Lipoxygenase distribution in coffee (Coffea arabica L.) berries.

ABSTRACT

In this paper lipoxygenase (LOX) presence was investigated in coffee berries to determine its involvement in lipid degradative metabolism of plants grown in organic and conventional cultivations. An immunochemical analysis has evidenced a ca. 80 kDa protein, cross-reacting with an anti-LOX antibody, only in the pulp fraction of berries obtained from plants of both cultivations. LOX activity in this fraction could be monitored either as conjugated diene formation or reaction products (determined by HPLC) and was mainly associated with a heavy membrane fraction (HMF, enriched in tonoplast, endoplasmic reticulum, plasma membrane, and mitochondria) and a light membrane fraction (LMF, enriched in plasma membrane and endoplasmic reticulum, with low levels of tonoplast and mitochondria). The LOX activity of LMF from berries of both cultivations showed an optimum at pH 8.0. The HMF exhibited a different activity peak in samples from conventional (pH 8.0) and organic (pH 5.5) cultures, suggesting the presence of different isoenzymes. These findings were also confirmed by variation of the ratio of 9- and 13-hydroperoxides in organic (11) and conventional cultivations (110), indicating that the organic one was subjected to an oxidative stress in the coffee pulp fraction leading to the expression of an acidic LOX. Such de novo synthesized LOX activity could be responsible for the production of secondary metabolites, which may interfere with the organoleptic profile of coffee.