Exploring the potential of natural substances from olive and grape pomace in phytoprotection

Grape pomace as by-product is approximately 20% of the harvested grapes and it is a very rich source of bioactive polyphenolic compounds, especially stilbenoids, phenolic acids and flavonoids. These polyphenols have been shown to exert beneficial effects for human health, and they are also linked to several functions in plants, such as defense against invading phytopathogens. In a similar manner, phenolic compounds in Olea europaea tissues have pharmacological properties and are natural antioxidants with both antimicrobial and health promoting effects. Oleuropein, the main phenolic glucoside found in olive fruits and leaves (up to 14% of the dry weight in unripe olives), and its aglycon, obtained from oleuropein by hydrolysis, are well-known pharmacologically active molecules with potential applications as antimicrobial agents in some fairly common olive tree diseases. Moreover, oleuropein (derived from olive tissues) and its derivatives (derived from olive mills waste waters) have a variety of biochemical roles, including anti-inflammatory and antithrombotic activities. Our aim is to exploit these natural antioxidants as phytoprotective agents against economically important pathogens on organically grown crops. Oleuropein showed high antimicrobial activity against several phytopathogenic bacteria and inhibited/delayed radial growth of some plant-pathogenic fungi. The minimal inhibitory concentration (MIC) of those compounds against Gram-positive or Gram-negative bacteria was as low as 0.02% (3.7µM). Similarly, grape polyphenols have also shown to inhibit or delay the rate of radial growth of some plant-pathogenic fungi. The phytoprotective activity of these substances of variable purity extracts was also tested in vivo on various commercial vegetables, fruits and flowers and compared to those of commercially approved phytoprotectants used in organic agriculture.

Acknowledgements: This work is funded by a research grant PEP-Crete (KR-19, co-financed by the E.U.-European Regional Development Fund, the Regional Authority of Crete and the Greek Ministry of Development-General Secretariat Research & Technology).