Use of manganese in black olive processing

Abstract

Colour is the most important organoleptical characteristic among the main quality attributes of black olives. Olives can be darkened either by natural or artificial methods. The artificial process of producing ripe black olives consists of successive treatments of fruits with a sodium hydroxide solution. In this operation olives darken progressively due to the oxidation of ortho-diphenols, hydroxytyrosol and caffeic acid. Various metal cations may catalyze the darkening reaction, in particular manganese (Mn) ions, being recognized as safe to use, are favourable in accelerating the reaction. In order to obtain a darker skin colour in the final product with minimal residue content, manganese salts are used in various steps of ripe olive processing.