Table olives as a source of natural antimicrobials

Olives, olive oil and olive leaf extracts have been recognized with medicinal benefits and food preservation properties for centuries because of their content of antimicrobial compounds. Researchers first attributed this activity to the glucoside oleuropein, which is the major phenolic compound in olive fruits. However, we have recently demonstrated that in olive products the main antimicrobials are the dialdehydic form of decarboxymethyl elenolic acid free or linked to hydroxytyrosol and tyrosol. In this work, the presence of these substances has been analyzed in the solutions used to process table olives. They were not detected in the washing waters and brine of the Spanish-style green olive processing and, by contrast, a significant amount was found in the preservation solutions of the black ripe olive processing. These antimicrobials increased in the preservation solutions during the first 4–6 months of fermentation up to a concentration of 2–5 mM and declined thereafter because of their acid hydrolysis during the summer season. The analyses were carried out in industrial tanks containing 10000kg of fruits and 5000 liters of an acidified solution with acetic acid. It has been shown that both the dialdehydic form of decarboxymethyl elenolic acid free or linked to hydroxytyrosol exert a strong antibacterial activity against food and plant pathogens and these table olive solutions could therefore be used to treat plant diseases.