Melanin and humic acid-like polymer complex from olive mill waste waters. Part I. Isolation and characterization

Abstract

A water soluble humic acid and melanin-like polymer complex (OMWW–ASP) was isolated from olive mill waste waters (OMWW) by ammonium sulfate fractionation to be used as natural additive in food preparations. The dark polymer complex was further characterized by a variety of biochemical, physicochemical and spectroscopic techniques. OMWW–ASP is composed mainly of proteins associated with polyphenols and carbohydrates and the distribution of its relative molecular size was determined between about 5 and 190kDa. SDS–PAGE shows the presence of a well separated protein band of 21.3kDa and a low molecular weight peptide. The OMWW–ASP complex exhibits a monotonically increasing UV–Vis absorption spectrum and it contains stable radicals. Antioxidant activity measurements reveal the ability of the OMWW protein fraction to scavenge both the cationic 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) radical, as well as the stable nitroxide free radical 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL).