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Adulteration of Essential Oils

Supply of natural essential oils is limited and the increasing demand for the natural essential oils for use in various industry has led many suppliers to adulterate the natural essential oil in order to increase the supply and lower the prices. It is not uncommon for some suppliers to sell their adulterated essential oils as pure essential oils in the market. These adulterated essential oils may smell like the pure essential oils but they do not have the same therapeutic properties and effect.

In the article, we will discuss the following topics:

  • Essential Oil Standards
  • Standardisation And Adulteration of Essential Oils
  • Unintended Adulteration and Natural Degradation
  • What Lead to Adulteration of Essential Oils
  • Industrial Adulteration of Essential Oils
  • Addition to An Oil
  • Rectification of Essential Oils
  • Reconstitution of an Essential Oil

Essential Oil Standards

To understand how an essential oil may be adulterated, let’s first understand what essential oils are and how essential oils are defined.

Essential oils are aromatic concentrated hydrophobic volatile liquid extracted from plants. According to ISO, essential oils are ‘product obtained from a natural raw material of plant origin, by steam distillation, by mechanical process from the epicarp of citrus fruits, or by dry distillation, after separation of the aqueous phase—if any—by physical process’. Further according to note added to definition by ISO, essential oils can undergo physical treatments such as filtrations, decantation, centrifugation which do not result in any significant change in its composition.

There are no standards for essential oils other than those defined by ISO.


Standardisation and Adulteration of Essential Oils

Standardisation is a process to alter the composition of essential oil to bring its constituents to a given standard. Standardisation should be either carried out in consultation with customer or a customer should know if an essential oil has been standardised.

Standardisation is preferred in case of flavour and fragrance client industries where it is necessary to bring essential oils to a specific composition to eliminate natural variations. Another reason for standardisation may be regulatory requirements. Some essential oils may contain chemicals, classified as toxic, allergic, sensitising or carcinogenic. Hence, it become necessary to treat natural essential oils in order to remove these constituents and meet regulatory requirement.

Adulteration of essential oils on the other hand, happens without the knowledge of customer. Adulteration may or may not be deliberate on part of supplier.


Unintended Adulteration and Natural Degradation

There are many possible reasons for unintended adulteration of essential oils. Some of them may be stem from lack of knowledge and professionalism, wrong selection and treatment of raw material, improper functioning of equipments, and not adopting good manufacturing practices.

Natural alteration or degradation may not be intentional at all by supplier but it is needed to be discussed here to understand how it may lead to poorer quality of essential oil and hydrosol or aromatic waters.

Some essential oils, especially citrus oils, are vulnerable to oxidation on exposure to air, heat and sunlight. Oxidation results in poorer quality stale oil. This is largely caused due to improper storage of essential oils and long shipping periods. The oils should be stored and shipped in cool and dark conditions with no headspace for air in the drums or bottles.


What Lead to Deliberate Adulteration of Essential Oils

Essential oils are expensive and are limited in availability. Suppliers adulterate pure essential oils in order to either meet the increasing demand, increase profitability or meet the prices demanded by client industries.

Price competition in the client industries’ product markets forces suppliers to meet the prices demanded by client industries, which in turn forces suppliers to adulterate the essential oils. The problem is exacerbated by the fact that the prices can change from crop to crop or even from week to week. Variations in the climatic conditions leading to shortage of biomass can lead to price pressure.


Industrial Adulteration of Essential Oils

This is by far the main reason for essential oils losing their purity, thereby making them unfit for therapeutic use.

Essential oils are adulterated on industrial scales to produce standardised oils. As discussed here, no two production of essential oil will produce the same composition of essential oil. This may affect the quality of end product for the client industries and they may require essential oils to be standardised. According to estimates, about 95% of all oils available on the open market are commercially standardised.

In industry terms, when a essential oils is adulterated to improve the fragrance of an oil, it is called ‘bouquetting. And when an essential oil is adulterated to increase its volume with another liquid, its is called ‘cutting’ or ‘stretching’.

There are three basic ways in which essential oils are commercially adulterated:

  • addition to an oil,
  • extraction from an oil
  • simulation (reconstitution) of an oil.

Addition to An Oil

This is the most common type of adulteration in order to produce a standardised profile. In this case, an oil or some other liquid, synthetic or natural in origin, is added to essential oil to meet the standard chemical profile requirement suitable for client industry. The resultant essential oil is a standardised or bouquetted oil.

The three basic types of additions that are possible to produce standardised essential oils are nature-identical, isolate and classical addition.

Nature-identical or Synthetic Addition

In this case, a synthetic aroma-chemical with the same molecular structure and fragrance character as the naturally occurring one is added to an oil. Although sometimes also called ‘natural identical’, these substances are more or less synthetic and are inert and lack bioactivity. This is the most common type of industrial adulteration of essential oils.

Some of the ways in which essential oils are adulterated using this method are:

  • Neroli oil can be adulterated with synthetics such as linalool, nerol, limonene, linalyl acetate and vetiver oil may be supplemented with synthetic such as caryophyllene and derivatives.
  • Low quality lavender oil may be adulterated with linalool and esters, including linalyle acetate, terpenyl propionate among others.
  • Rose oil is added with synthetic such as phenylethylalcohols, diethylphthalate, citronellol, geraniol and others.

Isolate Addition

This is the second most common form of adulteration. In this case, an isolated constituent from another essential oil is added to an oil. Although a natural isolate is added, it may still results in a loss in therapeutic properties of essential oil. It is difficult to detect this adulteration method with gas chromatography and mass spectrometry analysis. Some of the instances where it is used are as follow:

  • Rosemary oil may contain isolates such as limonene, alpha-pinene and camphene from Orange and other monoterpene-rich citrus oils.
  • Black pepper oil may be enhanced with various isolates suchas limonene, phellandrene and pinene and also sesquiterpenes from the cheaper clove oil.
  • Peppermint oil may be enhanced with menthol isolates from cheaper mint oils.

Classical Addition

In this case, one or more cheaper oils are added to a more expensive oil of a similar chemical or fragrance character to increase the quantity and lower the cost of the final product. This method is not much in use nowadays and is used only in cases where isolate or synthetic addition is not feasible and can be detected easily.

As with other cases of addition, classic addition results in either dilution or complete absence of therapeutic properties of the oil. Such end products are a mixture of different genera, species and varieties. These kind of products are not suitable for aromatherapy and may be used for fragrance purposes only.

Some examples of classic additions are as follow:

  • Bulgarian lavender oil is added to expensive French Lavender oil to stretch.
  • Cold-pressed citrus oils are are blended with the distilled versions of these citrus fruits.
  • Rosemary oil can be adulterated with more cost-effective classic additives such as Eucalyptus, White camphor, Turpentine and Spanish sage.
  • Roman camomile oil can easily be stretched with the much cheaper Moroccan wild camomile oil.
  • The higher grades of Ylang ylang, especially Ylang no. 1 and Ylang extra, are diluted with lower grades.
  • Patchouli oil may contain the oils of any number of different genera and species, starting with the inferior Java patchouli, as well as with Chinese patchouli, Gurjun balsam.
  • Clove bud oil is stretched with clove leaf oil since leaves are easier to harvest and clove leaf oils is cheap in comparison to clove bud oil.

Extraction From an Oil – Rectification of Essential Oils

As discussed in the article about how essential oils are extracted, rectification is used to remove constituents from an essential oil to standardise the oil. Rectification lead to changes in therapeutic properties of oil. These kind of oil may or may not be suitable for aromatherapy. Some better known examples of rectification are:

  • Eucalyptus oil is rectified to have terpenes removed to enhance its fragrance character and make it sweeter.
  • Bergamot oil can have its valuable fresh-scented monoterpenes removed to make it softer and sweeter, resulting in an unbalanced, terpeneless Bergamot oil.
  • Thyme ct. thymol oil can have some or all of its valuable thymol removed to make it softer, less irritating to the skin and therefore more industrially useable.

Reconstitution of Essential Oil

This is a method to recreate the fragrance of expensive essential oils or absolutes completely from isolates and synthetic constituents. These kinds of reconstituted oils are used in functional perfumery to lower the cost of production of perfumes.

These kind of oils do not have any kind of therapeutic properties and not to be used in aromatherapy. A reconstituted oil itself can be added to a pure oil, which is another form of classical adulteration. Some examples of reconstitution are:

  • Industrial Lemon oil is made from the constituent citral extracted from Lemongrass or May chang oil, with some d-limonene from Orange oil added.
  • Melissa oil is reconstituted from Citronella, Lemongrass and Lemon.

An essential oil can be adulterated in many ways, some may not be on purpose. However, every kind of adulteration leads to alteration of composition of essential oils. Some adulteration like those due to lack of knowledge and professionalism of distiller are not avoidable; however, some like industrial adulteration should be avoided.

In the next article, we will discuss more about quality of essential oils.

References

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