Valorisation nutritive d'un grignon d'olive traité à la soude. Utilisation digestive des constituants des parois cellulaires

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Abstract
The effect of sodium hydroxide treatment on the digestibility of cell wall constituents of a screened, solvent-extracted olive cake was assessed in the adult sheep. Solutions were sprayed to reach 0, 5, 7.5 and 10 g NaOH/100 g by-product. The effect of sodium hydroxide treatment on the nutritive value of olive cake and the accuracy of some chemical and biological laboratory methods for estimating the nutritive value of this by-product have been studied in a previous paper (Aguilera and Molina, 1986). Soda treatment significantly improved (P < 0.001) NDF, ADF, ADL and cellulose apparent digestibilities (Table 2). On the contrary, it did not increase significantly the digestibility of the hemicellulose fraction. This effect on cell wall digestibility accounts for the increase in the nutritive value of the olive cake following the NaOH treatment (Aguilera and Molina, 1986). Absorbance at 280 nm of solutions obtained by extraction with distilled water of the olive cake after the soda treatment (Graphic 1) proved to be an excellent laboratory method to predict both the digestibility of cell wall components and the digestibility of the organic matter and the energy value of the by-product (Table 3). RSD values from this method are lower than those derived from chemical and biological laboratory methods (Aguilera and Molina, 1986). In conclusion, the improvement produced by the soda treatment on the digestibility of cell wall constituents is important. However, the treated by-product has still a poor energy value as the availability of the cell wall components remains rather low and this fraction accounts for most part of the organic matter in the olive cake.