Food Research International 52 (2013) 167–177 Contents lists available at SciVerse ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres Review Phytoalexins from the Poaceae: Biosynthesis, function and prospects in food preservation Chukwunonso E.C.C. Ejike a,b, Min Gong c, Chibuike C. Udenigwe c,⁎ a Department of Food Science, University of Guelph, Ontario, N1G 2W1, Canada b Department of Biochemistry, College of Natural and Applied Sciences, Michael Okpara University of Agriculture, Umudike, PMB 7267, Umuahia, Abia State, Nigeria c Health and Bio-products Research Laboratory, Department of Environmental Sciences, Faculty of Agriculture, Dalhousie University, Truro, Nova Scotia, B2N 5E3, Canada article info abstract Article history: Phytoalexins are compounds synthesized by plants in response to extrinsic stress such as microbial attack and Received 15 January 2013 physical injury. Some members of the Poaceae, including cereal crops rice, maize and sorghum, are known to Accepted 9 March 2013 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 Keywords: genes. Phytoalexins identified in the cereal food Poaceae include the momilactones, oryzalexins, phytocassanes Phytoalexin and sakuranetin from rice; the kauralexins and zealexins from maize; and the 3-deoxyanthocyanidins from sor- Poaceae Food preservation ghum. These phytoalexins are known to exhibit considerable antimicrobial activities against a wide array of Antimicrobial pathogenic fungi and bacteria. Despite their prospects for use as naturally derived antimicrobial agents, there Elicitor 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. © 2013 Elsevier Ltd. All rights reserved. Contents 1. Introduction ............................................................. 168 2. Promoting food security through food preservation ........................................... 168 3. Brief history of phytoalexins ...................................................... 168 4. Phytoalexins and the Poaceae ..................................................... 169 4.1. Rice .............................................................. 169 4.2. Maize ............................................................. 169 4.3. Wheat ............................................................. 169 4.4. Barley ............................................................. 170 4.5. Sorghum ............................................................ 171 5. Chemistry and antimicrobial properties of phytoalexins produced by the Poaceae . ............................ 171 5.1. Terpenoid phytoalexins ..................................................... 171 5.1.1. Diterpenoid phytoalexins ................................................ 171 5.1.2. Sesquiterpenoid phytoalexins .............................................. 172 5.2. Flavonoid phytoalexins ..................................................... 173 5.2.1. Sakuranetin ...................................................... 173 5.2.2. 3-Deoxyanthocyanidins ................................................. 173 6. Biosynthesis of phytoalexins produced by the Poaceae .......................................... 173 6.1. Terpenoid phytoalexins ..................................................... 173 6.2. Flavonoid phytoalexins ..................................................... 174 6.2.1. Sakuranetin ...................................................... 174 6.2.2. 3-Deoxyanthocyanidins ................................................. 174 ⁎ Corresponding author. Tel.: +1 902 843 6625; fax: +1 902 843 1404. E-mail address: [email protected] (C.C. Udenigwe). 0963-9969/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodres.2013.03.012 168 C.E.C.C. Ejike et al. / Food Research International 52 (2013) 167–177 7. ProspectsofphytoalexinsfromthePoaceaeinfoodpreservation...................................... 174 8. Conclusion and future direction ..................................................... 175 Acknowledgment .............................................................. 175 References ................................................................. 175 1. Introduction One neglected component of ensuring food security is reducing losses and wastages. Food losses refer to the reduction in the quantity The challenge of food security remains a major global obstacle facing of edible food at any point in the food supply chain, that is, the produc- mankind. Although food production has increased in the last few de- tion, postharvest and processing stages. Losses occurring at the retail cades, the progress made in improving the quantity of food produced and consumption stages – end of the food supply chain – are rather annually may not ensure global food security in the future with enor- called “food waste” (Julian & Barthel, 2010). Food wastages are found mous food losses and wastages (Gustavsson, Cederberg, Sonesson, more in developed countries while food spoilage occurs more in devel- van Otterdijk, & Meybeck, 2011). As part of current initiatives to oping countries. It is estimated that about 33% of the food produced enhance food security, proper preservation methods are required to globally (about 1.3 billion tonnes per year) is wasted before or after it ensure that the best food quality and shelf-life are attained. Recently, gets to the final consumer (FAO, 2012a; Gustavsson et al., 2011). It is there has been a drive towards the use of “natural” food preservatives, further projected that halving the amount of food wasted globally especially as synthetic preservatives raise health-related concerns, and (assuming 30% is currently wasted) would provide 25% of current pro- as properties of foods other than their nutritional and sensory attributes duction by 2050 thereby enhancing future food security (Government are recognized (Corbo et al., 2009). In this direction, plant-derived Office for Science, London, 2011). Reducing food losses and wastages, compounds with antimicrobial activity are now increasingly explored in order to guarantee food security requires among other things, for use in the preservation and enhancement of food quality. In light efficient processing and preservation techniques that guarantee food of these developments, there is a need to discover sustainable means quality and improve shelf-life. Considering that microorganisms and of producing structurally diverse natural antimicrobial agents, and to enzymes are responsible for a large proportion of food spoilage and overcome microbial resistance that can possibly be encountered with losses (Turgis, Vu, Dupont, & Lacroix, 2012), the development of safe the use of specific antimicrobial preservatives. and natural antimicrobial food additives and enzyme inhibitors as Phytoalexins have been studied for more than a century, and there components of systems that can enhance the effectiveness of preserva- exists a large body of knowledge on these inducible plant defense com- tion while maintaining product quality and safety would help elongate pounds, which are mostly antimicrobial. Plants in the family Poaceae shelf-life and improve food security (see Tajkarimi, Ibrahim, & Cliver, are about the most geographically widespread plants on earth, and 2010 for a detailed review on food-derived antimicrobial agents). they have been reported to produce a variety of structurally diverse Therefore, we foresee a role for stress-induced phytoalexins from the phytoalexins (Peters, 2006). Moreover, progress has been made in cereal food Poaceae as natural antimicrobial agents for food preserva- genetically modifying plants to make them produce, or enhance their tion (Fig. 1) due to their structural diversity, abundance and wide global production of, certain desirable phytoalexins (Großkinsky, van der distribution of their food sources. Graff, & Roitsch, 2012). However, there is scarcity of literature informa- tion on the potential use of phytoalexins as antimicrobial agents in the 3. Brief history of phytoalexins food system. This paper reviews the current state of knowledge on the chemistry and biosynthesis of phytoalexins from the five most Phytoalexins are a diverse group of low molecular weight secondary important cereals produced globally – rice, maize, wheat, barley and metabolites that exhibit antimicrobial activity, and are momentarily sorghum – and draws attention to their potential use and prospects as generated by either endogenous or exogenous signal molecules (biotic natural antimicrobial food preservatives. and abiotic stressors) called elicitors. They are an important part of the plant's defense gamut (Pedras, Yaya, & Glawischnig, 2011; Schmelz 2. Promoting food security through food preservation et al., 2011) and their antimicrobial effect is targeted to a variety of plant pathogens. The French botanist Noel Bernard, working more Food security is defined as a “situation that