84 NATURALS
fraction contains phenols and sterols that show multiple bioactivities, as antimicrobial, antioxidant, antitumoral or anti-free-radical properties, among others. Liposoluble vitamins are also naturally present, mainly vitamins A (retinol) and E (tocopherol) at small proportions.
Quality
Besides fatty acid profile, to assess quality of a vegetable oil and fitness to be incorporated in a cosmetic formulation, there are also other parameters that must be analysed, as density, absorbance, refractive index, peroxide index, acidity, saponification value or moisture, among others. Another fundamental aspect of quality of plant oils is control of lipid oxidation, since this is one of the main causes of damage, given that it affects sensory traits and notably reduces its utility. A great variety of methods have been developed to evaluate resistance to oxidation of vegetable oils, all of them making use of high temperature, in order to study behaviour of oils in forced conditions. Hence, an accelerated ageing is mimicked, intentionally causing oxidation of fatty acids, to delimit the shelf life period of an oil (considering other factors altogether).
Categories Two categories of vegetable oils can be distinguished, depending on downstream processing after extraction: virgin or refined. Refining is a treatment to purify the oil, while thoroughly controling colour, odour, acidity and reduction of oxidation. It combines mild physical and chemical processes not altering structure nor composition of lipid compounds, as it preserves, to the greatest extent possible, presence of natural antioxidants, such as tocopherol. By refining, only certain plant compounds responsible
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for some organoleptic properties are removed, resulting in a 100% natural plant oil, free from some minor compounds giving undesired colour and odour. During refining, gums, waxes, phosphatides and non- esterified free fatty acids are also removed. This way, the oil acquires a uniform hue and gets rid of odour that might be considered unpleasant, gaining also functionality and stability. Virgin oils are those obtained only by mechanical means or other physical procedures, under conditions not causing any alteration, generally by first cold pressing. Application of this extraction method without a subsequent refining keeps unsaponifiable fractions virtually intact, preserving bioactive substances with cosmetic benefits, as well as liposoluble vitamins. Organic certified oils can be found
among virgin oils, those obtained with production standards respectful to ecological principles, and further not having undergone a refining treatment. Refined oils holding an organic certification also exist, only if the refining process has been performed conforming to protocols accepted by the certifying body. Organic certifications are issued by accredited entities with international recognition, and some of their agricultural production standards refrain from pesticide use, artificial fertilizers, growth hormones, antibiotics and transgenic organisms.
Essential oils
Among vegetable extracts commonly known as oils, essential oils are usually included, despite the fact they are not truly greasy vegetable oils constituted by triglycerides.
Essential oils are hydrophobic liquids composed of volatile aromatic chemicals, generally obtained by distillation, as they
occur in minimal proportions. In nature, their role is to protect plants from diseases, predator insects or to attract beneficial insects, by means of their intense aroma, characteristic of each botanical species. Essential oils possess an enormous therapeutic potential, with a wide spectrum of biological activities, being also a sort of raw material of great value in a cosmetic formulation. It is fundamental to remark that essential oils must not be directly used on skin, but diluted in greasy vegetable oils, or in other hydrophobic ingredients as a vehicle, to prevent irritant effects or contact allergy. Standing out among their properties, we find antimicrobial activity – against bacteria, viruses and fungi generally – as well as their antioxidant, antitumoral and anti-free-radical actions. Thanks to these qualities, essential oils offer interesting applications in fields such as pharmacy, aromatherapy or perfumery. They are also used in the food industry (as flavouring agents and/or preservatives).
Advantages Vegetable oils intended for cosmetic formulations provide the final product with naturalness and quality, and thanks to the diversity of their triglyceride and phenolic composition, they offer multiple cosmetic qualities, useful for formulators. Pharmacopeia also considers use of vegetable oils as excipients for active principles, or to improve absorption of lipophilic drugs. In this pharmaceutical compendium, monographies listing conditions and parameters that specific oils must accomplish to be incorporated in a pharmaceutical product can be found. Cosmetic formulations using vegetable oils as the oily phase, besides supplying a valuable source of natural fats and phenolic compounds, offer additional remarkable advantages, such as:
February 2020
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