT‐containing WC or perennial ryegrass (PRG; Lolium perenne). Including the CT extracts in incubations at 40 and 80 g kg?1 DM was more effective at reducing indole and skatole formation than lower concentrations of CT extract (P < 0.05). Including fresh LP in ratios with WC gave a linear decrease in indole and skatole concentration (indicating dilution), while including a CT extract in the incubations gave an exponential decrease in indole and skatole concentration (suggesting binding). Experiment 4 elucidated the mechanisms behind the action of CT by delayed addition of tryptophan and polyethylene glycol (PEG) to incubations of LP. Rumen microbes that were exposed to CT of LP in planta for up to 6 h and then provided with tryptophan were still able to convert tryptophan to indole and skatole. Adding PEG to incubations of LP after 6 h inhibited the activity of plant CT and increased the availability of substrate for indole and skatole formation. These studies have shown that a higher concentration of CT is more efficient for reducing indole and skatole formation and that CT contained within plants acts differently in in vitro rumen fermentations than additions of extracted CT. Under the conditions of these experiments, there was no evidence that CT contained in LP affected the protein present in WC in a mixed fermentation. Copyright © 2007 Society of Chemical Industry |
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| Keywords: | indole skatole in vitro pastoral flavour condensed tannins forage white clover (Trifolium repens) Lotus pedunculatus perennial ryegrass (Lolium perenne) |
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