Safely Store Essential Oils | Stability determinants of storage
In recent years, consumers have developed an ever-increasing interest in natural products as alternatives to artificial additives or synthetics. Among them, essential oils have gained great popularity in the food, cosmetic, household, and pharmaceutical industries. With increased usage, it becomes essential to know certain important factors to prolong the life of our essential oils, with its safe handling, usage, and storage.
Essential oils are known to be susceptible to conversion and degradation reactions over time. Oxidative and polymerization processes may result in a loss of quality and pharmacological properties. Despite their relevance for consumers, there is a scarcity of information available addressing this issue.
We have attempted to draft a few factors affecting the stability of Essential Oils.
Individual essential oils affect differently upon exposure to extrinsic degradation parameters, particularly temperature, light, and oxygen which are recognized to have a crucial impact on essential oil integrity.
Besides organoleptic alterations and viscosity changes, some aged essential oils, as well as oxidized terpenoids, have revealed skin-sensitizing capacities leading to a hypersensitivity reaction, synonymous with allergic contact dermatitis.
Essential Oils have a structural relationship within the same chemical group, which allows them to easily convert into each other by oxidation, isomerization, cyclization, or dehydrogenation reactions, triggered either enzymatically or chemically. Before stability evaluation of essential oils, it should be noted that the chemical composition may already vary in the initial material, being influenced by plant health, growth stage, habitat including climate, the physical, chemical, and biological properties of soil as well as harvest time.
Factors affecting essential oil stability
Degradation of essential oils depends on the chemical, physical and biological properties of soil that influence both the possibility of the essential oil to oxidize as well as the course of the reaction. Therefore, external factors such as temperature, light and accessibility to atmospheric oxygen need to be thoroughly considered. Furthermore, essential oil composition, compound structures, and the presence of impurities may also govern its stability.
Ultraviolet (UV) light and visible (Vis) light are considered to accelerate autoxidation processes by triggering the hydrogen abstraction that results in the formation of alkyl radical monoterpenes have been shown to degrade rapidly under the influence of light. Few oils during storage under the light, lead to the formation of several unidentified minor components. One minor compound in lavender oil yet not further identified broke down when illuminated.
Ambient temperature crucially influences essential oil stability in several respects. Generally, chemical reactions accelerate with increasing heat due to the temperature dependence of the reaction rate. A temperature rise of 10 °C approximately doubles chemical reaction rates.
Both Autoxidation, as well as decomposition of hydroperoxides, advances with increasing temperature, even more so since heat is likely to contribute to the initial formation of free radicals. Contrarily, lower temperatures favor the solubility of oxygen in liquids, which in turn may negatively affect essential oil stability.
As oxidation reactions are among the main causes for the degradation of essential oils, it is obvious that oxygen access plays a decisive role in essential oil stability. Oxygen consumption upon storage of different monoterpenes has been observed, and changes in the composition, as well as physicochemical properties of essential oils, are generally more pronounced in half-filled containers than when only a little or no headspace is present.
Oil oxidation accelerates with the concentration of dissolved oxygen, which in turn depends largely on oxygen partial pressure in the headspace as well as ambient temperature. Without stirring, oxygen diffusion into the sample takes place gradually over time. According to research, oxygen solubility is high at low temperatures and drastically decreases with an increase in temperature.
A recent study revealed the individual character of an essential oil towards oxidation liability. While peroxide formation in oils from rosemary and pine was promoted at room temperature, oxygen solubility seemed to play a more decisive role for the peroxide level present in lavender oil and thyme oil stored at 5 °C. In these oils, the highest POVs were found upon storage in the refrigerator. These findings clarify that the results obtained for one type of essential oil, cannot be transferred to another.
So, we find too much dependability on multiple factors for preserving the quality of any essential oil. Also, any external factor supporting one kind of oil may not support the other. So on a holistic note, we suggest keeping a simple cautionary approach. Store your amber bottle away from light and heat in a cool dark place, preferably in your vanity or bathroom cabinet. And be sure to put the cap back on immediately after use to avoid oxidation and subsequent quality degradation. Practicing this will secure most of your different essential oils for extended qualitative use.