Natural Antimicrobial Research

Originally Published: November 15, 2017
Last Updated: December 21, 2020
Some herb extracts, such as thyme, sage, oregano and rosemary, have antimicrobial properties.

Natural Antimicrobial Research

In his presentation, “Emerging Research to Practical Approaches on Natural Antimicrobial Use,” Mathew Taylor, Ph.D., Texas A&M University, shed light not only on the use of natural antimicrobials, but he also explained why there isn’t a host of new compounds to meet the demand. GRAS approval for food additives is an expensive, time-consuming process that requires demonstration of the safety of the compound, in the manner it will be used, before it enters the market. Many spice extracts have antimicrobial properties, for example, but they are GRAS-based on their use as flavorants and aromatics.

Research on plant-derived antimicrobials is extensive, yet it’s scattered across journals all over the world. Well-devised summaries are lacking. However, the data reveal they work very well in certain applications. Some of the extracts, as well as some of the individual components [within extracts], possess powerful antimicrobial activity that inhibit not only spoilage microbiota, but also pathogenic microbes, Taylor said.

Most of the data are on monophenols, such as essences of cinnamon, thyme, oregano, sage and ginger. “We have very good information on what organisms they work against; which ones they don’t; which cultivars of plants are best for harnessing or harvesting; at what stage of maturity of the plant; what conditions of use; and what are their organoleptic impacts. We know the most about these,” Taylor added.

Organo-sulfur extracts from garlic, onion and shallots (members of the genus Allium and family Cruciferae) are potent antimicrobials. These compounds cause cell death in Grampositive and Gram-negative bacteria, and in fungi.

Biopreservation, another means of extending shelflife and food safety, utilizes natural or controlled microbiota and/or antimicrobial compounds. There are three key forms: fermentative non-pathogenic microbes, principally the lactic acid bacteria (LAB); fermentates from non-pathogenic fermentative microbes that are purified and added to other foods, such as acids and bacteriocins; and bacteriophages. For example, Carnobacterium maltaromaticum is approved for RTE meats as an antilisterial agent in the U.S. and Canada. Lactobacillus and Pediococcus spp. are approved for fresh and processed meat safety by FDA/USDA. FDA has provided GRAS affirmation for many LAB products used in fermentation processing, but very few approvals in biopreservatives.

Since its introduction in 1958, the FDA’s GRAS list has evolved from an affirmation to a notification process. This chart shows the average FDA response time to a filing entity from 1998-2005. GRAS approval for food additives normally is an expensive, time-consuming process, noted Taylor.

Click here for a downloadable copy of the chart.

A third category, antimicrobial metabolic products, are produced by non-pathogenic microbes via industrial fermentations. They are comprised by some combination of acids, antimicrobial peptides, peroxides and miscellaneous antimicrobials. Nisin, mixed fermentates, natamycin (an antifungal) and poly-L-lysine are examples that present options for clean label, depending on their usage/application. Some may have greater restrictions on labeling, but the natural aspect to this ferment antimicrobial product, despite these being traditional antimicrobials, may be successfully navigated for food safety, Taylor suggested.

Combining antimicrobials provides opportunities for synergism. Pairs or even three-compound applications have been reported to demonstrate synergistic inhibition of microbes. Pairing antimicrobials with thermal or non-thermal physical processing may reduce overall antimicrobial utilization without safety or quality detriment.

Taylor cautioned that replacing traditional antimicrobials with clean label alternatives requires careful planning. Naturally occurring acidulants may replace organic acid salts or inorganic acids for pH control, but the impact on pH control must be understood. “If you’re replacing humectants for water activity control, again, do you gain the same functionality?” he asked. If one compound is taken out, something must be added that yields the same functionality. How much must be added? What are the side effects?

It’s important to understand whether the antimicrobial will work within the food itself, because physical or chemical interactions may render it ineffective. “If it’s a hydrophobic antimicrobial, does it partition into your fat phase? What’s the impact on the pH?” Taylor asked.

There also should be a deep, intimate knowledge of the microbial ecology of the food before considering replacing compounds, he stressed. For example, susceptibility of Listeria monocytogenes, for example, to some bacteriocins (like nisin) can be reduced when the bacterial cells are in the resting stage. However, when replicating and growing, the pathogen causes gastrointestinal disease in immunocompromised individuals, and it can cause spontaneous abortions in pregnant women.

Clean label opens a lot of doors, but it closes some too, he concluded. One cannot sacrifice the safety and wholesomeness of the food just for a clean(er) label.

“Emerging Research to Practical Approaches on Natural Antimicrobial Use,” Matthew Taylor, Ph.D., Associate Professor, Dept. of Animal Science, Texas A&M University,

This presentation was given at the 2017 Clean Label Conference. To download presentations from this event, go to

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