Pigment changes during processing of green table olive specialities treated with alkali and without fermentation

Abstract

Green table olive preparations including an alkaline treatment, but not preservation by natural fermentation, such as Castelvetrano-style, are gaining importance in international trade. One of the main highly valued characteristics for this product is a bright green colour, as similar as possible to the fresh fruit. Large proportions of Cu–chlorophyll complexes have been quantified in commercial products of Castelvetrano-style table olives thus in the present work the changes in the chlorophyll and carotenoid composition of olive fruits during this processing style were investigated. The high alkaline pH of the process was the most important feature governing the subsequent transformation of the chlorophyll pigments initially present in the fresh fruit. During processing, the main transformations of pigments were due to allomerization and solvolysis reactions of chlorophylls a and b, which affected the isocyclic ring of the chlorophyll structure but not the Mg atom that remained, and did not change substantially the pigment colour and, consequently, the fruit colour. No Cu–chlorophyll derivatives were detected. Then, even though the intense alkali treatment of the olives may cause such damage in the fruit cells that enables contact between the chlorophyll derivatives and the endogenous Cu of the fruit, the absence of acidic conditions during the olive processing did not lead to the previous reaction of Mg replacement by 2H, which is necessary for the following insertion of Cu. With respect to the carotenoid fraction, any noticeable change took place.