Essential Oils as Natural Food Antimicrobial Agents

                  Essential oils are scented and flavorful liquids that are extracted from various amounts of plant material such as fruits, flowers, bark, roots, wood, etc. For hundreds of years, essential oils have been used in holistic practices, medicine, cosmetics, and have been newly introduced to food. Recently, scientist are highly considering various amounts of essential oils to be used in food preservation for vegetables, fruits, cereal, and also grains. Food-borne diseases are an extreme problem in not only the U.S, but across the world because of increased consumerism of packaged food. This severe problem calls for a more effective preservation strategy. Owing to the fact that antimicrobial agents are added to the food packaging, sometimes by itself or integrated, high amounts of illnesses are continuously being contracted because of bacteria. Essential oils are to be considered a natural antimicrobial agent because of its functional group called phenolic. Vergis J. explains that essential oils are well known for its antibacterial, antiviral, antimycotic, antiparasitic, and antioxidant properties due to the presence of phenolic functional group; however gram-positive organisms are found more susceptible to the action of the essential oils. (Vergis. J.) Additionally, essential oils enhance the shelf-life of products that are packaged, control the growth of microbes, and lower concerns regarding preservations that have high amounts of chemicals within them. This review paper will offer the overview of essential oils and their vital role as natural antimicrobial agents, knowledge about their antibacterial properties, their possible role in food preservation, and food safety.

                 In today’s society, food safety is a main concern within our communities. Syeda Batool stated that the report of WHO in 2005, there were about 1.8 million deaths caused by diarrhea (food-borne illness), and these diseases were due to the use of contaminated food and water. The main cause of food-borne illnesses is the use of food contaminated by microbial pathogens, toxins, or radioactive components.” (Batool, Syeda) Food-borne illnesses, which could be a mild or deadly case, is caused by bacteria or pathogens that contaminate food. The main food-borne pathogens that is known to contaminate food is Clostridium botulinum, Staphylococcus aureus, Campylobacter jejuni, Bacillus cereus, Listeria monocytogenes, Cryptosporidium, and Escherichia coli. Fresh and healthy food has increased in demand because of people that are becoming more health conscious. This is becoming a challenge to keep these types of foods fresh. The usage of chemical preservatives is starting to have a negative impact on the consumer, although it is used to prevent spoilage and diseases. “Traditional food preservation methods are less efficient in reducing the growth of food-borne pathogens in food products, and the ever-increasing demand for chemical-free food has paved the way for antimicrobials to be used in food industry” (Basak, S.) Antimicrobials are used to increase shelf life of food and increase food quality and safety. Antimicrobials can be synthetic or natural, however, natural microbials such as essential oils, are receiving much more attention in importance than synthetic antimicrobials. “Synthetic preservatives are approved by government agencies for human use, many of these preservatives still threaten our health.” (Sajid, Muhammad) Scientist and researchers are turning toward essential oils and natural products because of their antimicrobial agents and health benefits.

            Essential oils, often called volatile odoriferous oil, are considered secondary metabolites. This is a major key for plant defense because of their antimicrobial properties or disease-controlling agents. Essential oils contain properties of antioxidants and antimicrobial at the same time, which is known to be a healthier option for food preservation in contrast to synthetic preservatives. In order for essential oils to be useful in food preservation, scientist must have detailed knowledge about their properties. Scientist have been conducting research to find out the antimicrobial potential of essential oils in many plant sources such as, herbs, spices, fruits, and vegetables. “There are more than 1350 plants with antimicrobial activities and more than 30,000 antimicrobial components have been extracted from plants.” (Gyawali, R.) This wide range of antimicrobial components extracted from plants are essential in the growth of natural food preservation. Essential oils have an inhibitory effect against gram-positive bacteria. The structure of the antimicrobial component, chemical composition, and its concentration determine their efficacy. “The main compounds with antimicrobial activity are phenols which include terpenes, aliphatic alcohols, aldehydes, ketones, acids, and isoflavonoids.” (Gyawali, R.) There are also 4 main active compounds that can be grouped by their chemical structures: terpenes, terpenoids, and phenylpropenes.

                                     (Santos, F.)

      Chemical structures of terpenes, terpenoids, phenylpropenes, and others. (Santos, F.)

                   Terpenes, often accompanied with a strong odor, are organic compounds that is produced by a variety amounts of plants including cannabis. It is one of the key ingredients in essential oils. “Terpene-containing plant oil has been used to treat various diseases without knowing the exact functions or the mechanisms of action of the individual bioactive compounds.” (Davidson, P.) However, terpenes are known for their anti-inflammatory, anti-tumorigenic, and neuroprotective activities. Scientist has studied that terpenes are hydrocarbons and are synthesized in cytoplasm of plant cells. “Terpenes have a hydrocarbon backbone which can be rearranged into cyclic structures by cyclases, thus forming monocyclic or bicyclic structures.” (Davidson, P.) Because of this, terpenes as single compounds, do not have a high antimicrobial activity. This was shown from a study that was conducted against gram-negative pathogens, and terpenes alone had no antimicrobial activity even in large concentrations.

                 Next are terpenoids which are similar to terpenes, but terpenoids are more complex. “Terpenoids are terpenes that undergo biochemical modifications from enzymes, which add oxygen and move methyl groups.” (Hyldgaard, M.) Because of their complexity, scientists found out that terpenoids could be subdivided into additional groups such as: esters, ketones, and epoxides. “The antimicrobial activity of most terpenoids is linked to their functional groups, and it has been shown that the hydroxyl group of phenolic terpenoids and the presence of delocalized electrons are important for antimicrobial activity.” (Hyldgaard, M) This is because terpenoids contains a large group of antimicrobial compounds that are active against microorganisms. “Dorman and Deans investigated the effect of many terpenoids against 25 different bacterial strains, and showed that all terpenoid compounds, except borneol and carvacrol methyl ester, exhibited a broad antimicrobial activity. The antimicrobial activity of carvacrol, thymol, linalool, and menthol were evaluated against Listeria monocytogenes, Enterobacter aerogenes, E. coli, and Pseudomonas aeruginosa.” (Hyldgaard, M.) It was reported that carvacrol was the most active compound in the study which confirms there is high amounts of antimicrobial activity in terpenoids. This experiment was important because it validates that essential oils with terpenoids are natural antimicrobial agents.

              The next active compound mentioned is Phenylpropenes. This organic molecule is found in a variety of plants and contribute to the flavors of many herbs and also spices. Reyhan Irkin describes phenylpropenes, often called phenylpropanoids, have their name from the six-carbon aromatic phenol group and the three-carbon propene tail of cinnamic acid, produced in the first step of phenylpropanoid biosynthesis. (Irkin, R.) Even though phenylpropenes make up a small part of essential oils, scientist are knowledgeable on the compound. Phenylpropenes that have been continuously studied are cinnamaldehyde, vanillin, isoeugenol, eugenol, and safrole. Phenylpropenes antimicrobial activity is determined by the number of substituents on the aromatic ring, the temperature, the growth medium, and microbial strains. Eugenol, one of the most important phenylpropenes, plays a huge role in essential oil. Its antimicrobial activity can permeabilize the cell membrane and interact with proteins which increases the transport of potassium and ATP out of cells. (Irkin, R.) Additionally, eugenol has shown that it can enhance small changes of fatty acids in Pseudomonas fluorescens, E. coli, Brochotrix thermosphacta, S. enterica, and S. aureus, and cell damages to E. coli and B. thermosphacta cells. (Irkin, R.) This important action that eugenol inhibits show that phenylpropenes can be used in treating many viruses and food-borne illnesses.

          The breakdown on these active compounds in essential oils confirm that they have high antimicrobial activity against gram-positive and negative bacteria. Because of this, scientist and researchers can use essential oils as natural food antimicrobial agents. Studies has shown that synthetic preservatives increase food shelf-life, but can be extremely harmful to the human body because of its man-made chemical substances. Researchers are seeing bacteria growth and increased health risk with synthetic preservatives. Sodium benzoate, a synthetic preservative, can cause hyperactivity and asthma in children. Sodium nitrite could cause pancreatic cancer and other health problems if eaten excessively. Furthermore, butylated hydroxyanisole affects the neurological system of the brain, alters behavior and has a potential to cause cancer. (Tongnuanchan, P.) The health concerns in synthetic preservatives calls for the use of natural preservatives.

                   Chouhan explains that essential oils from herbs and spices like clove, oregano, rosemary, thyme, sage, and vanillin are the most effective against spoilage and pathogenic microorganisms like L. monocytogenes, E. coli, P. fluorescens, L. sake, S. aureus, and B. subtilis. (Chouhan, S.) As mentioned earlier, phenolic compounds are the reason plant essential oils have such a great antimicrobial activity. Vegetables and fruit contain high antimicrobial agents as well, and fight against spoilage and pathogenic microbes. “Extracts of capsicum annum showed antimicrobial effects against S. typhimurium in minced beef; similarly, pomegranate extracts reduced the growth of E. coli. Citrus peel extract, lemon grass, and lime peel extracts showed great antimicrobial effect against B. cereus, S. typhimurium, and S. aureus.” (Chouhan, S.) Extracts of capsicum, pomegranate, citrus peels, lemon grass, and lime peels are known for fighting against bacteria and diseases. These extracts listed are also used in holistic practices and aromatherapy because of the great benefits they display against diseases.

                  Essential oils are used in a variety of different ways; from flavorings, scents, medicine, and aromatherapy. It has newly been introduced to food and food preservatives. The benefits of using natural preservatives in food will increase human health and benefit us tremendously. The active compounds that makeup essential oils are the reason for their high antimicrobial activity. It is vital for researchers and scientist to control food safety and keep our foods healthy, which is why natural preservatives are becoming popular. Essential oils have antimicrobials that can destroy the main food-borne diseases, which is Clostridium botulinum, Staphylococcus aureus, Campylobacter jejuni, Bacillus cereus, Listeria monocytogenes, Cryptosporidium, and Escherichia coli. (Vergis, J.)These diseases are known to cause serious illnesses and death in not only the U.S, but around the world. Additionally, essential oils are imperative to human health and show great benefits if used as natural preservatives. Owing to the fact that these oils contain natural compounds, the increase for natural antimicrobials are on the rise in the food market. Hopefully, essential oil preservatives will be applied to the many packaged foods we eat daily.

Citations

1. Arshad, Muhammad Sajid, and Syeda Ayesha Batool. “Natural Antimicrobials, Their Sources and Food Safety.” Intech Open, IntechOpen, 6 Sept. 2017.
2. Basak, S, and P Guha. “A Review on Antifungal Activity and Mode of Action of Essential Oils and Their Delivery as Nano-Sized Oil Droplets in Food System.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, Dec. 2018.
3. Chouhan, S, et al. “Antimicrobial Activity of Some Essential Oils-Present Status and Future Perspectives.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, 8 Aug. 2017.
4. Davidson, P. Michael, et al. “Chemical Preservatives and Natural Antimicrobial Compounds.” ASMscience, American Society of Microbiology, 1 Jan. 2013.
5. Gyawali, Rabin. “Natural Products as Antimicrobial Agents.” NeuroImage, Academic Press, 8 June 2014.
6. Hyldgaard, M, et al. “Essential Oils in Food Preservation: Mode of Action, Synergies, and Interactions with Food Matrix Components.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, 25 Jan. 2012.
7. Irkin, Reyhan, and Ozlem Kizilirmak Esmer. “Novel Food Packaging Systems with Natural Antimicrobial Agents.” SpringerLink, Springer, 7 Mar. 2015.
8. Santos, Fortino. “Essential Oils from Aromatic Herbs as Antimicrobial Agents.” NeuroImage, Academic Press, 6 Sept. 2011.
9. Tongnuanchan, Phakawat, and Soottawat Benjakul. “Essential Oils: Extraction, Bioactivities, and Their Uses for Food Preservation.” The Canadian Journal of Chemical Engineering, Wiley-Blackwell, 2 June 2014.
10. Vergis, J, et al. “Essential Oils as Natural Food Antimicrobial Agents: a Review.” Current Neurology and Neuroscience Reports., U.S. National Library of Medicine, 2012