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Use of essential oils in food preservation
M. Laranjo1,2, A. M. Fernández-Léon1,2, M. E. Potes1,3, A. C. Agulheiro-Santos1,4 and M. Elias1,4*
1 ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Universidade de Évora, Évora, Portugal
2 IIFA-Instituto de Investigação e Formação Avançada, Universidade de Évora, Évora, Portugal
3 Departamento de Medicina Veterinária, Escola de Ciências e Tecnologia, Universidade de Évora, Évora, Portugal
4 Departamento de Fitotecnia, Escola de Ciências e Tecnologia, Universidade de Évora, Évora, Portugal
New alternatives for food conservation and preservation are now emerging, as many studies have shown that the use of
synthetic preservatives and chemical additives is leading to intoxication, cancer and other degenerative diseases. This has
led to a growing consumer concern and the desire to consume healthier products containing natural preservatives and
additives instead of synthetic ones. This generates the need to look for conservation alternatives that cover the same
antimicrobial properties and compatibility with food. In this search, new antimicrobial agents of natural origin, as is the
case of essential oils (EOs) obtained from aromatic and medicinal plants, have been found. EOs have antimicrobial activity
against a wide range of microorganisms and antioxidant activity, this is generally attributed to phenolic compounds owned
by EOs. Many studies in vitro have defined EOs as effective antimicrobial and antioxidant compounds, but they are not
much used in industry. Mediterranean dietary food products (meat and meat products, cheeses and fruits) are highly
appreciated by consumers; their preservation with EOs would represent an added value. The present study reviews the
existing research work on the use of EOs as food preservatives as an alternative to synthetic preservatives and chemical
additives in Mediterranean food products.
Keywords food safety; antibacterial; antifungal; phenolic compounds; minimum inhibitory concentration
1. Introduction
The main cause of food spoilage is the occurrence of different types of microorganisms (bacteria, yeasts and moulds).
This problem economically affects manufacturers, distributors and consumers. It is estimated that more than 20% of
all food produced in the world is spoiled by microorganisms (1). The control of physical, chemical and particularly
microbiological factors is essential for food preservation (1, 2).
In recent years, consumers prefer food of easy preparation and good quality, safe, natural and low processed, but with
longer shelf-life. With food preservation technologies, more long-lasting products are obtained, maintaining their initial
nutritional and sensory characteristics (1, 3-5).
For many years, synthetic preservatives have been used in the food industry, the most used being antimicrobial
preservatives, but at present there are studies indicating that the consumption of chemical additives can lead to allergies,
intoxications, cancer and other degenerative diseases (1, 6). For this reason, they are depreciated by consumers, which
motivates the need to look for other alternatives. This search has uncovered new antimicrobial agents of natural origin,
as substitutes of those traditionally used (7, 8).
1.1 New alternatives for food preservation
One of the alternatives more studied is "natural conservation", which is the use of natural antimicrobial preservatives
present in plants, animals or microorganisms, and especially those derived from extracts of various types of plants and
parts of plants that are used as flavouring agents in some foods (6-9).
Antimicrobials are used in food to control natural spoilage processes (food preservation) and to control microbial
growth (food safety) (10). The difficulty is to extract, purify, stabilise and incorporate these antimicrobial into food
products without affecting its sensorial quality and safety (1).
The FDA (Food and Drug Administration) treats antimicrobial agents of natural origin as GRAS (Generally
Recognized As Safe) type products, including plant products from which essential oils (EOs), oleoresins and natural
extracts, as well as their distillates, are obtained (1, 11).
Recently, the food industry has shown a considerable interest in the extracts and EOs of aromatic plants due to their
ability to control the growth of pathogenic microorganisms (1-14).
1.2 Medicinal and aromatic plants and EOs
Medicinal and aromatic plants (MAPs) are very important in various fields, such as the pharmaceutical, perfumery and
cosmetic industries (15). MAPs constitute a high percentage of the natural flora, 80% of the world's population uses
traditional MAPs-based medicines to treat various human health problems. More than 9000 native plants have been
identified and recorded for their curative properties, and about 1500 species are known for their aroma and flavour (15,
Antimicrobial research: Novel bioknowledge and educational programs (A. Méndez-Vilas, Ed.)
EOs are volatile substances, although is presented as a natural liquid that is extracted from different parts of
medicinal and aromatic plant (flowers, buds, seeds, leaves, twigs, bark, herbs, wood, fruits and roots) (17). EOs are
important for plant protection, because they have antimicrobial, antiparasitic, insecticidal, antiviral, antifungal and
antioxidant properties (18). There has been an increasing demand in medicine, perfumery and cosmetic industries.
Furthermore, the use of EOs in food industry, as antioxidants, flavourings or colorants, has also increased and they
can also be used for food preservation (17, 19).
Driven by the growing interest of consumers for natural ingredients and their concern about potentially harmful
synthetic additives, the global demand for EOs is increasing nowadays, more than 250 types of EOs are marketed
annually on the international market (15, 20, 21).
Before these products can be used, they have to be extracted from the plant matrix. Different methods can be used for
this purpose; expression, distillation, solvent extraction and emergent methods (21).
Expression or cold pressing is mainly used for the isolation of citrus peel oils because of the thermal instability of the
aldehydes contained therein. This method has the advantage of low heat generation during the process, but the
disadvantages are that it gives low yields and low purity (21).
Distillation process consists basically in placing the plant material in boiling water or heating by steam, the heat
applied causing break down of cell structure of plant material and releasing the EOs. The advantage of this method is
that the volatile components can be distilled at temperatures lower than the boiling points of their individual
constituents and are easily separated from the condensed water. Considering the manner in which the contact between
water and the original matrix is promoted, distinguishes three types of distillation has been proposed: hydrodistillation,
steam distillation and water/steam distillation (21, 22).
Solvent extraction allows to extract EOs with organic solvents (acetone, hexane, petroleum ether, methanol or
ethanol), because of their hydrophobic and nonpolar character. In this method, solvent is mixed with the plant material
and heated to extract the essential oil. Then, it is filtrated and concentrated by solvent evaporation, later it is mixed with
pure alcohol to extract the oil at low temperatures and finally the alcohol is evaporated and the EO stays pure. This
method has some disadvantages, such as the presence of traces of the solvents in the essential oil (dangerous for health)
and the production of effluents (dangerous for the environment) (21).
Due to concerns about the environment, new separation techniques are emerging that reduce energy consumption and
CO2 emissions. Emergent methods for extracting OE are microwave assisted extraction, ultrasonic assisted extraction
and supercritical fluid extraction.
Once the EOs are extracted, it is necessary to know their chemical composition, because their antimicrobial activity
depends on their chemical composition.
There are different methods to analyse EOs, but gas chromatography (GC) has been described as the most suitable
method to the analysis of EOs (21, 23). Nowadays, GC coupled with mass spectrometry is used to improve the
separation of the different EOs compounds.
2. Composition of EOs
The chemical composition of EOS is complex; there may be around 20 to 60 different bioactive components in each
EO. However, generally only 2-3 major components are present at a fairly high concentration (20-70%) compared to
other components present in traces (16). Some factors that may affect these constituents include the geographic
location; the environment, the stage of maturity harvest season or extraction method (15, 16).
EOs are secondary metabolites formed by plants, these metabolites protect to the plant against conditions of biotic
and abiotic stress. Most EOs are composed of terpenes, and other aromatic and aliphatic constituents with low
molecular weights (11, 15).
Terpenes are represented by the chemical formula (C5H8)n and are composed of isoprene units. These compounds are
classified into several groups, such as monoterpenes (C10H16), sesquiterpenes (C15H24), diterpenes (C20H32), and
triterpenes (C30H40).
The major bioactive components (90%) of EOs oils are monoterpenes, that are synthesized within the cytoplasm of
the cell through the mevalonic acid pathway (15). Some compounds include monoterpene hydrocarbons (p-cymene, -
pinene and -terpinene), oxygenated monoterpenes (camphor, carvacrol, eugenol and thymol), diterpenes (kaurene and
camphorene), oxygenated sesquiterpenes (spathulenol and caryophyllene oxide), monoterpene alcohols (geraniol,
linalool and nerol), sesquiterpene alcohol (patchoulol), aldehydes (citral and cuminal), phenols (eugenol, thymol,
carvacrol, and catechol) and coumarins (fumarin and benzofuran) (15, 16).
Generally, the EOs possessing the strongest antibacterial properties against foodborne pathogens contain a high
percentage of phenolic compounds, such as carvacrol, eugenol and thymol. Phenolic compounds possess great structural
variations and are one of the most diverse groups of secondary metabolites. The hydroxyl (-OH) groups in phenolic
compounds are thought to cause inhibitory action as these groups can interact with the cell membrane of bacteria to
disrupt membrane structures and cause the leakage of cellular components (8).
The major components of a number of EOs with antibacterial properties are presented in Table 1.
Antimicrobial research: Novel bioknowledge and educational programs (A. Méndez-Vilas, Ed.)
Table 1 Major components of selecteda EOs that exhibit antibacterial properties.
Common name of EO Latin name of plant source Major components References
Cinnamon Cinnamomum zeylandicum Trans-cinnamaldehyde (24)
Cinnamon Cinnamon casia Trans-cinnamaldehyde
Clove Syzygium aromaticum
Eugenyl acetate
Oregano Origanum vulgare
(25, 28-30)
Rosemary Rosmarinus officinalis
Bornyl acetate
(37, 40-42)
Sage Salvia officinalis L.
Sage Salvia triloba Eucalyptol (42)
Thyme Thymus vulgaris Thymol
(2, 24)
(41, 43)
(44, 45)
(37, 46, 47)
Adapted from Burt et al. (11)
a EOs which have been shown to exert antibacterial properties in vitro or in food models.
According to the study carried out by different authors, the percentages of main bioactive compounds of EOs named
above are: cinnamon 65 % Trans-cinnamaldehyde (24), clove 75-85 % eugenol (8), oregano 64 % thymol (31),
oregano 15 % p- Cymene and 30 % carvacrol (30%) (48), rosemary 14 % 1,8-cineole (37), sage 42 % α-tujone
and 15 % camphor (39), thyme 64 % thymol (2), and thyme 44 % linalool (49).
EOs present different bioactive compounds, as well as different percentage of them, this explain the differences that
exist between them in their behaviour against microorganisms, that is to say, their antimicrobial activity (8, 50).
3. EOs antimicrobial activity
The antimicrobial activity is mediated by a series of biochemical reactions, which are dependent on the type of chemical
constituents present in the EOs (15, 50).
3.1 Mechanism of antimicrobial action of EOs
The mechanisms of antimicrobial action of EOs are not only different depending on the main chemical of EOs, also if
the action is on Gram-positive or Gram-negative bacteria, or on fungi, that are found in food (11).
3.1.1 Mechanism of antibacterial action
Firstly, EOs destabilize the cellular structure, destroying membrane integrity and increasing permeability, and
disrupting cellular activities, as for example energy production and membrane transport (15).
The disruption of the cell membrane causes the alteration of various vital processes, such as nutrient processing, the
synthesis of structural macromolecules, and the growth regulators (15).
Owing to their lipophilic nature, EOs are easily penetrable through the bacterial cell membranes, causing to the
leakage of cellular components and loss of ions (15, 51). Also antibacterial effects of EOs produce the alteration of
proton pumps, and the depletion of the ATP (50), this alteration may cause a cascade effect, resulting in other cell
organelles being affected.
The antibacterial effect of EOs constituents, such as thymol, menthol and linalyl acetate, is due to a perturbation of
the lipid fraction of bacterial plasma membranes (52), while carvacrol changes the composition of fatty acids, which
Antimicrobial research: Novel bioknowledge and educational programs (A. Méndez-Vilas, Ed.)
affects the membrane fluidity and permeability, and trans-cinnamaldehyde enters the periplasm of the cell and disrupts
cellular functions (53).
3.1.2 Mechanism of antifungal action
The antifungal actions of EOs are similar to that of antibacterial mechanisms by direct contact with the fungus, but also
EOs have antifungal activity in vapour phase, this effect is mainly for moulds (21, 54).
By contact, EOs penetrate and altered the fungal cell wall and cytoplasmic membranes by a permeabilisation process,
which disintegrate the mitochondrial membranes (15).
The vapour phase generated by EOs attack the life cycle of some moulds in the stage of germination, affecting the
growth of hypha and sporulation. The inactivation of conidia by EOs is the key process of inhibition, because conidia
are stable to heat, light and chemical compounds, being difficult to eliminate (21).
3.2 Antimicrobial effects of EOs
EOs may inhibit the growth of bacteria (bacteriostatic) and of fungus (fungistatic) or destroy bacterial cells
(bactericidal) and fungus (fungicide), but it is difficult to distinguish it. Thus, antimicrobial activity can be measured as
the minimum inhibitory concentration (MIC), which is the lowest concentration of an antimicrobial that inhibits the
growth of a microorganism after incubation (11).
3.2.1 Antibacterial effects
Some of the most severe foodborne bacteria are Bacillus cereus, Escherichia coli, Listeria monocytogenes, Salmonella
spp. and Staphylococcus aureus (25).
Bacillus cereus is a Gram-positive bacterium producing spores and forming both thermostable and thermolabile
toxins widely distributed in the environment, which can be transmitted to humans through contaminated foods. Studies
have shown that EOs of rosemary inhibited the growth of this bacterium with a MIC of 0.2 µL mL-1 (11, 55).
According to the study of different authors on antimicrobial activity, EOs of clove, oregano, rosemary, sage and
thyme were good inhibitors of the growth of E. coli, with a MIC range of 0.4-10 µL mL-1 (11, 56-59). Although E. coli
(Gram-negative bacilli) lives in the intestine, it can reach food by poor manipulation or hygiene.
EOs of clove, oregano, rosemary, sage and thyme also presented antimicrobial action in L. monocytogenes (Gram-
positive) with a MIC value of 0.15-0.45 µL mL-1 (11). L. monocytogenes causes listeriosis, which is a foodborne
disease, but that occurs in sporadic cases or in outbreaks.
Salmonella spp. (Gram-negative bacilli) leads to salmonellosis, which is the most common cause of foodborne illness
and it is transmitted by direct contact or cross-contamination during handling. EOs of clove, oregano, rosemary, sage
and thyme produced great inhibition in the growth of this bacterium, with MIC value of 1.2- ˃20 µL mL-1 (11, 56),
being oregano the one that presented greater inhibitory power.
Shan et al. (58), the EOs of cinnamon, oregano and clove were found to be effective against Salmonella enterica, but
the clove extracts possessed the highest antibacterial activity (15).
S. aureus (Gram-positive bacilli) can produce a wide range of diseases, ranging from skin and mucosal infections,
but it may also affect the gastrointestinal tract, through the intake of food products contaminated with staphylococcal
Different studies confirmed that EOs clove, oregano, rosemary, sage and thyme were effective in inhibiting S. aureus
growth, on MIC value of 0.2-10 µL mL-1 (11, 44, 56, 59).
In a study by Radaelli et al. (60), a major foodborne disease-causing agent, Clostridium perfringens (Gram-positive),
was inhibited by EOs of rosemary with a MIC value of 10 mg mL-1. C. perfringens is one of the most common causes
of food poisoning. It often happen when food is prepared in large quantities and kept warm for a long time before
serving them, which is why outbreaks of these infections are usually related to catering events.
EOs of MAPs as is showed in the Table 2, have antimicrobial activity on other pathogenic bacteria.
Table 2 Antibacterial activity against human pathogens.
Common name of EO Inhibited microorganisms References
Cinnamon Enterobacteriaceae
Streptococcus pyogenes
Streptococcus pneumoniae
Enterococcus faecium
Acinetobacter lwoffii
Enterobacter aerogenes
Klebsiella pneumoniae
Proteus mirabilis
Pseudomonas aeruginosa
(15, 61)
Antimicrobial research: Novel bioknowledge and educational programs (A. Méndez-Vilas, Ed.)
Mycobacterium smegmatis
Oregano Clostridium perfringens
Salmonella choleraesuis
Bacillus subtilis
Pseudomonas aeruginosa
Shigella sonnei
Sarcina lutea
(15, 21)
Rosemary Bacillus subtilis
Streptococcus agalactiae
Streptococcus epidermidis
Proteus vulgaris
Proteus aeruginosa
Klebsiella pneumoniae
Enterococcus faecalis
(41, 62)
Sage Providencia stuartii
Shigella sonnei
Sarcina lutea
Brochothrix thermosphacta
(15, 62)
Thyme Clostridium perfringens
Shigella sonnei
Sarcina lutea
Brochothrix thermosphacta
(21, 41)
3.2.2 Antifungal effects
In the food industry there is great interest in EOs derived from MAPs due to their property of controlling the growth of
pathogenic microorganisms, such as Fusarium spp., Aspergillus spp., among others, which have been reported as
causative agents of diseases caused by food and/or decomposition of the same (1).
The EOs have been used against a broad range of fungal pathogens, as is showed Table 3.
Clove essential oil showed a MIC value of 0.062 and 0.125 % (v/v) against Candida albicans and Aspergillus niger,
respectively. Rosemary EO is also effective against C. albicans and A. niger, but with MIC values of 0.25 and 1.0 %
(v/v), respectively (15).
The EOs of thyme and clove completely inhibited the mycelium growth of Aspergillus flavus (14).
The major chemical compound of clove, eugenol, was proved to produce permanent damage to the cells of C.
albicans and was considered an efficient antifungal agent, with a MIC value of 1.0% v/v (63).
EOs of clove, cinnamon and oregano were effective against Aspergillus parasiticus and Fusarium moniliforme,
because they caused damage in mycelium growth and mycotoxin-producing ability (64).
Table 3 Antifungal activity against human pathogens.
Common name of EO Inhibited microorganisms
Cinnamon Candida albicans
C. parapsilosis
C. krusei
Aspergillus flavus
Clove Fusarium spp
Oregano Phytophthora infestans
Botrytis cinerea
Rosemary Phytophthora infestans
B. cinerea
Thyme Fusarium oxysporum
F. verticillioides
Penicillium expansum
P. brevicompactum
Aspergillus flavus
A. fumigatus
Alternaria alternata
Adapted from da Cruz-Cabral et al. (65)
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4. Use of EOs in food industry
4.1 Meat and meat products
Usually, the antimicrobial effect of EOs is higher in vitro than in food products. This might be explained by the
availability of more nutrients in food products than in laboratory media. Nutrient-rich matrices, such as meat and meat
products, may enhance bacterial repair and turnover of cellular components, which may increase the resistance of
bacterial populations to many different stresses (66). Still, there are a number of other reasons that may influence the
antimicrobial effect of EOs in foods (67). The fat contents of traditional meat products are considerably high and EOs
are soluble in lipids, which taken together with the usual low pH that increases the solubility of the EOs and the typical
low aW that reduces the aqueous phase of food products increasing the contact between EOs and spoilage or foodborne
microbiota, enhances their antimicrobial effect.
The use of EOs to improve both food safety and shelf-life of meat products has been reported mainly in beef,
chicken, lamb or rabbit fresh meat (2, 47, 68, 69).
However, only a few studies have described the use of EOs as food ingredients (70-72). Application of EOs to food
products is uncommon and mainly limited to cooked meat products. The application of thyme and cinnamon EOs in
ham has been shown to significantly decrease the L. monocytogenes population (70). Furthermore the shelf-life of
mortadella has been extended with the use of rosemary/thyme EOs (72), while the shelf-life of bologna sausages was
extended using oregano EO (71). García-Díez and colleagues (73) reported the improved safety of dry-cured sausages
through the antibacterial effect of garlic and oregano EOs against Salmonella spp., L. monocytogenes and S. aureus. At
concentrations of 0.5% and 1% clove EO restricted the growth of L. monocytogenes in meat at both 30 °C and 7 °C
The antimicrobial effect of EOs is associated with their composition, the characteristics of each food product and the
specific microorganisms to be eliminated. Additionally, several other factors may affect the antimicrobial effect of EOs
in food products, namely heat treatments, smoking, chemical preservatives and packaging (11).
The use of EOs in combination with other technologies, such as thermal treatments, high isostatic pressures (HIP),
pulsed electric field and active packaging against foodborne pathogens have also been reported (75, 76). For example,
low concentrations of orange, lemon and mandarin EOs (0.2 mL/mL) combined with a mild heat treatment (54 °C/10’)
showed synergistic lethal effects, inactivating more than 5 log units of bacterial cells, thus demonstrating the potential
of successful combined treatments for food preservation (77).
The use of EOs as natural preservatives in food industries meets the current consumer trends of “green”,
“biological”, “natural” and “no chemicals added” labels. However, their organoleptic impact must be assessed in each
product, since the concentrations needed to obtain the desired antimicrobial effect might be negatively perceived by
consumers. For example, Viuda-Martos et al. (71) reported a marked aroma of oregano in bologna sausages, which
however was not considered unpleasant by the panellists. Likewise, other authors described the use of oregano EO in a
Spanish fermented dry-cured salchichón, which did not significantly affect sensory properties, but improved texture,
with the consequent possible reduction in the ripening time (78). Furthermore, the addition of rosemary or marjoram
EOs at a concentration of 200 mg/kg in beef patties has been shown to reduce lipid oxidation, due to the EOs’
antioxidant properties, thus improving the flavour of the patties (79). Similarly good acceptance has been reported for
foal meat after 10 days active packaging with 2% oregano EO, due to reduced lipid oxidation shown by lower TBARS
values (80).
The references to recommended concentrations in food products are scarce in the literature, but Dussault and
colleagues (70) have proposed a 5000 ppm limit.
Furthermore, the legal regulations for food additives consider EOs as flavouring agents (81). Rosemary extract is the
only one included in EC Regulation No. 1333/2008 with a legal limit of 100 mg/kg for dry-cured meat products (81).
The combined use of different EOs, in lower concentrations, may satisfy the safety of food products not depreciating
their sensory characteristics (10).
A mixture of cinnamon and clove EOs was found to have a good potential to inhibit growth of spoilage fungi, yeasts
and bacteria usually found on intermediate moisture foods (aW between 0.65 and 0.90), and thus seems to be an
interesting alternative to chemical preservatives well suited to be used in active packaging systems (82).
An active packaging system for chicken meat with 4% rosemary EO has been shown to inhibit the increase of
biogenic amines, namely putrescine, cadaverine and histamine, as well as enterobacteria, Pseudomonas spp. and
Brochothrix thermosphacta involved in their production (83).
Combined use of EOs and starter cultures in the manufacture of traditional Chinese smoked horsemeat sausages
showed that both EOs (cinnamon, cloves, ginger and anise) and starter cultures (L. sakei and S. xylosus) inhibited the
accumulation of biogenic amines, namely tryptamine, putrescine, cadaverine, histamine and tyramine, and the growth of
enterobacteria. It is noteworthy that the inhibitory effects of EOs were stronger than those of starter cultures.
Additionally, the synergistic effects between EOs and starter cultures against the accumulation of the
abovementioned biogenic amines and the growth of enterobacteria were observed (84).
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4.2 Cheeses
The antimicrobial efficacy of the different EOs in dairy products can be influenced by several factors, such as the
chemical composition of these products, the concentration in which the oils are used and the microorganisms that are
intended to be reduced or eliminated.
Comparing the anti-microbial effect of clove, cinnamon, bay and thyme EOs in different concentrations (0.1%, 0.5%
and 1%) in low-fat and full-fat soft cheese, Smith-Palmer et al. (85) found that 1% was the most effective concentration
for all EOs. The anti-Listeria monocytogenes effect was more pronounced in the low-fat cheese, but clove EO at 1%
was more effective in the two types of cheese. This essential oil, at the same concentration, was more active against
Salmonella Enteritidis in full-fat cheese than in low-fat cheese. When used at a concentration of 0.5%, the population of
Salmonella Enteritidis recovered in the low-fat cheese, but not in full-fat cheese.
In fact, fat plays a protective role of the bacterial cells over antimicrobial agents. However, the protein content is
higher in low-fat cheeses and can contribute to the reduction of the activity of the EOs due to the formation of
complexes between the phenolic compounds of the EOs and the proteins of these products (67).
Govaris et al. (86) noted that the antimicrobial activity of oregano and thyme EOs was equivalent for L.
monocytogenes and Escherichia coli O157: H7 in Feta cheese. However, they observed that L. monocytogenes reduced
faster than E. coli O157: H7, most likely because the EOs have a more pronounced effect on Gram-positive than on
Gram-negative bacteria (11).
This may have other consequences, for example in product safety, in processing and conservation phenomena, since
the predominant microbiota, as well as starter cultures, are mostly made up of Gram-positive bacteria.
EOs can increase the shelf-life of dairy products, not only eliminating unwanted microorganisms, but also decreasing
the degree of chemical deterioration during storage and marketing periods.
The addition of oregano and rosemary EOs has affected the number of mesophilic microorganisms in cream cheese.
This occurrence caused a lower pH reduction and a less pronounced acidity. In addition, the rancid and fermented
flavours which determined a shorter shelf-life of the product, were less pronounced in products with added oregano and
rosemary EOs, since the oxidative and fermentative processes were inhibited (36, 87).
The addition of marjoram and rosemary EOs has affected the population of mesophilic bacteria in full cream cheese,
which resulted in a lower pH reduction and a less pronounced acidity.
Clove EO (0.5% and 1%) restricted the growth of L. monocytogenes in cheese both at 30 °C and 7 °C (74).
The reduction of the microbial population is also associated with reduced production of biogenic amines in fermented
products. In Gouda cheese added with Zataria multiflora (thyme-like plant) EO, there was a significant reduction in the
production of histamine and tyramine in cheeses with different EO concentrations. These reductions amounted to 44%
and 46% for tyramine and histamine, respectively, with an EO concentration of 0.4%, although the preferred
concentration for the sensory panel was 0.2%. In this case, the reduction of tyramine and histamine was 22% and 29%,
respectively (88).
4.3 Fruits
Fruits and vegetables are perishable products, characterised by a short shelf-life due to weight loss and decay, this one
caused mainly by fungal activity. This is a huge problem for producers, stakeholders and consumers. Part of the
problem has been solved, or at least minimised, using low temperatures throughout the postharvest period, storage and
transportation over long distances. However, the use of low temperatures is insufficient for consumers and commercial
requirements. So a range of complementary techniques are therefore used to extend fruits’ shelf-life, such as Modified
Atmosphere (MAP) and Controlled Atmosphere (CA). Chemical agents have helped controlling pathogens during the
postharvest period, however there are restrictions on their use related to environmental impact and food safety that
should be considered. Thereby, in recent years, there has been a significant increase in research works about postharvest
control of phytopathogens through alternative natural processes, such as the use of EOs from aromatic plants. EOs of
various plant species have been studied, because of their antimicrobial properties, being effective in the control of fungi
first of all in vitro and later on in vivo in vegetables and fruits.
Many research works demonstrated the real effectiveness of EOs action in some diseases’ control. The role of EOs as
well as their use in the active packaging of fruits and other foodstuffs, was considered in several studies (4, 8, 11, 17,
An important systematic work was done by Wilson et al. (96) testing numerous extracts from plants and 49 EOs, that
were evaluated for their antifungal activity against Botrytis cinerea, and among all the EO tested, palmarosa
(Cymbopogon martini), red thyme (Thymus zygis), cinnamon leaf (Cinnamomum zeylanicum) and clove buds (Eugenia
caryophyllata) demonstrated the best results controlling the fungus. The same authors stated that the most frequently
occurring constituents in EOs showing high antifungal activity were D-limonene, cineole, β-myrcene, α-pinene, β-
pinene and camphor.
Recently, Campos et al. (12) using thyme and sage EOs, in strawberries, in the head space of the package, observed
the decreasing in the amount of fungi existing with these treatments, when compared with the control samples. Braga
(97) also tested different EO in strawberry with promising results. Moghaddam et al. (98) presented results that proved
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the effect of the EO of Echinophora platyloba in relation to different fungi, highlighting its great antifungal power.
Feliziani & Romanazzi (99) verified that the presence of some EOs has an effect on some fungi, especially on Botrytis
cinerea. Reminding that this fungus appears very frequently in fruits in the postharvest period. Vitoratos et al. (100)
confirmed the effect of EO of thyme, oregano and lemon with different concentrations, in strawberry, tomato and
cucumber, to evaluate the reduction of propagation of different fungi. Scariot (101) obtained EOs from Mentha
arvensis, Citrus limon, Zingiber officinalis, Thymus vulgaris and tested in vitro and in vivo in strawberries and verified
that all of them would have some effect on the growth of the fungus Botrytis cinerea. Mohammadi et al. (92) tested in
vitro the fungicide effect of four EOs (fennel, black caraway, peppermint and thyme) at five different concentrations
and found that they presented effect on the growth of the fungus Botrytis cinerea and Rhizopus stolonifer.
EOs have been recently used in table grapes, in order to improve shelf-life without changing their organoleptic
characteristics. Several authors tested a new package, with grapes wrapped with two distinct films, with the addition of
a mixture of eugenol, thymol and carvacrol, and observed that microbial counts were drastically decreased as well as
lower occurrence of berry decay (102, 103). Several works on ‘Crimson Seedless’ table grapes, using MAP and
eugenol, thymol or menthol inside the packages, showed that counts for yeasts and moulds were significantly reduced in
the grapes’ packages with natural antimicrobial compounds. Valero et al. (102) tested table grapes on MAP conditions
and active packaging by adding eugenol or thymol and obtained reduced losses of quality, considering sensory,
nutritional and functional properties, and also lower spoilage counts, in active packaging with added EO. According to
Ricardo-Rodrigues et al. (94), ‘Crimson seedless’ table grapes treated with eugenol and menthol EOs had better results
during the storage time compared to grapes without such treatments.
Waithaka et al. (95) tested the controlling effect of EOs against other fungi, like Alternaria spp., Fusarium spp.,
Colletotrichum spp. and Penicillium spp., present in species like Passiflora edulis Sims (Passion fruit). They extracted
EOs from rosemary and eucalyptus (Eucalyptus agglomerata). The main conclusion was that those EOs are capable of
controlling the above referred passion fruits’ fungal pathogens.
The use of edible coatings, like chitosan, combined with EOs, allows the synergetic effect of reducing weight loss
and maintaining overall quality of fruits. Munhuweyi et al. (93) investigated the in vitro and in vivo inhibitory effects of
chitosan EOs, with different concentrations of lemongrass, cinnamon, and oregano oils, using vapour emission and
direct coating against Botrytis sp., Penicillium sp. and Pilidiella granati pathogens of pomegranate fruit. Chitosan film
incorporated with oregano EO had the highest antifungal activity, followed by cinnamon and lemongrass EOs. The
inhibitory effect was higher for fruit directly dipped into the chitosan-EO emulsions than those exposed to vapour.
Recently, the idea of using the potential antimicrobial effect of EOs has served as a basis for the development of
innovative approaches to increase shelf-life of fresh-cut fruits and vegetables, referred to as minimally processed (MP)
products (104), such as the use of EOs in addition to edible films (105). The more enlightened consumers show great
interest in acquiring MP products, "easy to eat", and at the same time seeking to ensure that these products correspond
to the concept of clean label, natural and environmentally "friendly".
5. Conclusions
EOs are natural substances extracted from medicinal and aromatic plants, commonly by distillation processes. These
compounds have an important role in food preservation contributing to safety and shelf-life extension of food products.
The improvement in food safety is due to the inhibition of pathogenic microbial growth and reduction of biogenic
amines, mainly in meat and meat and dairy products, as a consequence of the inhibited growth of spoilage
microorganisms. The extension of food products’ shelf-life results from enzymatic reduction, mainly due to their
antioxidant activity.
The EOs effectiveness is attributed to the presence of phenolic natural compounds and they are an important and
healthy alternative to synthetic preservatives and chemical additives. The FDA treats antimicrobial agents of natural
origin as GRAS type products, including plant products and their EOs.
Driven by the growing interest of consumers for natural ingredients and their concern about potentially harmful
synthetic additives, the global demand for EOs is increasing nowadays, and more than 250 types of EOs are marketed
annually worldwide.
Most EOs are composed of terpenes, and other aromatic and aliphatic constituents with low molecular weights. The
major bioactive fraction (90%) of EOs is composed by monoterpenes. Generally, the EOs with the strongest
antibacterial properties against foodborne pathogens contain a high percentage of phenolic compounds, such as
carvacrol, eugenol and thymol.
The antagonistic effect of the major compounds of EOs are studied against bacteria (B. cereus, E. coli, L.
monocytogenes, Salmonella spp., S. aureus, C. perfringens, among others), moulds (Fusarium spp. and Aspergillus
spp., among others) and yeasts (for example C. albicans).
Besides the richness in nutrients, which increases microbiota resistance to EOs, factors as lipid contents, once EOs
are soluble in lipids, and low aW, that reduces the aqueous phase of food products increasing the contact between EOs
and spoilage or foodborne microbiota, enhances their antimicrobial effect.
Antimicrobial research: Novel bioknowledge and educational programs (A. Méndez-Vilas, Ed.)
However, it must be taken into account that EOs have an intense taste and smell, which can modify the taste and
aroma of food products. Therefore, studies should focus on the minimum necessary EO amount, which still maintains
antimicrobial activity without changing the organoleptic characteristics of food products. Besides, the combined use of
different EOs, in lower concentrations, may satisfy the safety of food products not depreciating their sensory
Acknowledgements This work was funded by National Funds through FCT-Fundação para a Ciência e a Tecnologia under Project
UID/AGR/00115/2013. M. Laranjo acknowledges a Post-Doc research grant from FCT (SFRH/BPD/108802/2015).
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Antimicrobial research: Novel bioknowledge and educational programs (A. Méndez-Vilas, Ed.)
... The most common microorganisms associated with food borne illness are Bacillus cereus, Salmonella spp. Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes (Gustafson & Wilkinson, 2005;Laranjo et al., 2017;Turgis et al., 2012). ...
... Rosemary EOs found to be effective in controlling the growth of Bacillus cereus with a MIC value of 0.2 μl/ml (Burt, 2004;Chaibi et al., 1996;Laranjo et al., 2017). According to different published data accounting for antimicrobial efficacies of EOs reported that clove, sage, oregano, thyme, and rosemary EOs showed appreciable inhibitory effect against the growth of E.coli and accounts for the MIC values ranges from 0.4 to 10 μl/ml (Burt, 2004;Hammer et al., 1999;Laranjo et al., 2017;Smith & Stewart, 1998). ...
... Rosemary EOs found to be effective in controlling the growth of Bacillus cereus with a MIC value of 0.2 μl/ml (Burt, 2004;Chaibi et al., 1996;Laranjo et al., 2017). According to different published data accounting for antimicrobial efficacies of EOs reported that clove, sage, oregano, thyme, and rosemary EOs showed appreciable inhibitory effect against the growth of E.coli and accounts for the MIC values ranges from 0.4 to 10 μl/ml (Burt, 2004;Hammer et al., 1999;Laranjo et al., 2017;Smith & Stewart, 1998). Various studies have reported the inhibitory effect of EOs obtained from oregano, sage, rosemary, clove, and thyme against S. aureus growth with MIC values accounting from 0.2 to 10 μl/ml (Burt, 2004;Cosentino et al., 1999;Hammer et al., 1999;Laranjo et al., 2017;Smith & Stewart, 1998). ...
According to the definition given in literature, essential oils (EOs) are defined as an aromatic volatile fraction isolated from different parts of plants such as leaves, fruits, bark etc using different extraction processes. They are synthesized by all plant parts and are principally complex mixture of terpenes and their oxygenated derivatives. Due to their antimicrobial properties, now they are representing an interesting source of natural antimicrobials for food preservation. The side effects caused by synthetic preservatives have pushed the scientific community to find an alternative that covers the same antimicrobial efficacies without affecting the organoleptic properties of food products and supports the trend of green consumerism. In this search, essential oils became a potent candidate in food preservation and now‐a‐days, play momentous role in food preservation. This review noticeably focuses on the applications of EOs as food preservatives along with the current prospects and limitations.
... These dyes are widely used as colorants in processed foods and beverages. Most often it can be found in burgers, sausages, red alcohols, soft drinks, sweets, and fruit yogurts [10][11][12][13]. ...
... However, this is not their only advantage. These types of substances can provide additional health benefits since they are very often bioactive compounds with antioxidant properties [9,10,12,13]. ...
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These days, consumers are increasingly "nutritionally aware". The trend of "clean label" is gaining momentum. Synthetic additives and preservatives, as well as natural ones, bearing the E symbol are more often perceived negatively. For this reason, substances of natural origin are sought tfor replacing them. Essential oils can be such substances. However, the wider use of essential oils in the food industry is severely limited. This is because these substances are highly sensitive to light, oxygen, and temperature. This creates problems with their processing and storage. In addition, they have a strong smell and taste, which makes them unacceptable when added to the product. The solution to this situation seems to be microencapsulation through complex coacervation. To reduce the loss of essential oils and the undesirable chemical changes that may occur during their spray drying-the most commonly used method-complex coacervation seems to be an interesting alternative. This article collects information on the limitations of the use of essential oils in food and proposes a solution through complex coacervation with plant proteins and chia mucilage.
... Eos can be widely used in the preservation of fruits due to its efficient antibacterial and antioxidant properties (Laranjo et al., 2017). ...
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Fruits are highly susceptible to postharvest losses induced majorly by postharvest diseases. Peach are favored by consumers because of their high nutritional value and delicious taste. However, it was easy to be affected by fungal infection. The current effective method to control postharvest diseases of fruits is to use chemical fungicides, but these chemicals may cause adverse effects on human health and the residual was potentially harmful to nature and the environment. So, it is especially important to develop safe, non‐toxic, and highly effective strategies for the preservation of the fruits. Essential oil, as a class of the natural bacterial inhibitor, has been proven to exhibit strong antibacterial activity, low toxicity, environmental friendliness, and induce fruit resistance to microorganism, which could be recognized as one of the alternatives to chemical fungicides. This paper reviews the research progress of essential oils (Eos) in the storage and preservation of fruits, especially the application in peach, as well as the application in active packaging such as edible coatings, microcapsules, and electrospinning loading. Electrospinning can prepare a variety of nanofibers from different viscoelastic polymer solutions, and has broad application prospects. The paper especially summarizes the application of the new Eos technology on peach. The essential oil with thymol, eugenol, and carvacrol as the main components has a better inhibitory effect on the postharvest disease of peaches, and can be further applied. Practical applications As an environmentally friendly natural antibacterial agent, essential oil can be used as a substitute for chemical preservatives to keep fruits fresh. This paper summarizes the different preservation methods of essential oils for fruits, and especially summarizes the different preservation methods of essential oils for peaches after harvesting, as well as their inhibitory effects on pathogenic fungi. It could provide ideas for preservation of fruits and vegetables by essential oils.
... Among its multiple components, EOs have several that have antiviral, antifungal, antitoxigenic, antiparasitic, and insecticidal activity, which may be related to the protective function that these substances have in the plant (Abbaszadeh et al., 2014;Laranjo et al., 2019). In spices, phenolic compounds are probably the main active components of their EOs (López-Malo et al., 2002), standing out among these carvacrol, eugenol, thymol, p-cymene, γ-terpinene, etc. (Zeid et al., 2019;Laranjo et al., 2017). Therefore, new alternatives based on cinnamon, clove, ruda, and other plants, have been studied as shown in Table 1. ...
Berries have wide market possibilities in the fruit sector although they have a short shelf life, which is why it is necessary to improve the existing packaging and storage systems. Given the need to increase the shelf life of berries reducing factors causing deterioration such as fungal decay, in this review the effect and application of different plant‐based natural antimicrobial agents is described focusing on their use in active packaging for berries and fruits of similar size. The most used components are mentioned recognizing the packaging material, application mode and target microorganism, besides, the microbiological technique. Botrytis cinerea was the most reported mold. Molds and yeasts count, minimum inhibitory concentration (MIC) and disc diffusion method were the most used techniques. According to the reviewed literature, these natural compounds show promising results for molds inhibition, and their use in active antimicrobial packaging to increase shelf life for these fruits.
... Because of its high volatility, ephemerality, and biodegradability, essential oils are well accepted by consumers (Bakkali et al. 2008;Falleh et al. 2020). For example, Mediterranean food products like meat and products, preserved with essential oils are well liked and of added value products by consumers (Laranjo et al. 2017). However, there are some lacunas in the use of essential oils as food preservatives at industrial level such as less water solubility, strong distinctive aroma, less stability etc. ...
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Essential oils, also called volatile odoriferous oil, are aromatic and volatile liquids extracted from different parts of plants by steam distillation, dry distillation, hydro-diffusion, or other suitable mechanical methods without heating. Essential oils and their constituents have wide range of applications in the field of pharmaceutical, sanitary, cosmetic, agricultural, and food industries as they are safe, eco-friendly, easily degradable, cost-effective and renewable source. Due to negative side effects of synthetic preservatives, the uses of essential oils have received increasing interest as the natural additives for the shelf-life extension and preservation of food products. Food preservatives are mainly classified into two main groups: antioxidants and antimicrobials. Antioxidants are compounds that delay or prevent the deterioration of foods by oxidative mechanisms. Antimicrobial agents inhibit the growth of pathogenic microorganisms in food. This chapter is mainly focussing on the various food preservative properties of essential oils with special reference to their antioxidant activities.
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The aim of this work was to compare the chemical composition and antioxidant activity of the essential oils from two plant parts (leaves and stems) of fennel, wild-grown in the Montenegro seaside. The chemical composition of the isolated essential oils was determined by gas chromatography with mass spectrometry (GC/MS) and flame ionization detection (GC/FID). The yield of the fennel essential oils (FEOs) from leaves (0.83%) was four times higher than that from the fennel stems (0.21%). Forty-six compounds were identified from leaves’ FEOs and were mainly aromatic compounds (68.5%), monoterpenes (17.8%), and others, where the most abundant compounds were (E)-anethole (51.4%) and methyl chavicol (9.3%). Forty-seven compounds were identified in the FEOs from stems, which were mainly aromatic compounds (69.7%), oxygen-containing monoterpenes (14.9%), where the most abundant compounds were also (E)-anethole (55.7%) and methyl chavicol (7.8%). The FEOs from stems showed higher antioxidant activity, with an EC50 value of 2.58 mg/mL, than in the fennel leaves, which had an EC50 value of 6.91 mg/mL. The FEOs show superior antimicrobial activity against Candida albicans (45.3 mm) and Bacillus subtilis (24.0 mm). Isolated essential oils could be used as a safer alternative to synthetic additives in the food industry.
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Awareness about pollution worldwide through the excessive use of chemicals that affect every part of our environment makes the urgent need to use natural alternatives eco-friendly materials to reduce the losses come from synthetic chemicals. In recent decades, a great leap has been made to control weed by synthetic herbicides which are considered the most effective weed control method in comparison with the other methods. Although synthetic herbicides are considered less toxic between other pesticides such as insecticides and fungicides, the usual use, even if it is used at the recommended rates harmed the environment and human health. Previous works indicated that Essential oils have been demonstrated to have good phytotoxic activity on various plant species by suppressing germination and reducing growth parameters. Phytotoxic activity of essential oils can act directly as bioherbicide by effects on one or more than one of the biological processes inside plants which cause the death of plant completely or partially. This chapter highlights the desirable phytotoxic activity of essential oils and their possible uses as natural weed killers.KeywordsAllelopathyEssential oilsPhytotoxic activitySynthetic herbicidesNatural weed killer
The application of essential oils in the food sector as a flavor enhancer has been known. Essential oils are secondary metabolites that are volatile and have a sharp and strong aroma. The constituent components of essential oils consist of terpenes, terpenoids, phenylpropanoids, and various compounds of low molecular weight. Research on essential oils proves that essential oils have antimicrobial and antioxidant properties. The positive impacts of the use of Essential oils in food have the potential to be used as natural food preservatives and food safety. Essential oils can be used as a substitute for chemical preservatives with a “green” label because they are known as Generally Recognized as Safe (GRAS). The negative impacts of using essential oils in food include a sharp and strong aroma that may be disliked in food. This is also related to the dose required if it is used as a preservative or food safety, in that dose the strong aroma of essential oil may not be organoleptically acceptable. In addition, essential oils are also unstable to high temperatures, light, air and moisture.KeywordsEssential OilAntimicrobialAntifungalAntivirusAntioxidantNatural PreservativeFood SafetyFood Flavor AgentPositive Impact of Essential OilNegative Impact of Essential Oil
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Fungi are organisms that feed from organic matter and act as parasites in living organisms. They are found in different environments and their growth in food products has become a global concern, as well as the resistance to commercial fungicides, due to the economic damage generated by food deterioration and the harmful effects on human health. Thus, the search for new natural fungicides has increased, such as essential oils from plants that have been promising in combating fungi, improving the quantity and quality of foods with low toxicity. This chapter aimed to carry out a bibliographical review on promising essential oils in combating fungal species of the genera Aspergillus, Penicillium, Fusarium, Alternaria, Candida and Cladosporium, the main food spoilage, and their constituents.KeywordsFungiFoodDeteriorationEssential oil Aspergillus Penicillium Fusarium Alternaria Candida Cladosporium
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Essential oils are chemical substances composed mainly of terpenes and terpenoids. These compounds are widely investigated due to their lipophilic characteristics and biological and pharmacological properties. Therefore, the objective of this review was to investigate the potential of essential oils against species of the genus Leishmania, parasites causing the infectious disease leishmaniasis. Using the descriptors “Essential oil AND Leishmania” information available in the Scopus© database was collected. 114 articles met the inclusion criteria and were selected for analysis in this study. Among the tests performed, most were of the in vitro type (97.4%) and L. amazonensis (47.4%) and L. infantum (28.9%) were the species most used in these studies. Among the studies that investigated the mechanism of action, the essential oil of the species Tetradenia riparia showed the best result of IC50 (0.03μg/mL) against L. amazonensis isolates. Several works attribute the anti-Leishmania activities of essential oils with different bioactivities, such as: morphological and immunological alterations, antioxidant capacity and enzymatic action. Finally, it is concluded that essential oils have great potential for the development of new drugs against leishmaniasis, however further research is needed through in vivo tests to elucidate the mechanisms of action of such compounds.KeywordsLeishamaniasisTerpenesTerpernoidsMedicinal plantAnthropozoonosisMonoterpenesSesquiterpenes Lutzomyia Phlebotomus Mechanisms of action
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Growth of fruits which form an important part of human diet has been jeopardized by the many fungal diseases that are present today. This study was conceived to isolate the most common fungal pathogens in passion fruits. Fungi were isolated using potato dextrose agar in addition to characterization using morphological, cultural, and biochemical means. Extraction of essential oils from rosemary (Rosmarinus officinalis) and eucalyptus (Eucalyptus agglomerata) was done. Before carrying the sensitivity test of essential oils to the fungal isolates, constituents of the essential oils were determined.The most common fungal pathogens isolated from passion fruits were Alternaria spp. (45%), Fusarium spp. (22%), Colletotrichum spp. (17%), and Penicillium spp. (16%).There was a relationship between heating time and yield of essential oils in rosemary (𝑟 = 0.99) and eucalyptus (𝑟 = 0.99). Conversely, there was no significant difference in the amount of essential oils produced by rosemary and eucalyptus (𝑃 = 0.08). Furthermore, there was a significant difference in growth inhibition of the fungal pathogens between essential oils fromrosemary and eucalyptus (𝑃 = 0.000438). Fungal pathogens isolated frompassion fruits can be controlled using essential oils fromrosemary and eucalyptus. The oils need to be produced in large scale.
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Nos últimos anos, a cultura do morango tem vindo a assumir uma maior importância devido ao seu potencial de exportação e à elevada procura que se verifica, mas a sua curta vida útil dificulta a sua comercialização.
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A wide range of medicinal and aromatic plants (MAPs) have been explored for their essential oils in the past few decades. Essential oils are complex volatile compounds, synthesized naturally in different plant parts during the process of secondary metabolism. Essential oils have great potential in the field of biomedicine as they effectively destroy several bacterial, fungal, and viral pathogens. The presence of different types of aldehydes, phenolics, terpenes, and other antimicrobial compounds means that the essential oils are effective against a diverse range of pathogens. The reactivity of essential oils depends upon the nature, composition, and orientation of its functional groups. The aim of this article is to review the antimicrobial potential of essential oils secreted from MAPs and their possible mechanisms of action against human pathogens. This comprehensive review will benefit researchers who wish to explore the potential of essential oils in the development of novel broad-spectrum key molecules against a broad range of drug-resistant pathogenic microbes.
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Antimicrobial substances may be synthetic, semisynthetic, or of natural origin (i.e., from plants and animals). Antimicrobials are considered " miracle drugs " and can determine if an infected patient/animal recovers or dies. However, the misuse of antimicrobials has led to the development of multi-drug-resistant bacteria, which is one of the greatest challenges for healthcare practitioners and is a significant global threat. The major concern with the development of antimicrobial resistance is the spread of resistant organisms. The replacement of conventional antimicrobials by new technology to counteract antimicrobial resistance is ongoing. Nanotechnology-driven innovations provide hope for patients and practitioners in overcoming the problem of drug resistance. Nanomaterials have tremendous potential in both the medical and veterinary fields. Several nanostructures comprising metallic particles have been developed to counteract microbial pathogens. The effectiveness of nanoparticles (NPs) depends on the interaction between the microorganism and the NPs. The development of effective nanomaterials requires in-depth knowledge of the physicochemical properties of NPs and the biological aspects of microorganisms. However, the risks associated with using NPs in healthcare need to be addressed. The present review highlights the antimicrobial effects of various nanomaterials and their potential advantages, drawbacks, or side effects. In addition, this comprehensive information may be useful in the discovery of broad-spectrum antimicrobial drugs for use against multi-drug-resistant microbial pathogens in the near future.
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Many food products are perishable by nature and require protection from spoilage during their preparation, storage and distribution. The food products are now often sold in areas of the world far distant from their production sites, and hence need for extended shelf-life products has increased. Several food preservation systems including addition of antimicrobial compounds can be used to enhance shelf-life and reduce the risk of food poisoning. The most common classical preservative agents are the weak organic acids and sodium chloride. However, negative perception against artificial synthetic chemicals has shifted effort towards the development of alternatives that consumers perceive as ‗naturals‘. Spices and herbs can enhance shelf-life because of their antimicrobial nature, which are primarily added to change or improve taste. Their components are known to contribute to the self-defense of plants against infectious organisms. Therefore, use of essential oils (EOs) of spices and herbs present a better choice than synthetic chemical additives, especially for ―organic‖ food production, which has become popular and is widely accepted by consumers. K e y w o r d s Food preservation, antimicrobial compound, essential oil.
The antimicrobial activity against Escherichia coli and Listeria innocua of nanoemulsions containing oregano, thyme, lemongrass or mandarin essential oils and high methoxyl pectin was assessed during a long-term storage period (56 days). On one hand, a higher antimicrobial activity was detected against E. coli compared to L. innocua regardless the EO type. Transmission Electron Microscopy (TEM) images showed a significant damage in the E. coli cells for both the cytoplasm and cytoplasmic membrane, led to cell death. The antimicrobial activity of the nanoemulsions was found to be strongly related to the EO type rather than to their droplet size. The lemongrass-pectin nanoemulsion had the smallest droplet size (11 ± 1 nm) and higher antimicrobial activity reaching 5.9 log reductions of the E. coli population. Nevertheless, the freshly made oregano, thyme and mandarin EO-pectin nanoemulsion led to 2.2, 2.1 or 1.9 E. coli log-reductions, respectively. However, the antimicrobial activity decreased significantly during storage regardless the EO type, which was related to the loss of volatile compounds over time according to our results. The current work provides valuable information in order to make progress in the use of nanoemulsions containing EOs as decontaminating agents in food products.
Antibiotics have been used for decades in poultry diets to increase performance and decrease morbidity and mortality. The growing concern over the spreading of antibiotic-resistant bacteria among animals and humans has resulted in the ban of the feed use of antibiotic growth promoters in livestock and in some cases additives derived from plants are used as alternative. Four commercial essential oils, from litsea (Litsea cubeba (Lour.) Pers.), oregano (Origanum vulgare L. subsp. hirtum), marjoram (Origanum majorana L.), thymus (Thymus vulgaris L.) and their mixtures, were tested against pathogenic bacteria and yeasts that may be shed in faeces by poultry. In particular, the analysis were carried out against reference and wild bacterial strains of Salmonella enterica serovar Typhimurium, Yersinia enterocolitica, Listeria monocytogenes, Enterococcus durans, E. faecalis, and E. faecium, and wild isolates of Candida albicans, C. tropicalis, C. guilliermondii, C. krusei, C. parapsilosis and Saccharomyces cerevisiae. Essential oils had varying degrees of growth inhibition in relationship to the tested bacterial and yeast strains; however the best results were achieved by O. vulgare and T. vulgaris. All mixtures gave good results with reference and field bacterial strains, with MIC values ranging from 1.13 to 0.14 mg/ml. The mixture composed by O. vulgare, T. vulgaris and O. majorana appeared the most effective against the tested yeast isolates, with MIC 1.85 mg/ml. O. vulgare and T. vulgaris showed good antimicrobial activities, thus they seem useful not only to promote poultry growth, but also to control fastidious microorganisms commonly occurring in digestive tract of these animals.