EFFECT OF STEAMING AND AUTOCLAVING OAK (QUERCUS-INCANA) LEAVES ON LEVELS OF TANNINS, FIBER AND LIGNIN AND INSACCO DRY-MATTER DIGESTIBILITY

Oak (Quercus incana, Roxb) leaves were subjected to steaming or autoclaving (1.05 kg cm-2) for 10 and 20 min. For the fresh whole leaves, both steaming and autoclaving did not decrease substantially the levels of total phenols (TP), condensed tannins (CT), ellagitannins (ET) and protein precipitation capacity (PPC). At a 1:2 (w/v) ratio of dry ground leaves and water, steaming reduced the TP, CT, ET and PPC by about 10, 29, 30 and 25%, respectively, whereas these values were 27, 54, 64 and 53%, respectively, on autoclaving for 10 min. Increase of treatment time did not increase the reduction in tannin. The reduction of tannin levels decreased on increasing the water content from 1:2 to 1:3 (w/v of leaves to water). The in-sacco dry matter digestibility increased marginally on steaming or autoclaving. Various fibre fractions and lignin increased following the heat treatments. Proanthocyanidins (PAs) per g neutral-detergent fibre or acid-detergent fibre (NDF, ADF) decreased on autoclaving. The PAs in NDF per g leaves was almost similar whereas PAs in ADF per g leaves decreased substantially following autoclaving, suggesting that heat treatment increased the solubility of PAs in an acid-detergent solution. This can introduce errors in the values obtained for fibre and lignin using detergent system of analysis. The extractability of PAs in 50% aqueous methanol also decreased following autoclaving. The data obtained suggested that this decrease in extractability is probably due to binding of PAs to proteins on heat treatment.