Purification of ferulic acid by adsorption after enzymic release from a sugar-beet pulp extract

An aqueous sugar-beet pulp extract obtained by pressure-cooking and mainly composed of pectic fragments, was treated with a pectinolytic preparation. A strong, but limited depolymerization occurred fastly, while feruloyl-esterase activities appeared more gradually, pointing to some deficiencies of the enzymic mix. The solubility of ferulic acid in the sugar-rich, acidic hydrolysate proved stable, and no crystallization could be triggered in this complex medium. Comparative batch tests were carried out with preselected commercially-available adsorbents: activated carbons, polystyrenic divinylbenzene-crosslinked resins, and polyvinylpolypyrrolidone (PVPP). In each case, the ferulic acid uptake is lower at pH values above 4.5, the pKa determined for its carboxylic group. The natural acidity of the hydrolysate, pH 3.4, was chosen as the optimum. The chemically-activated carbon (SA1817) has the highest affinity for ferulic acid, while Amberlite XAD-16 performs best among the polystyrenic resins. PVPP also offers an appreciable adsorption efficiency. Selectivity is ensured, since only the charcoal removes a slight amount of galacturonic acid, which is released on rising the pH to 4. Alkaline dissociation and ethanolic extraction were investigated as desorption strategies, and ethanol was kept as the most suitable common eluent. Dynamic column studies allowed to estimate the maximum specific capacity at about 22, 12 and 8% (w:w ferulic acid/adsorbent) for the chemical granular activated carbon (GAG), XAD-16 and PVPP, respectively. Ferulic acid is quantitatively recovered after ethanolic elution of the three selected adsorbents, and the best purity is achieved with PVPP, followed by GAG. (C) 1997 Elsevier Science B.V.