In order to maintain product quality and protect consumers, food producers must control microbial contamination that could cause spoilage or foodborne illness. However, current expectations from consumers mean that natural is better for acceptance in the marketplace. For this reason, food industry researchers are looking at plant antimicrobials as ‘natural’ tools to control bacteria, viruses, fungi and other microbes in products1.
Although chemical additives have a proven and reliable record as antimicrobials and food preservatives, consumer preference is for reducing their use in food. Indeed, Holvoet et al. (2015) noted recently that even though levels of foodborne infections are rising, especially from fresh and ready-to-eat foodstuffs, the European Union (EU) only has regulations governing chemical residue limits in foods but when it comes to microbial load it is unclear how the regulations are to be applied to these food types2. Partly as an acknowledgment of consumer preference but also as a measure to avoid resistance issues, food producers are now beginning to take note of naturally occurring antimicrobials found in plants.
What are plant antimicrobials?
Just as humans and animals need to fight infection and infestation, so do plants. Released as peptides (PAMPs) or phytochemicals, plant antimicrobials act on pathogens and certain toxins to prevent disease. Phytochemicals, including essential oils, flavones and flavonoids, and quinones, are more familiar to the food industry and consumers, having have been used to combat bacterial spoilage and eradicate pathogens in meats and other foodstuffs3. PAMPs are less widely known; however, research into activity of molecules such as defensins, thionins and snakins shows their potential as antimicrobials in food production.
How do they work?
The majority of plant antimicrobials seem to act by disrupting microbial cell membranes. There is some evidence that they may be more effective in Gram-positive rather than Gram-negative bacteria, but this varies according to food matrix, pathogen and plant antimicrobial. Researchers have also found in vitro activity against viruses, through envelope effects and by interfering with pathogen adsorption during the host cell entry process. PAMPs and phytochemicals also effectively disrupt protozoal and fungal cell membranes, in addition to inhibiting intracellular factors necessary for function and survival. Despite having such a profound effect on plant pathogens, it is interesting to note that beneficial commensal bacteria populations in the host are usually unaffected by plant antimicrobials.
Why use them?
As mentioned previously, the current consumer preference for natural products that are free from preservatives presents a problem to food producers in terms of preventing spoilage and guarding against foodborne pathogen contamination. Not only are plant antimicrobials perceived as natural, they also show promising results in eradicating or controlling pathogens and food spoilage organisms within food matrices. Furthermore, they also seem to avoid development of resistance—an issue that plagues common antimicrobials derived from fungi and bacteria. This is partly due to the novel source for these potential antimicrobials and also due to their action as nonspecific host defenses against a wide range of microorganisms.
Globally, plants have a long history of use in medicine and food preparation. As researchers look into the key constituents of plant antimicrobials and characterize their activity, it makes good sense for the food industry to examine how to exploit these natural compounds effectively for consumer acceptance and product safety.
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1. Hintz, T. et al. (2015) “The Use of Plant Antimicrobial Compounds for Food Preservation“, BioMed Research International 2015, Article ID 246264 http://dx.doi.org/10.1155/2015/246264
2. Holvoet, K. et al. (2015) “Agricultural and Management Practices and Bacterial Contamination in Greenhouse versus Open Field Lettuce Production“, International Journal of Environmental Research and Public Health 12 (pp.32-63) doi:10.3390/ijerph120100032
3. Tajkarimi, M.M. et al. (2010) “Antimicrobial herb and spice compounds in food“, Food Control 21 (pp.1199–1218)
Sultanbawa, Y. (2011) “Plant antimicrobials in food applications: Minireview”, in “Science against microbial pathogens: communicating current research and technological advances” A. Mendez-Vials [Ed.] pp. 1084-1093
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