Ciência Rural (Sep 1998)
Caracterização de método laboratorial específico para volumosos tratados com álcalis Characterization of a specific laboratorial method for alkali-treated roughages
Abstract
O método específico para volumosos tratados com álcalis, descrito por LAU & VAN SOEST (1981), foi avaliado, com palha de trigo, para caracterizar seus atributos, utilizando-se a digestibilidade in vitro (DIVMO) como método referência. As estimativas de compostos fenólicos dissociados pelo tratamento com álcali (ABS-REF), de grupos tituláveis (GT) e de lignina residual associada à parede celular de materiais tratados (ABS-TIT) apresentaram, nesta ordem, repetibilidade decrescente. A precisão das medidas de GT e de ABS-TIT é mais baixa para palha tratada (NaOH 4%) em relação à não tratada, e resultados obtidos em diferentes corridas laboratoriais podem diferir significativamente. As estimativas da exatidão das medidas de ABS-REF e GT, dada pela correlação entre seus valores e os de DIVMO obtidos com palha tratada com 0 a 4% de NaOH, foram altas, rABS-REF = 0,96 (PThe specific method for alkali-treated roughages described by LAU & VAN SOEST (1981) was evaluated, using wheat straw and in vitro digestibility (DIVMO) as reference method, aiming the characterization of its attributes. The estimated phenolic compounds dissociated during the alkali treatment (ABS-REF), titrable groups (GT) and residual lignin that remained in the cell wall after chemical treatment (ABS-TIT) showed, in this sequence, decreasing repeatability. The precision of the GT and ABS-TIT measurements with treated straw (NaOH 4%) were lower than with untreated straw, and results obtained in different batches can exhibit significant differences. The accuracy estimates of ABS-REF and GT measurements, obtained by correlation analysis between the values of 0 to 4 % NaOH treated straw and DIVMO, were high, rABS-REF = 0.96 (P<0.01) and rGT = -0.83 (P<0.01), and were reduced when the values obtained with urea treated straw was introduced in the analysis. The ABS-TIT values showed high imprecision and no significant relationship was found between them and DIVMO. GT measurements can be used to screen straws before alkali-treatments and, together with ABS-REF measurements, to predict straw-treated digestibility.
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