The saturated medium-chain fatty-acid lauric acid (LA) has been associated to certain health-promoting benefits of coconut oil intake. Virgin coconut oil (VCO) is the purest form of coconut oil, essentially water-clear or colourless that consists mainly of medium chain saturated fatty acids. For over many decades, the biological properties of VCO have been widely explored and investigated due to their antimicrobial potentials.
The large concentration of medium chain fatty acids (MCFAs) including lauric acid (LA) and its monoglyceride form, monolaurin makes VCO effective in their mode of actions against pathogenic microorganisms. Thus, VCO could be used as a daily supplement or an alternative remedy against microbial infections.
Coconut was valued as a medicinal plant for centuries in the Thai traditional medicine. Records also show that in theUnited States, coconut oil has been one of the major sources of dietary fats, prior to the introduction of American edible oil (soybean and corn) in the mid-1940s.
Unlike palm oil, coconut oil can be routinely homemade, easily available oil that is natural and free from chemical treatment. Coconut oil has a low oxidation point where oxidation process only takes place after two years of storage, making it very stable due to high presence of saturated fat.
Usage of coconut oil as frying and cooking oil has been well known, but its uses as a cheaper alternative to relatively expensive butterfat in filled milk, filled cheese, and ice cream makings may need more public awareness and promotion.
The non-food application of coconut oil is acknowledged in the production of soaps, rubbers, elastomers, and also derivatives such as alkanolamides. Generally, coconut oil is available in three major forms, which are refined coconut oil (RCO), copra oil (CO), and virgin coconut oil (VCO).
The Asian Pacific Coconut Community in 2003 defines virgin coconut oil as the oil resulting from the fresh and mature kernel (or solid endosperm or meat) of the coconut through mechanical and natural means, either with the presence of heat or not, without any alteration or transformation of the oil. In essence, VCO is produced by wet extraction process of the fresh endosperm of the coconut while CO is obtained by dry extraction process of the dried endosperm of the coconut fruit. The extraction process of VCO does not involve the use of thermal or chemical and also exposure to very high temperatures or UV treatments, making it more beneficial with all of the natural active components such as antioxidants, vitamins, and polyphenols are being retained. On the other hand, RCO is produced by the extraction of the oil from dried coconut flesh, followed by chemical refinement, bleaching, and deodorization processes.
VCO has been acknowledged as the healthiest crop oil and can be extensively used in various fields such as food, beverage, medicinal, pharmaceutical, nutraceutical, and cosmetics. The incredible health benefit of VCO is due to the unique type of saturated fats presents in the oil. Therefore it is considered the healthiest of all dietary oils.
While the other common plant edible oils usually consist of long chain fatty acids (LCFAs), VCO is an exception to this rule by containing both short chain fatty acids (SCFAs) and MCFAs, the latter thus classified as medium chain triglycerides (MCTs).
MCTs are MCFAs esters of glycerol, and edible MCTs oils are normally gained through lipid fractionation from edible fats such as coconut oil and milk. MCTs were originally produced in the late 1940s by Dr Vigen Babayan of the Drew Chemical Company in an effort to find uses for the top fractions of coconut oil fatty acids, thus became commercially available in 1955. Although they are categorised as saturated fats, MCTs outshine the other saturated fats and oils due to their distinctive properties of having shorter chain length and smaller molecules making them more quickly absorbed and metabolised by the body. Due to these distinctive properties, MCTs have been used in the treatment of various malabsorption ailments.
Being a type of saturated fat, MCTs are readily digestible, while LCTs, although it is saturated, are difficult to digest.The term MCFAs refers to a mixture of saturated fatty acids which commonly consists of 6–12 carbons chain.
Coconut oil is about 90% saturated fatty acids and is highly saturated oil. Remarkably, coconut oil has the major amount of caprylic acid, capric acid and LA among the palm oils and can be considered as the most saturated oil compared to palm, soybean, and corn oils and animal fats. Coconut oil is hence a unique vegetable oil because it is the only oil where approximately 50% of the fatty acid composition is LA.
Many of the advantages of coconut oil are attributed o the existence of LA. Similarly, DebMandal & Mandal and Marina et al. declared that the most abundant and powerful MCFAs in VCO is LA which comprises nearly 50% of coconut‟s fat content.
Interestingly, studies had shown that human breast milk and VCO share similar fat content. Kabara and Hayatullina et al. highlighted that 60% of VCO MCFAs is similar in composition to human breast milk. LA and linoleic acids amount to 5% and 15%, respectively, of total fatty acids in human milk that function as determinants of anti-infective activity.
Our body converts LA into monolaurin, a monoglyceride composed of a glycerol unit and it is present in many animals and plants. Monolaurin has been identified by many researchers to be the protective substance that keeps infants against viral and bacterial infections.
It was not a very long time ago that many epidemiological and nutritional studies suggested that the consumption of high amounts of saturated fat and cholesterol led to high blood cholesterol which ultimately left VCO at a disadvantage and received a bad reputation. However, the tides have turned for VCO where recent clinical studies have shown multiple positive outcomes offering counter arguments recognising them as highly valuable and healthy oils. Studies have shown that the use of VCO in diet can regulate blood fats and increase the HDL cholesterol level while decreasing the LDL significantly thus disproving the myth that coconut oil increases cholesterol in the body.
Antimicrobial activities of virgin coconut oil
The high potentials of coconut oil as medicine were ascertained by Kabara in the 1970s, who found coconut oil‟s antibacterial, antiviral, and antifungal activities were exerted by its MCFAs. The recognition of coconut oil antimicrobial activities was also reported by Hierholzer and Kabara which focused on virucidal effects of monolaurin RNA and DNA viruses. Recently, experimental outcomes from many studies discovered that monolaurin had not only antimicrobial activity against various gram-positive and gram-negative bacterial cells [1,3,43] but also antifungal and antiviral properties. Manohar et al. showed that coconut oils, when used as food flavouring agents, exhibited a wide range of antimicrobial activities. Among MCFAs, LA and its derivatives were found to be the most effective antimicrobial agents for foods and cosmetics. The antimicrobial effects of fatty acids are additive and their total concentration is vital for bacterial growth inhibition.
Antibacterial action of coconut oil
VCO was more effective against Bacillus cereus, a gram-positive bacterium compared to E. coli due to the presence of MCFAs and its monoglyceride form especially monolaurin. Widiyarti et al. showed that the antibacterial activity of LA was very potent and was effective against Staphylococcus aureus.
Similarly, the effect of LA on the growth of bacteria was investigated and it was evident from the study that LA was the most effective inhibitor against S. aureus and Pseudomonas aeruginosa, a common opportunistic bacterium that causes infection in immunocompromised individuals. Further, Verallo-Rowell et al. found that VCO was useful in the treatment of atopic dermatitis caused by S. aureus. Wang and Johnson examine the effectiveness of monolaurin on the growth of Listeria monocytogenes, a human foodborne pathogen. A transmission electron scanning (TEM) analysis was done to observe the morphological changes in the bacteria cells. Results of their study showed that cytoplasmic content of treated bacteria cell appeared to separate from cell envelope. Breakage of the cell envelope also was observed.
Moreover, studies on medium-chain saturated and long-chain unsaturated monoglycerides added to supplement infant formula established that both can effectively inactivate a gram-negative bacterium, Haemophilus influenzae while Thaweboon et al. reported that coconut oil exhibited antimicrobial activity against Streptococcus mutans by evaluating its effect on biofilm models formed on salivary-coated microtitre plates. It has been also reported that fatty acids extracts obtained after the hydrolysis of coconut fat showed high antimicrobial potential against gram-positive bacteria, B. cereus and L. monocytogenes and gram-negative bacteria, E. coli and S. enteritidis. Only recently, Odel et al. further proved that LA could hinder the maturity of S. aureus, B. cereus, E. coli, and Salmonella thypimurium, but the inhibition was still lower than the Ciprofloxacin, an antibiotic used to treat a number of bacterial infections.
Antifungal action of coconut oil
Presently, VCO and its MCFAs have been used broadly against fungi and most of the researches were focusing on Candida albicans, the most common and frequently isolated fungus from the human body.
An in vitro study by Arnfinnsson et al. showed that capric acid and LA had the strong ability to inhibit the growth of C. albicans. The result reported that even at low concentration, LA was able to inhibit the yeast cell but still, it required a longer than usual incubation time. The reduction in infectivity titers suggested some fungicidal activity by capric acid and LA. Huang et al. stated that different kinds of fatty acids displayed different patterns of inhibition against oral bacteria. Their study demonstrated that MCFAs had a significant anti-Candida activity while SCFAs and LCFAs showed limited bioactivity against oral fungal species.
An agar well diffusion technique was used to test the susceptibilities of Candida species to coconut oil and the results revealed that at 100% concentration of coconut oil, all the Candida species were sensitive to coconut oil while at the lowest concentration (0.79%), only 35% of Candida species were affected by coconut oil. Among all the species tested, C. albicans showed the highest susceptibility to coconut oil while C. krusei demonstrated the utmost resistance to coconut oil.
Antifungal activity of coconut oil also has been studied by Winarsi and Purwanto  where a vaginal candidiasis patient was successfully treated with zinc enriched VCO that might have acted as an immunostimulants. The antifungal activity of coconut oil against C. albicans was also found to be higher than probiotic, a live microorganism that grants a health benefit on the host.
Antiviral action of coconut oil
The antiviral activity of monolaurin was tested against many enveloped human RNA and DNA viruses and the results concluded that all viruses were reduced in infectivity at 1% concentration of the monolaurin additive. In the presence of LA, Hornung et al. indicated that the replication of vesicular stomatitis virus (VSV) was inhibited by several orders of magnitude where the inhibitory effect was reversible. They reported that the quantity of matrix protein, one of the five functional proteins encoded by the virus placed in the plasma membrane, was found to be noticeably decreasing after the treatment with LA.
Correspondingly, by having coconut oil in the daily diet, Dayrit stated that the viral load of HIV patients could be reduced, showing that it has an antiviral effect. According to Enig, the AIDS organisation, Keep Hope Alive, has documented several HIV/AIDS patients whose viral load reduced to undetectable levels when they added coconut oil to their daily diet or their anti-HIV medication.
The positive antiviral action was seen not only with the monoglyceride of LA but with coconut oil itself indicating that coconut oil was metabolised to monoglyceride forms of caprylic acid, capric acid, and LA to which it must owe its antipathogenic activity. A year later, Enig  claimed that monolaurin could inactivate viruses including HIV, measles virus, HSV, VSV, VV, and cytomegalovirus (CV) to some extent.
In addition, Arora et al. stated that coconut oil was very effective against various viruses with lipid capsules, such as VV, CV, and also Epstein-Barr virus. Yuniwarti et al. investigated the effect of VCO on lymphocyte and CD4 (cluster of differentiating), a surface protein on T lymphocyte, in chicken which had been vaccinated against the avian influenza virus. The study which applied the completely randomised factorial design method concluded that fatty acids of VCO were able to boost the amount of lymphocyte and CD4 on vaccinated or unvaccinated broiler chicken showing that VCO was potentially acting as an immunomodulator which therefore could increase chicken immunity and in combating a viral infection. The antiviral activity of VCO and its MCFAs has been summarised in Table I.
Action mechanism of coconut oil against pathogenic microorganisms
The exact mechanism by which VCO exerts its antimicrobial effects is still largely unknown. Of the coconut derived metabolites, LA may have the most antimicrobial activity. According to DebMandal and Mandal, LA and its monoglyceride found in coconut oil are effective in obliterating a wide variety of lipid-coated bacteria by disintegrating their lipid membranes. The MCFAs in coconut oil principally destroy microbial organisms by disturbing their membranes, thus interfering with virus assembly and maturation. Besides, monolaurin is known to produce highly ordered membranes, which is thought to disrupt membrane function by affecting signal transduction due to blockage of promoters, uncoupling of energy systems, altered respiration state, and altered amino acid uptake.
A key factor in the virucidal activity of monolaurin was associated with a generalised disintegration of the cell envelope signifying that solubilisation of the lipids and phospholipids in the cell envelope had occurred. The viral envelope was found to be affected by fatty acids, causing leakage and at even higher concentrations, a complete disintegration of the envelope and the viral particles occurred.
Recent electron microscopic evidence of several microbes after being exposed to fatty acids suggested that the cell membranes of Clostridium perfringens, Chlamydia trachomatis, Streptococcus agalactiae, C. albicans, and S. aureus were disrupted with subsequent lysis of the bacteria.
The information discussed in this review explains that VCO possesses various types of fatty acids which have been associated with its biological and medicinal properties. Based on the summary compiled herein on the antimicrobial activities of VCO, it is noted that VCO contains various potent bioactive compounds, most of which might have bactericidal, virucidal, and fungicidal benefits with less or no adverse effects. Above and beyond, the emergence of the microbial resistance, together with the low availability of antimicrobial agents which are often opted as the last resorts have created a threat to the medical community and practitioners alike, demands for a continuous need to explore nature in search of new antimicrobial compounds with novel targets and modes of action. In this regard, researchers are neither wrong nor weak to turn their attention towards antimicrobials of the plant origin. Even though there is much research on coconut oil, extensive research and investigation on the antimicrobial potency of VCO are necessary to validate the use of VCO as a valuable antimicrobial agent and exploit the oil‟s potential therapeutic benefits to combat various diseases.