Phytoalexins from the Poaceae: Biosynthesis, function and prospects in food preservation

Phytoalexins are compounds synthesized by plants in response to extrinsic stress such as microbial attack and physical injury. Some members of the Poaceae, including cereal crops rice, maize and sorghum, are known to produce substantial amounts of structurally diverse groups of phytoalexins. However, no phytoalexin has been identified in other cereals such as wheat and barley although they possess certain phytoalexin biosynthetic genes. Phytoalexins identified in the cereal food Poaceae include the momilactones, oryzalexins, phytocassanes and sakuranetin from rice; the kauralexins and zealexins from maize; and the 3-deoxyanthocyanidins from sorghum. These phytoalexins are known to exhibit considerable antimicrobial activities against a wide array of pathogenic fungi and bacteria. Despite their prospects for use as naturally derived antimicrobial agents, there is scarcity of information on the application of these inducible compounds in the food system. Since food wastage due to spoilage microorganisms constitutes a challenge in global food security, these phytoalexins can potentially be utilized as sustainable natural antimicrobial food preservatives considering the abundance of their sources. This paper reviews the chemistry, biosynthesis and antimicrobial activities of phytoalexins from the cereal food Poaceae, and highlights their potential application in food preservation.