Characterization of a 13-lipoxygenase from virgin olive oil and oil bodies of olive endosperms

Abstract

Olive oil is one of the oldest known vegetable oils, and it is almost unique in that it can be consumed without any refining treatment. One of its most important quality problems is oxidative rancidity due to the oxygenation of polyenoic fatty acids and formation of compounds that derive from these fatty acid hydroperoxides. Beside autoxidation, lipoxygenases (LOXs) were suggested to be involved in this process. Here we show, that approximately 1.6% of all linoleic acid (LA) molecules within olive oil samples had been converted into LOX‐derived (13S,9Z,11E)‐13‐hydroperoxy‐9,11‐octadecadienoic acid (13‐HPODE) as determined by 1H NMR‐ and HPLC analysis. LOX activity tests indicated the occurrence of an active 13‐LOX exhibiting a pH optimum between pH 5.5 and 6.0. Furthermore, this enzyme preferentially metabolized free fatty acids. In order to elucidate the origin of this LOX, we analyzed olive endosperms for LOX forms. Chromatography of total protein extracts of the tissue showed LOX activity almost exclusively associated with a high molecular mass fraction. Light microscopic inspection, as well as the calculated phosphate, neutral lipid, and protein content of this fraction, suggested that this fraction may contain oil bodies and that LOX activity was associated with their membrane. This LOX activity had a pH optimum of 6.0. Activity assays at various temperatures indicated a significant catalytic efficiency of the enzyme up to 55°C. HPLC analysis of LA oxygenation products within the lipid fraction and of activity tests of isolated oil bodies showed that the LOX present in mature olive endosperm oil bodies was, as the enzyme from olive oil, a linoleate 13‐LOX preferentially active on free LA. We suggest, that this oil body LOX from olive endosperm, is the one detected originally in olive oil and may survive at least in part olive oil production.

Mechanical Strategies to Increase Nutritional and Sensory Quality of Virgin Olive Oil by Modulating the Endogenous Enzyme Activities

“…LOX activity was measured in both olive pulp membrane fractions by Salas and others () and callus cultures by Williams and others (). Specifically, LOX activity was detected in particulate fractions of enzyme extracts from olive pulp (Salas and others ) and also in oil bodies extracted from olive endosperms (Georgalaki and others ) and pulp (Lorenzi and others ).…”

Evaluation of Olive Fruit Lipoxygenase Extraction Protocols on 9- and 13-Z,E-HPODE Formation

“…Moreover, hydrophobicity of LOX may cause protein aggregation, making the extraction process even more demanding [7]. Nonetheless, several research groups have successfully isolated olive LOX utilizing various modified procedures, independently described by Georgalaki and Donaire [15,16]. The purpose of this study was to determine the extent to which those extraction procedures affect enzyme activity.…”

The Malaxation Process

“…Polyphenoloxidase (PPO) and peroxidase (POD) can oxidize phenolic compounds (i.e., secoiridoids), resulting in reduced phenolic concentration of the oil. Potential effects on product quality characteristics include a decrease in the 'bitter' and 'pungent' sensory attributes, oxidative stability and a reduction in the nutritional value of virgin olive oil (Georgalaki et al, 1998;Ranalli et al, 2001).…”