Antimicrobials derived from plants represent an exciting new direction in food safety and product management for the food industry1. Since consumer preference is for natural products with limited perceived chemical adulteration, replacing traditional food additives with effective plant antimicrobials could win acceptance from buyers.
There are three main areas in which plant antimicrobials are of interest to the food industry.
Plant antimicrobials, produced as part of the plant’s own defense response to pathogens and injury, are active against bacteria, viruses, parasites and fungi. As such, they provide a degree of protection against many common spoilage organisms such as molds, bacteria and yeasts. Incorporating specific plant antimicrobials can prevent spoilage, thereby extending shelf–life and consumer acceptance. Moreover, the degree of protection is often optimal under common storage conditions used for foodstuffs.
- Foodborne Pathogen Control
Many plant antimicrobials show effective activity against common foodborne pathogens such as Listeria monocytogenes, Salmonella species and Campylobacter, being either bactericidal or effective for inhibiting bacterial growth. Although much of this evidence comes from in vitro testing, there is proof that plant antimicrobials are also active and effective in food matrices themselves.
- Food Production
There are two areas within food production that could benefit from use of plant antimicrobials – genetic modification and as in-feed additives.
Genetically modifying a plant to express specific antimicrobials can breed crops resistant to certain pathogens, in addition to providing a source of the compound for other uses. Many of the plant antimicrobial peptides are encoded by small, well-conserved genes, which make them ideal for genetic manipulation within a crop. In their review, Nawrot et al. (2014) note that combining different plant antimicrobials for synergism could lead to better crop defense and reduce pesticide usage2.
As in-feed additives, plant antimicrobials might replace antibiotics [reviewed Hintz et al.] and provide a perceived natural protection for food animal production. This could avoid development of resistance in addition to promoting growth and herd health.
Before using plant antimicrobials as food additives, the food industry must determine the stability and integrity of these agents under common food processing workflows. Conditions such as pasteurization, high temperatures, acidity and other denaturing conditions could destroy plant antimicrobials, thus rendering them ineffective. Research is also needed to find out the optimal conditions during storage and packaging for activity, since temperature, pH and salt load also influence antimicrobial activity.
For effective use, food producers can incorporate plant antimicrobials into packaging materials as a bioactive layer to act on the food surface, in addition to adding them directly to the food itself. Researchers have also found that approaches such as microencapsulation or incorporation as emulsions on polymer film also maintain effective antimicrobial activity. It is also possible to deliver the antimicrobial activity by incorporating the agents such as garlic oil in chitosan film used for food packaging, or by use in edible coating layers on the food itself.
Since food matrices and processing workflows vary, it is important, to establish that the chosen antimicrobial will continue to be effective in the environment under consideration. For this reason, food industry researchers must examine each use of plant antimicrobials on a case-by-case basis to establish optimal activity and stability. Moreover, producers also need to consider the method of delivery since many plant antimicrobials could alter the flavor of the foodstuff they protect.
Plant antimicrobials are categorized as GRAS – Generally Regarded As Safe. Most food agencies consider them to be food additives for regulation purposes since they generally fall within the scope of federal pesticide controls that impose maximum permissible residue limits. These agencies also handle requests for authorizations of new compounds.
Globally, most countries require authorization before using a new additive in food. The approvals process may only cover use of plant antimicrobials in a limited number of products. This also applies for plant antimicrobials used in packaging. In the US, the Food and Drug Administration handles regulation, governing the type of food for which an additive is permissible. The situation in the European Union is similar, with the European Food Safety Authority handling legislation and oversight. China has the only national organization that handles food additives, the China Food Additives Association.
Following a literature review, Hintz et al. report that although the use of phytochemicals is increasing, there appear to be no plant antimicrobial peptides (PAMPs) registered for use as food additives. Research is still underway to explore these exciting new tools for food safety.
If you missed any of our earlier blogs on Plant Antimicrobials and the Food Industry, check them out below:
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. Nawrot, R. et al. (2014) “Plant antimicrobial peptides“, Folia Microbiologica 59 (pp.181–196) DOI 10.1007/s12223-013-0280-4
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
Tajkarimi, M.M. et al. (2010) “Antimicrobial herb and spice compounds in food“, Food Control 21 (pp.1199–1218)
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