Effect of black oxidising table olive process on the cell wall polysaccharides of olive pulp (Olea europaea L. var. Negrinha do Douro)

Olive fruits of Negrinha do Douro variety were sampled after the three main steps of black oxidising processing: storage in brine, lye treatment and thermal treatment (final product). The analysis of cell wall polysaccharides showed that brine storage increased the amount of pectic polysaccharides, glucuronoxylans and cellulose in olive fruit. Those increases suggest the biosynthesis of new polysaccharides during the long storage in brine. The lye treatment had two effects: it caused degradation and loss of polysaccharides and, on the other hand, it increased their retention in the cell walls. The breakage of ester and hydrogen bonds should have been responsible for their degradation. The retention could be due to the ionisation of hydroxyl groups of cell wall polysaccharides, preventing the diffusion of negatively charged pectic polysaccharides. The thermal treatment caused mainly the loss of hemicellulosic polysaccharides and cellulose. The increased solubilisation of pectic polysaccharides observed in the final product should have been the result of dissolution of pectic polysaccharides involved in the cellular adhesion, which should result in a decreased firmness of the flesh. The application of FT-IR/multivariate analysis to the cell wall material allowed the distinction of olives before and after the lye treatment, attributed mainly to the changes in pectic polysaccharides.