Distribution of condensed tannins (proanthocyanidins) in various fibre fractions in young and mature leaves of some oak species

The distribution of proanthocyanidins (PAs), using HCl-butanol reagent, was studied in various fractions in young and mature leaves of five oak species, Quercus incana, Quercus semecarpifolia, Quercus serrata, Quercus ilex and Quercus glauca. In leaves of all the oak species studied, PAs expressed as A550 nm g−1 whole leaf, neutral detergent fibre (NDF) or acid detergent fibre (ADF) were higher in mature leaves. When the PAs were expressed as a percentage of the total PAs, the PAs in NDF were lower in mature leaves except for Q. ilex, and in ADF were lower in young leaves. Significant proportions of total PAs were present in NDF and ADF; the values ranged from ∼ 7 to 28% in NDF and from 3 to 21% in ADF. Similarly, PAs which could not be extracted using 50% aqueous methanol varied from 10 to 55% of the total PAs. These observations suggest that there is a need to recognise the importance of these tannins as well as those which are extractable. The PAs in both NDF and ADF had a significantly positive correlation with total and unextracted PAs and NDF, and with ADF, hemicellulose, cellulose and lignin their correlations were positive but not significant. The results are discussed in relation to maturity of the leaves and their likely contribution towards producing artefacts or errors when using the detergent system of feed analysis.