Rights: University of Waikato Published 18 March 2011 Download

Dr David Stevenson, a senior scientist with Plant & Food Research, defines the term phytochemical and explains some of the actions a class of phytochemicals called polyphenols have within the plant. These range from serving as signalling molecules to boosting the plant’s defence mechanisms in warding off attack from bacterial and fungal pathogens as well as insects that use the plant as a food source.

Point of interest:
Organically grown plant crops have not been exposed to pesticides, fungicides and bactericides. Does this mean that they may contain higher levels of polyphenolic phytochemicals than conventionally grown crops?


Phytochemicals are essentially biochemicals found in plants, so all sorts of biochemicals are around, and the ones in plants we call phytochemicals. Polyphenolics are a particular class of phytochemicals.

The main role polyphenols play in plants is sort of similar to our immune system and hormone system. The signalling molecules send messages around the plant. They protect the plant from infection by bacteria and mould – probably do some antioxidant effect as well – also involved in protecting the plant from being eaten, particularly by insects. They are repellent to insects, and if an insect starts eating a plant, it will make a lot more polyphenols to try and make it stop and go away.

Bioflavenoids are one of the types of polyphenols. A lot of the coloured compounds in plants, like the purple in berries, come from compounds which we call bioflavenoids.

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