Gravimetric determination of tannins and their correlations with chemical and protein precipitation methods

Authors

  • Harinder P S Makkar,

    1. Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim, Box 700562, 7000 Stuttgart 70, Germany
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  • Michael Blümmel,

    1. Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim, Box 700562, 7000 Stuttgart 70, Germany
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  • Norbert K Borowy,

    1. Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim, Box 700562, 7000 Stuttgart 70, Germany
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  • Klaus Becker

    Corresponding author
    1. Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim, Box 700562, 7000 Stuttgart 70, Germany
    • Institute for Animal Production in the Tropics and Subtropics, University of Hohenheim, Box 700562, 7000 Stuttgart 70, Germany
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Abstract

Abstract. A method for gravimetric determination of tannins based on binding with insoluble polyvinylpyrrolidone (PVP) is presented. The gravimetric method gives the absolute amount of tannins and avoids problems of standards associated with spectrophotometric methods. The method was applied to nine browse and tree leaves. The values obtained correlate significantly with tannins determined spectrophotometrically, protein precipitation capacities and protein precipitable phenotics. This method together with other tannin assays will be useful in nutritional studies. The present study also demonstrates the different behaviour of tannic acids from different commercial sources towards PVP suggesting the presence of different moieties in tannic acids from different commercial sources and even among batches from the same source thereby affecting the results obtained using the spectrophotometric methods. Use of well-defined tannic acid as a standard in spectrophotometric methods is suggested which will allow meaningful comparison of values obtained from different laboratories.

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