Essential Oils as Antimicrobial and Food Preservatives

Abstract

Essential oils (EOs) are secondary metabolites produced by aromatic and medicinal plants. These oils have a wide range of applications in the culinary, perfume, antimicrobial and food industries. Because of several reported side effects of synthetic oils, the use of essential oils as antimicrobials and food preservatives is a source of concern. For cereals, grains, pulses, fruits, and vegetables, essential oils have the potential to be employed as a food preservative. When compared to synthetic compounds, EOs derived from safe natural sources and are effective for human health. This chapter will shed light on some medicinal plants that are rich in essential oils, as well as their antimicrobial properties. Because essential oils are rich in a number of active ingredients [e.g., terpenes, terpenoids, carotenoids, coumarins, curcumins] that are important in food industry, they have strong antimicrobial and food preservation. As a result of the diverse properties of essential oils, they can be used in a natural, safe, eco-friendly, cost-effective and renewable manner. Examples of some foodborne diseases will also be highlighted.

1. Introduction

Essential oils [EOs] are a volatile mixture of chemical molecules with a strong odour that is extracted from aromatic and medicinal plants. Steam or hydro-distillation or Soxhlet extraction [solvent extraction or continuous extraction] procedures are used to extract EOs from aromatic and medicinal plants [1]. Essential oil is a liquid that is extracted from flowers, leaves, bark, stems and roots by steam or water distillation. Essential oils are not at all oily-feeling, despite the word ‘oil‘being used. The majority of essential oils are clear, but some, like patchouli, orange and lemongrass, are amber or yellow. They are rich in chemicals like phenols, monoterpenes and ketones. These plant chemicals are called plant ‘essences ‘referring to the fact that they carry some of the plant’s natural ability to resist bacteria and fungi. These are the same chemical molecules that have been isolated or synthesised by the pharmaceutical industry to make drugs.

Commercial antimicrobial treatments had been used to prevent food deterioration or contamination since ancient times. As a result of consumer concerns about synthetic preservatives, natural antimicrobials such as essential oils are receiving more attention. Essential oils and their components from aromatic and medicinal plants had been shown to have antibacterial, antifungal and food preservation properties against a variety of pathogenic microorganisms [2].

Essential oils are hydrophobic liquids of aromatic compounds that are volatile and oily in nature and present in various plant parts such as flowers, leaves bark, stem, root and seed. Many plant essential oils are useful as a flavour or aroma enhancer as food additives. Applications of essential oil that can act as antimicrobial agents are growing due to the broad range of activities, natural origins and are safe. Currently, essential oils are frequently studied for their antibacterial and antifungal [3] as well as for their use as food preservatives [4].

Essential oils are considered to be secondary metabolites and important for plant defence as they often possess antimicrobial properties [5]. The antibacterial properties of secondary metabolites were first evaluated using essential oil vapours [6]. Since then, essential oils or their components had been shown to not only possess broad-range antibacterial and antifungal properties [7, 8].

Wherever you buy essential oils, the quality might vary dramatically from one dealer to the next. Despite the fact that they are all essential oils, they all do not have the same medicinal potential. Furthermore, the price charged does not always reflect the quality of the vendor’s oils. There are a few:

1. CO₂ extracts and absolutes are distilled in different manners.

2. Poor quality oils that have been distilled from poor crops, been handled improperly, are old, etc.

3. Adulterated oils that have chemicals or other oils added to them. These can cause harmful side effects, or at best, provide the only minimal therapeutic benefit of good quality oils.

The information of this chapter was extracted from the accessible international electronic databases [PubMed, Springer, Science Direct, Wiley and Google] and books by keywords were namely: antibacterial, antifungal, bioactivity, essential oils, foodborne disease, food preservative properties.

The major aim of this chapter highlights the use of essential oils and their antibacterial, antifungal and food preservative properties in controlling fungi associated with food commodities. Some food-borne diseases also will be discussed.

2. Essential oils of some medicinal plants

2.1 Lemon essential oil

Lemons are one of the most popular citrus fruits in the world, and they are often used in cooking since they are high in vitamins. It also gives food a pleasing flavour and scent. Lemon oil’s stimulating, soothing, carminative, anti-infection, astringent, detoxifying, antiseptic, disinfecting, sleep-inducing and antifungal characteristics contribute to its health advantages. The antibacterial chemical limonene, which belongs to the terpenes [monoterepenes] group, is found in Lemon essential oil.

Lemon oil [citrus lemon] includes d-lemonene chemicals, which have been researched for their impact on immunological function, lymphatic, circulatory, and digestive systems. It has antibacterial properties and can help white blood cells, phagocytes, and lymphocytes combat infection [9].

2.2 Ginger essential oil

As a member of the Zingiberaceae family, Zingiber officinale Rosc. [ginger] is widely used as a spice or medicinal plant in folk and traditional medicine. Rhizomes, the therapeutic portion of ginger, are utilised in traditional medicine to cure a variety of diseases [10]. It is a volatile substance extracted by distillation of unpeeled rhizome of Z. officinale Roscoe plant. The essential oil of ginger has a strong, warm and spicy aroma. Its colour is clear to light amber, and its consistency becomes thicker with age and exposure to air. Z. officinale is well known for its medicinal and culinary properties. As turmeric and cardamom, ginger also belongs to the family of Zingiberaceae.

Neroli, clove, black pepper, rose [Rosa alba], turmeric, angelica, spikenard, cardamom, clary sage, sweet marjoram, fennel, jasmine, grapefruit, coriander seed, lemongrass Analgesic, antibacterial, anti-emetic, anti-inflammatory, antioxidant, antispasmodic, antitussive, aperitif, aphrodisiac, deputative, stimulant, laxative, febrifuge, digestive, expectorant, immune-modulatory, rubefacient, stomachic and sudorific qualities are all found in ginger oil [11].

2.3 Peppermint essential oil

When dispersed in the air, peppermint is one of the most effective essential oils for destroying respiratory tract pathogens. It works well as a topical application as well. Peppermint menthol is increasingly commonly found in sports creams and chest rubs, such as Halls Mentholyptus cough drops. Although the oil is effective at opening sinus passages, it should be used with caution in this regard.

Peppermint oil should be a part of every traveller’s first aid kit. It can work wonders for motion sickness and general nausea for some people. An excellent digestive tonic, peppermint essential oil can soothe many stomach complaints. For the traveller, its effectiveness in calming motion sickness can be of great help.

In addition, Peppermint oil had been demonstrated to be useful in lowering the symptoms of irritable bowel syndrome, a painful disorder of the intestines, in at least eight controlled investigations. Peppermint is deliciously stimulating to the mind, brightening and sharpening mental attention in addition to supporting the digestive system.

With all of these additional advantages, peppermint is an effective anti-microbial [12].

2.4 Rosemary

Rosemary (Rosmarinus officinal is L.) is a valuable essential oil plant from the Lamiaceae family. According to the evidence found by anthropologists and archaeologists, rosemary, was used in medicine and food industry [13].

Rosemary is a popular spice and medicinal herb all over the world. Rosemary is usually regarded as one of the spices with the highest antioxidant capacity among natural antioxidants. Rosemary essential oils have antibacterial and antifungal properties. It is often used as a food preservative and condiment [14].

2.5 Thyme

Thymol is a natural volatile monoterpenoid phenol that is the main active ingredient of oil extracted from species Thymus vulgaris L., commonly known as thyme, and other plants such as Ocimum gratissimum L. and Origanum spp. L. Thyme Oil is one of the most antiseptic essential oils and is high in antioxidant rating. Thymol, a potent antibacterial, is the primary component of thyme oil. Aromatherapists are well aware that thyme essential oil is one of the most powerful antibacterial essential oils available. Thymol’s antibacterial and antifungal properties had been well reported [15].

Thyme essential oils showed some of the strongest killing power against antibiotic-resistant bacteria, according to studies at the Western Infirmary, Glasgow, UK. Thyme oil kills the anthrax bacillus, the typhoid bacillus, meningococcus and the agent responsible for tuberculosis and is active against Salmonella and Staphylococcus bacteria.

2.6 Clove essential oil

Syzygium aromaticum L. is a member of the Myrtaceae family, which includes the myrtle, Eucalyptus and guava families, and has around 3000 species and 130–150 genera. Clove is a fragrant flower that is grown in Madagascar, Sri Lanka, Indonesia and China [16].

Clove may also be referred to as Clove Tree, Clove Bud, Clove Stem, Tropical Myrtle, Zanzibar Redhead, Cengkih, Chengkeh, Chingkeh. It is typically processed using steam- or hydro-distillation as a method for extracting oil from the flower buds, leaves and stems.

Clove oil comes from the flower buds and leaves of S. aromaticum also known as Eugenia caryophyllata tree. It has a strong spicy scent. It has an analgesic and stimulating effect. Clove stem and leaves essential oils are also available, however, due to its composition and aroma, essential oil produced from the buds is often preferred.

Clove bud essential oil contains up to 85% eugenol, a phenol that contributes significantly to the scent, medicinal effects and safety precautions. Clove buds essential oil also contains a variety of additional compounds, including the sesquiterpene B-caryophyllene, the esters Eugenyl acetate and B-caryophyllene [2].

2.7 Mustard essential oil

Mustard essential oil, which is frequently confused with mustard oil, is distilled from mustard seeds. Mustard essential oil is also known as mustard volatile oil. The essential oil includes 92 percent allyl isothiocyanate, the chemical that gives mustard its strong flavour. This allyl isothiocyanate, as well as key fatty acids including oleic acid, linoleic acid and erucic acid, contribute to mustard essential oil’s lengthy list of medical properties [17].

Over the years, mustard oil had a mixed reputation in many regions of the world. It is utilised as an edible oil there and is believed to be highly healthful, although it is frequently considered poisonous, irritating and unfit for eating in the rest of the globe [18].

Mustard essential oil is one of the most potent essential oils available, and it can be used to cure a variety of diseases. This oil, which is extracted from the black seeds of mustard using the steam distillation method, had a variety of therapeutic characteristics that can help with a variety of health problems [19].

3. Anti-bacterial activity of essential oils

Pathogenic bacteria reduce the quality and quantity by 20–40% of the total harvest every year in grains, seeds, fruits and vegetables during cultivation, transportation and storage. Clavibacter michiganensis, Pseudomonas syringaepv, tomato, Pseudomonas solanacearum, Pseudomonas cichorii. Such bacteria cause substantial losses. There are many essential oils that had been evaluated for their potential for antibacterial activity against these pathogenic bacteria [20].

Gram-negative bacteria are generally more resistant to essential oils than Gram-positive bacteria. Gram-negative bacteria have hydrophilic lipopolysaccharides [LPS] in their outer membranes work as a barrier to macromolecules and hydrophobic chemicals, allowing them to tolerate hydrophobic antimicrobial substances such as those present in essential oils [21].

4. Anti-fungal activity of essential oils

Fungi can degrade food commodities such as grains, seeds, fruits and vegetables by producing mycotoxins, and they can make food unsafe for human consumption by lowering nutritional value [4]. Foodborne fungal infections and their toxic metabolites, according to the FAO, can cause qualitative and quantitative problems. Quantitative losses of up to 25% of total agricultural food commodities throughout the world [21].

Food quality, colour and texture are all reduced as a result of fungal infection in food commodities, as are the nutrients contained and the physiological aspects of food commodities. Fungi can create mycotoxins during infection, which can cause famines in underdeveloped nations [22].

Food contamination by Alternaria, Aspergillus, Penicillium, Fusarium, and Rhizopus spp. is an important issue in terms of moulds because of the associated health risks and foodborne diseases [4].

Essential oils have antifungal properties which are linked to the breakdown of fungal hyphae caused by mono- and sesquiterpene-molecules in the essential oils. Essential oils also increase membrane permeability, which means they can dissolve in cell membranes and produce swelling, limiting membrane function. Furthermore, essential oils’ antifungal effect is due to their lipophilic feature, which allows them to enter cell walls and impact enzymes involved in cell-wall production, causing fungus to change their morphological traits [23].

5. Value of essential oils in food preservation

Essential oils have been successfully used in the preservation of food commodities in order to extend shelf life in recent years. Various researchers have employed essential oils, either in pure or formulation form, to extend the shelf-life of food commodities in a variety of storage containers, including those made of cardboard, tin, glass, polyethylene, or natural textiles, with positive results [4]. Essential oil constituents like citral, citronella, citronellol, eugenol, farnesol, and nerol among others, have been shown to protect chilli seeds and fruits from fungal infection for up to 6 months [24]. Ageratum conyzoides essential oil successfully stopped blue mould from destroying mandarins and extended their shelf life by up to 30 days [4].

Essential oils from Cymbopogon nardus, C. flexuosus and Ocimum basilicum were observed that could significantly control anthracnose in bananas and increased banana shelf-life by up to 21 days. For up to 3 weeks, Cymbopogon flexuosus essential oil [20 L/mL] can preserve Malus pumilo fruits from decaying. The use of Cymbopogon pendulous essential oil as a fumigant increased groundnut shelf-life by 6–12 months [25, 26], thus proving to be more effective than Parkia roxburghii essential oil. These differences in efficacy of essential oils may be related to the use of oils from different plant species, as well as to their chemical composition, dose level, and storage container type [25, 26].

Thyme (Thymus capitate) [0.1%] and Mexican lime (Citrus aurantifolia) [0.5%] oil reduced disease incidence in papaya fruit whereas, cinnamon [0.3%] oil increased banana storage life by up to 28 days and reduced fungal disease incidence in banana [27].

6. Foodborne diseases

The definition of food spoilage can be interpreted as the process in which food deteriorates to the point in which it is not edible to humans, this occurred by many spoilage microorganisms [bacteria and fungi], which by many reactions change the composition of food and deteriorates its texture, odour, colour and taste which make it unfit for human consumption [28].

Food diseases or food spoilage are widespread health problems and a major cause of the reduction in economic productivity and human lives around the world [28]. Food poisoning and spoilage are two different things, which affect the final quality and safety of foods. Food poisoning can be also referred to as food-borne illness. Many different forms of food-borne pathogens, such as bacteria and fungi, cause it when people eat contaminated food. Foodborne infections have become a major problem in the modern world since packaged food consumption has risen dramatically. Pathogens that penetrate packaged foods have a higher chance of surviving, which must be monitored. For this reason, antimicrobial chemicals are applied to food or packaging materials, either alone or in combination [28].

Foodborne infections are caused by pathogenic bacteria, fungus, and parasites infected [29]. Food safety is a well-known problem worldwide. This problem affects hundreds of millions of people who are injured by contaminated or spoiled food. ‘One of the most widespread health concerns and a major cause of productivity loss and bad impact on human health, ‘according to the World Health Organisation [28].

Intoxication, infection and toxic infection are three types of food contamination. Intoxication refers to the production of toxins after ingestion of harmful microorganisms in food; the microbe that produced and excreted the toxic waste products into the food may be killed, but the toxin they produced causes illness or digestive upset; toxic infection refers to the production of toxins after ingestion of harmful microorganisms in food; food infection is the other type of foodborne illness; It is caused by eating food that contains certain types of live microbe which are present in the food, once the food is consumed, the bacterial cells themselves continue to grow and illness can result. Symptoms of food poisoning are headaches, vomiting, nausea, diarrhoea and dehydration, and these symptoms can be out of control which can be fatal many times.

Consumers are increasingly concerned about the rising number of illnesses linked to harmful and spoilage microbes found in food. Food-borne infections affect millions of people every year all over the world, and they can vary from minor irritations to life-threatening conditions. Clinical microbiology laboratories play a critical role in the detection of these illnesses by identifying and reporting infections to public health officials, who then utilise the information to track down food-borne outbreaks [30]. According to the Center for Disease Control and Prevention [CDC], 76 million cases of food-borne disease occur in the United States each year [31]. The case figures are based on reportable disorders that each laboratory is obligated to report to their local or state public health officials, as well as active surveillance undertaken by the Center for Disease Control and Prevention (CDC). Pathogenic E. coli, Campylobacter spp. and Salmonella were the leading causes. Species., although the causes of approximately 80% of illnesses were unknown. Approximately 25% of the 15.9 million gastroenteritis episodes that occur in Australia are thought to be spread by contaminated food. This translates to an average of one foodborne gastroenteritis episode per five years per person [31].

6.1 Pathogens that cause foodborne disease

There were almost 250 distinct food-borne illnesses identified. The majority of these illnesses are infections caused by bacteria, fungus and parasites that can be spread by food. Poisonings, for example, are diseases caused by hazardous poisons or compounds contaminating food, such as toxic mushrooms or fungus. These different diseases have many different symptoms, so there is no one ‘syndrome ‘that is a foodborne illness. However, the microbe or toxin enters the body through the gastrointestinal tract, and often causes the first symptoms there, so nausea, vomiting, abdominal cramps and diarrhoea are common symptoms in many foodborne diseases, and if the symptoms are not controlled lead to be fatal [29].

6.1.1 Listeria monocytogenes

L. monocytogenes is a bacterium that causes food contamination which is responsible for listeriosis. It usually produces just a mild sickness in healthy people. L. monocytogenes can be found all over habitats. It had been isolated from domestic and wild animals, birds, soil, plants, feed, water and food processing factory floors, drains and damp places. This bacterium is a Gram-positive rod-shaped bacterium that do not generate spores. A lot of factors influence the growth and survival of L. monocytogenes [32, 37].

6.1.2 Bacillus subtilis

B. subtilis cells are rod-shaped, Gram-positive bacteria that are naturally found in soil and plants. B. subtilis grow in the mesophilic temperature range. The optimal temperature for growth ranging is 25–35°C. The creation of stress-resistant endospores is one such technique. Another strategy is the uptake of external DNA, which allows the bacteria to adapt by recombination. These solutions, however, take time to implement it can sometimes contaminate food, however, they seldom result in food poisoning, but it main responsible for many types of food spoilage. Several such species have been described which are mostly the variants of B. subtilis, they are probably present in most bread. B. subtilis had been reported spoiling canned seafoods, meats etc. [32].

6.1.3 Micrococcus luteus

M. luteus is a Gram-positive, coccoid bacterium [0.5 to 3.5 microns in diameter]. It is capable of dividing into more than one plane. M. luteus can be found on human skin as well as in soil, dust, water, and air. It is a typical part of the human body’s flora. The bacterium colonises the human mouth, mucosae, oropharynx and upper respiratory tract. It is not usually considered a pathogen, or disease-causing organism of healthy people [33].

6.1.4 Shiga toxin-producing Escherichia coli [STEC]

E. coli are bacteria that form part of the normal gut flora of humans and other warm-blooded animals. Although most E. coli are considered harmless, certain strains can cause severe illness in humans, particularly Shiga toxin-producing E. coli [STEC], which is also known as verocytotoxin-producing E. coli [VTEC]. Infection with STEC is the main cause of haemolytic uraemic syndrome, a condition that can be fatal in humans. E. coli are Gram-negative, rod-shaped bacteria and are members of the family Enterobacteriaceae [34].

6.1.5 Aspergillus flavus

Aspergillus is a common mould found on bread and other types of food such as meat and fish, as the mould grows on food it produces enzymes that break down the food resulting in spoilage. In addition to enzymes, Aspergillus flavus also produce mycotoxins onto the food. Ingestion of mycotoxin-contaminated food is fatal. Hundreds of people in developing countries die every year after consuming grains contaminated with mycotoxins [35].

6.1.6 Rhizopus stolonifera

Rhizopus sp. is a genus of common saprophytic fungi on plants and specialised parasites on animals. The bread mould, Ranunculus stolonifer, may grow on a broad variety of foods and plants, causing food spoilage and plant diseases in the field. It thrives in somewhat acidic environments, thus it like both fruit and bread. Off-flavors, mycotoxins contamination, discoloration, and rotting are all symptoms of food spoilage caused by mould. Spoilage can occur either in the field or in storage. The water activity of the food determines the types of mould spoiling the food [36].

7. Value of essential oils in food preservation

In recent years, there has been successful research into the use of essential oils in the preservation of food commodities in order to extend shelf life. Various investigators had used essential oils, either in pure or formulation forms, to enhance the shelf-life of food commodities in different storage containers such as those made of cardboard, tin, glass, polyethylene, or natural fabrics and have observed significant enhancement of shelf-life [4]. An earlier study reported that some essential oil constituents such as citral, citronella, citronellol, eugenol, farnesol and nerol could protect chilli seeds and fruits from fungal infection for up to 6 months [24]. Essential oil from A. conyzoides successfully controlled the rotting of mandarins by blue mould and increased mandarin shelf-life by up to 30 days [37]. Essential oils from C. nardus, C. flexuosus and O. basilicum and observed that they could significantly control anthracnose in banana and increased banana shelf-life by up to 21 days. For up to 3 weeks, C. flexuosus essential oil [20 L/mL] can prevent Malus pumilo fruits from decaying [26, 38]. A fumigant application of essential oils from Putranjiva roxburghii was effective against A. flavus and A. niger infecting groundnuts during storage and enhanced the shelf-life of groundnut from fungal biodeterioration for up to 6 months [24]. The use of Cymbopogon pendulous essential oil as a fumigant increased groundnut shelf-life by 6–12 months, thus proving to be more effective than P. roxburghii. Food preservation involves preventing the growth of foodborne microorganisms that lead to food spoilage or food contamination just like bacteria, fungi [39]. Unpreserved food can lead to its spoilage by microorganisms which make denaturation to the food and make it unfit to be consumed so the economy of the countries will be affected, or the food can be contaminated by dangerous pathogenic foodborne microorganisms [25, 40].

8. Conclusion

Researchers from all over the world had been drawn to the study of plant antimicrobials as a result of their work on essential oils. Essential oils and their compounds have clearly been extensively characterised, and essential oils had been employed to combat a wide range of diseases. As a result, this chapter included a brief summary of essential oils and how they can be used as antibacterial, antifungal, and food preservatives. Essential oils have a wide spectrum of antibacterial characteristics, according to the relevant literature review and their natural sustainability when they are utilised as possible biocontrol agents against pathogenic bacteria and fungi. In this regard, we suggest that essential oils are safe and cheap as biocontrol products that should be investigated further because of their ability to preserve food.