Production in Large Quantities of Highly Purified Hydroxytyrosol from Liquid−Solid Waste of Two-Phase Olive Oil Processing or “Alperujo”

Abstract

The effect of hydrothermal treatment of two-phase olive waste (alperujo) on the solubilization of hydroxytyrosol was studied. Different conditions of saturated steam were assayed. A high amount of hydroxytyrosol was solubilized and increased with increasing steaming temperature and time, reaching 1.4−1.7 g/100 g of dry alperujo. The effect of acidic (H₂SO₄) and basic (NaOH) catalysts was also evaluated. Acid-catalyzed treatment was more effective at milder conditions, whereas the alkali-catalyzed conditions were not very suitable. In the present study, the extracted hydroxytyrosol was purified by means of a new, simple, and inexpensive chromatographic system, under international patent application (PCT/ES02/00058). From 1000 kg of alperujo, with 70% humidity, can be obtained ∼4.5−5 kg of hydroxytyrosol. After a purification process, at least 3 kg of hydroxytyrosol, at 90−95% purity, would be obtained. The purified compound was identified by HPLC/UV and ¹H and ¹³C NMR analyses, and its antioxidant activity was tested on refined olive oil without antioxidants by Rancimat method. The oxidative stability of refined olive oil was increased by a factor of 1.71 in the presence of 100 ppm of hydroxytyrosol. Keywords: Liquid−solid two-phase olive waste (alperujo); hydrothermal treatments; hydroxytyrosol; HPLC analysis; antioxidant; chromatography; spectroscopy