Stability and antioxidant potential of purified olive mill wastewater extracts

• Published in: Food chemistry 2012-04, Vol.131 (4), p.1312-1321
• Main Authors: He, Jingren, Alister-Briggs, Michelle, Lyster, Ted de, Jones, Graham P.
• Format: Article
• Language: English
• Subjects: Antioxidant activity; Biological and medical sciences; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; Olive mill wastewaters; Pollution and sludges; Resin; Secoiridoids; Stability; Storage conditions; Total phenols
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2011.09.124

► POE rich in phenolic and oleosidic compounds prepared by amphoteric polymer resin. ► High phenol content and structural diversity of POE confer high antioxidant potential. ► Stability of POE is greatly improved comparing to original OMWW matrix and crude extract. ► Oxygen is determinant factor which influences the stability of POE at low temperature. ► Compositional changes contribute to maintenance of antioxidant potency at high temperature. A purified olive extract (POE) rich in phenolic and oleosidic compounds was prepared from olive mill wastewaters by adsorption onto an amphoteric polymer resin with the yield of 2.2% (w/v). In addition to complex and simple phenolic compounds found in the POE, the highly hydrophilic elenolic acid and DEDA (dialdehydic form of decarboxymethyl elenolic acid, a non-phenolic secoiridoids) were also present in high concentration (45%, w/w). Among the phenolic constituents, the major compounds are hydroxytyrosol and its glucoside, DEDA linked to hydroxytyrosol (Hy-DEDA), p-coumaric acid and caffeic acid, verbascoside and some flavonoids. The high content (23%, w/w in gallic acid equivalent) and structural diversity of these phenolic compounds confer superior antioxidant potential of POE with an IC50 less than 8.5μg/ml determined by DPPH assay. The stability of bioactive components during storage of the extract and changes in antioxidant properties were studied under different conditions. Determination of kinetics of degradation revealed that air/oxygen is the determinant factor which influences the stability of POE under low temperature storage conditions, while exposure to sunlight did not have significant effect on their stability. Whilst an increase in storage temperature decreased the total content of phenolic compounds (20–24% reduction) and non-phenolic secoiridoid aglycons, a high antioxidant capacity was still observed particularly in the nitrogen-protected POE samples (93–95% of the initial value). This was believed to be due to the transformation of hydroxytyrosol-containing complex phenols, especially the secoiridoid ester Hy-DEDA, into free phenolic monomer. This contributed significantly to the maintenance of a high antioxidant potency of the whole extract during storage. The high antioxidant, radical scavenging activity and stability of the extract suggest potential applications in the food and pharmaceutical industries.