Intrinsic and Extrinsic Factors of Essential Oil Quality
Brian M. Lawrence, PhD
To understand how growing conditions and plant material affect the quality of essential oils, one must first understand what is meant by the term quality. Quality is a measure of the non-controllable and controllable factors surrounding the growth, harvesting, and processing of plants used for essential oils. Quality informs the user that the product possesses standardized, distinctive, perceptual, and distinguishing attributes that convey excellence and superiority.
To attain quality in a product like an essential oil, quality control measures are carefully planned and continually verified using a set of quantitative and qualitative procedures. To ensure that each essential oil sold meets this high standard of quality, a process called quality assurance is used to determine that each essential oil will perform its intended purpose. The quality and composition of essential oils are dependent on intrinsic and extrinsic factors. Intrinsic factors are the occurrences within a plant that determine essential oil composition, such as plant genetics. This includes ploidy (number of pairs of chromosomes), clones, hybrids, cultivar populations, and specific taxon variations.
Intrinsic factors also include ontogenetic characteristics, which are time variable, such as variation in growth, or development stages, of the plant. The life cycle of a member of the plant kingdom is genetically controlled by the need to reproduce. Consequently, anything that the plant can do to ensure the species survival will be done.
Essential oils, also known as secondary metabolites, are produced by some plants as a survival mechanism and for plant support. They are emitted to ensure pollination, to prevent herbivores from grazing, and to help prevent insect, fungal, or bacterial infestation. Secondary metabolites are not specific to the growth of the plant, but they aid in transport and transitional consumption of nutrients, water, and trace elements to support the plant’s life cycle.
Secondary metabolites are found in cutaneous or subcutaneous glands or ducts that exist throughout the plant’s life cycle irrespective of whether it is an annual or a perennial. These glands can be found in various organs of the plant; however, generally they are maximized in one organ, such as the inflorescence (flower) or its calyx, the leaf, bud, root or rhizome, or in the case of some trees, the heartwood or the oleo-gum-resin that exudes from the trunk of a limited number of trees when wounded. The production of secondary metabolites could be considered a concentrated storage of carbon (the lifeblood of a living organism). It can be converted into a glycoside and transported for energy needs within the plant.
Intrinsic factors are not always controllable, but they can be accounted for by regulating how much of a plant is harvested, which plant variations are grown, and what plant part to plant part ratios are used (e.g., leaf:stem, flower:leaf) A good example of this is Clary Sage. If we examine the oil content of its various plant parts, the main oil content can be found in the calyx (0.5–1.20%). The oil content of other parts of the plant are stems (0.002–0.006%), leaves (0.002–0.15%) flower spikes (0.11–0.20%), and new buds (0.04–0.09%). The oil content for the whole, above-ground plant is 0.06–0.30%. As is apparent, the oil composition of the leaves and stems is different to that of the flower spikes, buds, and calyces. Consequently, the leaf and stem ratio to the floral parts affects the oil composition. Other endogenous factors such as insect, fungal, or bacterial damage to the plants harvested will affect the oil composition as well.
In contrast, extrinsic factors are all the factors outside the plant that can affect the quality of essential oil produced. This includes diurnal and seasonal sunlight, temperature, rainfall, wind, pressure, soil, nutrients, and water availability. Essential oil bearing plants can be found throughout the world from temperate to tropical regions. Some plants are endemic (unique) or specific to an island, country, or specific micro-climate. Other plants are known as indigenous or native (occur naturally) or have developed in an ecosystem but can be found elsewhere around the world. Finally, there are alien plants, which are plants that have been introduced to an area where they can be found growing (wild plants) or are cultivated. Despite this variety, extrinsic factors are largely controllable because of agricultural advancements and because of doTERRA’s Co-Impact Sourcing® initiative. Extrinsic factors also include the harvesting and processing of essential oils. This includes the dryness of the plants, the distillation method used, and the age and storage conditions of the oil once it is produced.
There are approximately 350,000 plant species known, of which 17,500 are aromatic in nature, from which essential oils can be produced. Each of these plants has different intrinsic and extrinsic factors that determine its essential oil quality. doTERRA closely monitors the growth, harvesting, and processing of all their plants to ensure that only quality-assured essential oils are produced.