Sea Buckthorn Oil — A Valuable Source for Cosmeceuticals

Sea buckthorn (Hippophae rhamnoides L., Elaeagnaceae.) is a thorny shrub that has small, yellow to dark orange, soft, juicy berries. Due to hydrophilic and lipophilic ingredients, berries have been used as food and medicine. Sea buckthorn (SB) oil derived from berries is a source of valuable ingredients for cosmeceuticals. The unique combination of SB oil ingredients, in qualitative and quantitative aspects, provides multiple benefits of SB oil for internal and external use. Externally, SB oil can be applied in both healthy and damaged skin (burns or skin damage of different etiology), as it has good wound healing properties. Due to the well-balanced content of fatty acids, carotenoids, and vitamins, SB oil may be incorporated in cosmeceuticals for dry, flaky, burned, irritated, or rapidly ageing skin. There have been more than 100 ingredients identified in SB oil, some of which are rare in the plant kingdom (e.g., the ratio of palmitoleic to γ-linolenic acid). This review discusses facts related to the origin and properties of SB oil that make it suitable for cosmeceutical formulation.


Introduction
Sea buckthorn (SB) (Hippophae rhamnoides L.) is a thorny, soil-adhering, deciduous shrub or small tree [1,2].It is naturally found in Northern and Central Europe, Caucasus, and Asia (Siberia, China, and Tibet).Since it has been recognized as a highly valuable plant, SB has been cultivated in different parts of the world, including many countries in Europe, Canada, Russia, and China.[1,3,4].It is an anti-erosive plant that enhances the soil content since its roots have nitrogen-fixing properties [1][2][3].
In natural habitats, it may reach up to 4 m in height [3].
The aim of this review is to discuss the use of sea buckthorn oil, pricipally for cosmetological purposes, in the light of its rich chemical composition.SB oil can be obtained from two parts of the plant-seed or pericarp.Triglycerides, the main constituents of SB oil, due to their fatty acid content (Table 1), are responsible for maintaining the hydration of epidermis by creating an occlusive film on the skin [5,6].

Botanical Features
The name of genus Hippophae comes from two Greek words-"hippo", which means horse, and "phaos", which means to shine; the leaves of this plant were used in ancient times as horse fodder, which gave the horses a shiny coat [3,7].It belongs to the Elaeagnaceae family and should not be mistaken with the buckthorns of the Rhamnaceae family-rhamnus (lat.)means thorny.Sea buckthorn is also known as Siberian pineapple, sandthorn, sallowthorn, and seaberry.[7].
The bark is smooth and sometimes cracked, is either brown or black, and has silvery lines [7,8].The leaves are narrow and lanceolate with silvery-green upper faces covered by hairs underneath.The fruit is a round berry, varying in color from pale yellow or orange to red.The berries ripen in September but may stay on the branches the whole winter.The seed is brown, shiny, and has a smooth surface [3,8,9].The fruit tastes very sour, with a slight bitterness, and has a faint odor [3].
The specificity of this shrub is that it may withstand extremes in temperature, from −43 to +40 • C. It is considered an air-pollution-, drought-and frost-tolerant plant [3,8].Fruit is widely exploited due to its hydrophilic and lipophilic ingredients that are beneficial for human health, but harvesting sea buckthorn fruit is difficult because of the dense thorn arrangement among the berries.The only way to obtain the fruit is often to remove the entire branch of the shrub.This is the reason why berries can be harvested only once every two years [1][2][3].

Methods for Obtaining the SB Oil
SB oil may be extracted in the process of the mechanical cold pressing of seeds, which contain up to 12.5 wt % of oil.The oil is obtained by extraction or in the cold pressing of fruit pulp, which contains 8-12 wt % of oil.The obtained fractions are filtered.The whole process is shown in Figure 1 [10].
The two types of oils differ significantly in terms of appearance and properties.The oil obtained from juicy berries is a thick, dark orange or red-orange liquid with a characteristic smell and a sour taste if it is pressed from the fruit.Both oils contain a wide range of essential unsaturated fatty acids (UFAs), in particular palmitoleic acid (C16:1), which is highly valued in cosmetology.Of all vegetable oils, SB fruit oil has the highest concentration of palmitoleic acid (ω-7) at 30-35 wt %, which is not as high as that of SB seed oil [8].Both oils abound in tocopherols, tocotrienols, and plant sterols.Unlike seed oil, pulp oil has a high concentration of carotenoids [11].Petroleum-ether extraction consistently recovered oils with higher amounts of all analyzed nutritional components [12].Yang and Kallio (2002) suggested that solvent extraction is not suitable for SB oil extraction because harmful solvent residues can be left behind in the extracted oil, which contributes to environmental pollution [13].Aqueous extraction and screw pressing methods are limited by the type of material (seeds vs. pulp) that can be processed, as shown in Table 2 [14].The supercritical CO2 method was flexible in extracting both seed and pulp oils, with relatively high concentrations of all identified nutritional compounds.The addition of co-solvents with CO2 may enhance selectivity for extracting additional nutritional components [12].Petroleum-ether extraction consistently recovered oils with higher amounts of all analyzed nutritional components [12].Yang and Kallio (2002) suggested that solvent extraction is not suitable for SB oil extraction because harmful solvent residues can be left behind in the extracted oil, which contributes to environmental pollution [13].Aqueous extraction and screw pressing methods are limited by the type of material (seeds vs. pulp) that can be processed, as shown in Table 2 [14].The supercritical CO 2 method was flexible in extracting both seed and pulp oils, with relatively high concentrations of all identified nutritional compounds.The addition of co-solvents with CO 2 may enhance selectivity for extracting additional nutritional components [12].

Sea Buckthorn Berries-Chemical Composition
Reports estimate between 100 and 200 ingredients present in the whole plant.Thus, Hippophae rhamnoides has a long history of application as food and medicine [3].
There have been around 14 vitamins identified in sea buckthorn berries, including vitamin A, C, D, E, F, K, P, and B complex vitamins (B 1 , B 2 , B 6 ) [15,16].Vitamin C is present in very high amounts (up to 900 mg%).In comparison with citric fruits, sea buckthorn berries have about a 14-fold higher amount of vitamin C than oranges [17][18][19].The amount of vitamin C is conditioned by the variety of the plant and its geographical location.Sea buckthorn growing in the coastal parts of Europe may contain 120-315 mg% of vitamin C in fresh fruit, while that growing in the Alps may contain up to 405-1100 mg% [19][20][21][22].
The  2005) determined the composition of phenolic acids in several varieties of sea buckthorn berries.Salicylic acid was the principal phenolic acid, accounting for 55-74.3% of the total phenolic acids present.The phenolic acids liberated from esters and glycosidic bonds constituted the majority of the phenolic acids in the berries, whereas the free phenolic acids constituted only up to 2.3% of the total phenolic acids present [27].
Berries are the richest source of lipids.They are located in fruit (the pericarp) or in seed.Both types of fatty oil isolated either from fruits or seeds are rich in liposoluble vitamins and plant sterols [28].Depending on the plant origin, the harvesting time, and the method of oil isolation, the composition of fatty oil from fruits may vary [29,30].Both qualitative and quantitative content of fatty acids (FAs) may differ in SB oil depending if the oil is from fruits or from seeds, being up to 8 wt % from the fruits and up to 12.5 wt % from the seeds [16,17].The concentration of C16 FAs is higher in the pericarp fruit oil, while concentration of C18 FAs is higher in the seed oil [29,30].There have been 8 FAs reported in the pericarp oil: myristic, palmitic, palmitoleic, stearic, oleic, linoleic, arachidic, and α-linolenic acids.Seed oil has two additional acids-lauric and pentadecanoic.Both oils are rich in UFAs, but pericarp oil is richer in monounsaturated fatty acids (MUFAs), while the seed oil is richer in polyunsaturated fatty acids (PUFAs).The quantitative concentrations of palmitic, palmitoleic, and oleic acids in pericarp oil are as follows: 35.2%, 28,5%, and 29.9%, respectively; in the seed oil, quantitative concentrations of oleic, linoleic, and α-linolenic acids are as follows: 23.7%, 37.6%, and 20.5%, respectively [28].

Unsaturated Fatty Acids
UFAs, as colorless liquids with double bonds, are mostly in a cis configuration [8].It was observed that UFAs improve skin structure, appearance and tone by multiple synergistic effects, such as plasma circulation enhancement of necessary nourishment and oxygen to skin, and removal of toxin excess.UFAs exert their effects after reaching deeper skin layers and are converted to prostaglandins [32].
The presence of γ-linolenic acid (GLA) assures the proper transport of nutrients and it is a building material of intracellular cement and skin cell membranes phospholipids [8,29].The lack or insufficiency of GLA may cause skin dryness, rigidity, and susceptibility to lesions.It was observed that skin allergies, inflammations, infections, and the ageing process may be attenuated by the skin penetration of GLA from SB oil [30,32].SB oil has been used as a source of GLA, even in the oral treatment of atopic dermatitis [33].
Linoleic acid (LA), as an ω-6 acid and a constituent of intracellular cement, has been shown to play a role in cellular regeneration and regulation of the skin sebaceous glands function.Supplementation with LA is used in oily and problematic skin care since it unblocks pores and lowers the number of blackheads.A decrease in LA level was observed in patients with acne prone skin [8].The significance of LA and ά-linolenic acid present in SB oil is that these acids cannot be produced by the human body, while other UFAs found in SB oil (GLA, oleic acid, and palmitoleic acid) may in fact be produced by the body under certain conditions [12,31].

Saturated Fatty Acids
Most saturated fatty acids (SFAs) possess straight hydrocarbon chains with an even number of carbon atoms (usually 12-22 carbon atoms) [34].The main function of SFAs in skin metabolism is to provide adequate turgor, firmness, smoothness, and softness of the skin.They enhance a protective barrier role of the skin by an occlusion effect and consequently block transepidermal water loss [5,35].
SFAs present in SB oil are basically nourishing ingredients but may also serve for the stabilization of SB oil, as they prolong its resistance to oxidation [12].

Complex Lipids
Complex lipids found in SB oil are phospholipids, glycolipids, and sterols [8].

Phospholipids and Glycolipids
Phospholipids, as fatty acid esters of glycerol or sphingosine as a base, have one or more fatty acids attached together with a phosphate group and an alcohol linked to it.The fatty acid part of the molecule is hydrophobic, while the rest is hydrophilic [36].These lipids, with a moisturizing and softening skin effect, are known to improve elasticity of the skin, reduce inflammation, and promote skin regeneration and cell renewal [37].Lecithin or phosphatidylcholine is characterized by moisturizing and cell renewal properties, delays the aging process, and may help removing excessive sebum from the hair.According to the literature data, there is a range from 0.2-0.5 to 1 wt % of phospholipids in the SB oil from fruit pericarp (of which about 5.8 wt % is lecithin) [8].

Sterols
Sterols are solid alcohols of the steroid group [16].They strengthen the lipid barrier of the skin, protect the skin from external noxious substances, and decrease the water loss, improving skin elasticity and firmness.The sterols in SB oil may originate from the seed (0.1-0.2%) or from the pericarp (0.02-0.04%) [29].Beta-sitosterol as a main sterol compound makes up 57-83 wt % of total sterols and 576.9 mg/100 g of oil [38].There has been 60-70% of sitosterol in SB oil from the seeds and 80% of sitosterol in SB oil from the fruit pericarp.Isofructosterol is present in concentrations of 10-20% in SB seed oil and of 2-5% in the SB fruit pericarp oil.Campesterol, stigmasterol, citrostadienol, avenasterol, cycloartenol, and obtusifoliol have also been identified in the seed oil [29,39].
This complex lipid composition makes SB oil suitable for cosmetics and cosmeceuticals [37].

Internal Application of Sea Buckthorn Benefits for Human Health
Sea buckthorn fruits have been used in ancient Indian, Chinese, and Tibetan medicine for dysfunctions of alimentary, respiratory, and circulatory system.SB oil used internally has positive effects on the digestive system lowering inflammation.Oral application is adjuvant in the treatment of gastric, duodenal, and intestinal ulcer [8,40].It has been shown to reduce inflammation processes in the vagina and cervix [41].A high amount of vitamin C makes it suitable for immune deficiencies; due to its antioxidant activity, it removes free radicals and strengthens the immune system [32,42].SB oil lowers blood cholesterol, which helps to prevent atherosclerosis [43,44].At a university in Finland, sea buckthorn was tested and shown to significantly increase the level of beneficial high-density lipoprotein (HDL) cholesterol fraction [17].It reduces the risk of thrombophlebitis and is enrolled in the control of bleeding [45].Febrile states respond positively to SB oil [46], as well as symptoms of rheumatoid disease [6].Some of the lipophilic components (ά-and γ-linolenic acids) of SB oil positively influence brain functions and the central nervous system by an antidepressant effect [47].Its advantage as an adjuvant in cancer therapy is that fastens regeneration after use of chemotherapy.The favoring feature of SB oil is that it is considered safe, with no potential harmful effects.It can be consumed by pregnant and breastfeeding women [8].
The suggested pharmaceutical form that would be ideal for the application of SB oil are capsules, because of the problem with rancidity (presence of unsaturated fatty acids) [5].Different fractions of SB fruits were investigated for antioxidant activity and its relationship to different phytonutrients.The capacity of the crude extracts, such as the phenolic and ascorbate extracts, to scavenge radicals decreased significantly with increased maturation.The antioxidant capacity of the lipophilic extract increased significantly and corresponded to the increase in total carotenoids [48].

External Application of Sea Buckthorn Benefits for Human Health
In comparison to other vegetable oils, SB oil is considered to have a unique composition of carotenoids, fatty acids, and complex lipids [23,31].
SB oil contains a rare palmitoleic acid (ω-7 acid), a component of skin lipids, that stimulates regenerative processes in the epidermis and promotes wound healing.In other words, the oil has the ability to activate physiological skin functions for minimizing scars and skin regeneration.The proposed mechanisms of action of SB oil are the stimulation of epidermis regeneration and collagen synthesis, so SB oil was found to stimulate wound healing, even healing of necrotic tissue [5,49].These mechanisms have been connected to the content of unsaturated ω-3 and ω-6 fatty acids, carotenoids, and tocopherols, which stimulate fibroblast proliferation, collagen biosynthesis, and expression of specific matrix metalloproteinases that induce tissue reparation and angiogenesis [50].Preparations containing SB oil have been found to promote wound healing.In the presence of liquid crystals, SB oil may exhibit wound healing even in a lower concentration [51].
SB oil has been used in the treatment of different skin diseases (e.g., eczema, dermatoses, ulceration, psoriasis, and atopic dermatitis).Externally applied SB oil may also reduce bedsores, spots, acne, scars, discoloration, and allergic and inflammatory lesions of the skin [33,52].

SB Oil in Cosmetics
SB oil used in cosmetics has been obtained by different processes and is intended for the treatment of mature skin [5,12].One of the ways to obtain lipids for cosmetics is to squeeze berries in order to obtain the juice that separates into three layers.The upper layer is a thick orange cream, the middle is a mixture of UFAs and SFAs, and the lower layer is watery juice.The two upper layers have been processed and used for making skin care products [26,29].
Both SFAs and UFAs in SB oil improve the level of skin hydration.Ω fatty acids-oleic acid as ω-9, linoleic acid as ω-6, and ά-linolenic acid as ω-3 acid reduce transdermal water loss [53,54].UFAs are part of the receptors that stimulate the production of skin barrier lipids and proteins-precursors of the natural hydrating factor [33]. Research has shown that the one-time application of creams consisting of natural emollients (such as SB oil or olive oil, both in concentrations of 40%) lead to a statistically significant increase in skin hydration, compared to creams with the same quantity of synthetic emollient (such as isopropyl myristate).None of the formulations change pH values of the skin [50,55].
Components of SB oil reach different layers of epidermis, due to the presence of fatty acids with various properties that enhance dermal transportation [32].SB oil, as a powerful antioxidant, may delay the aging process by removing free radicals.Most commonly, it is added to anti-aging and anti-wrinkle cosmetics due to its firming and tonifying properties for aging skin [5].Hwang et al. (2012) suggested a sea buckthorn fruit blend against skin aging, because it functions by regulating moisture content, matrix metalloproteinase expression levels, and superoxide dismutase (SOD) activity [56].SB oil alleviates dry, irritated, rough, flaking, and itchy skin [57].Skin damage caused by exposure to UV radiation or X-rays is successfully treated with SB oil due to its high concentration of carotenoids and tocopherols [58].It can also be used as an adjuvant therapy for skin alterations caused by chemical compounds [5].
SB oil is often used in different cosmetic procedures (peelings, baths, masks, hair removal, etc.) due to its smoothing effect on the skin [8].It strengthens hair, so it has been used in shampoos, conditioners, and other hair products, targeting the recovery of the damaged hair, elasticity restoration, and the prevention of hair loss.Intensive color of the oil is due to its carotenoid concentration, which makes skin more elastic after cutaneous applications [8,59].

Conclusions
Hippophae rhamnoides is a plant that has been researched in different fields-biotechnology, nutraceutical, pharmaceutical, cosmetic, and environmental sciences.Berries of sea buckthorn contain fatty oil.A complex but well-balanced composition of lipids and other ingredients of SB oil makes it suitable for cosmetics and especially for cosmeceuticals.
As the mechanisms of action by which the external application of SB oil achieves medical benefits have been increasingly specified, this natural substance has become more valuable in cosmeceuticals.Use of SB oil may lead to an increased number of possible formulations, which may in turn lead to improved auxiliary treatments of different skin diseases.

Table 1 .
Composition of fatty acids in sea buckthorn (SB) oil.

Table 2 .
The effect of screw press and aqueous extraction methods on changes of nutritional components in oils (the order of increasing concentration: low < high < highest).
* n/a = not applicable, no oil extracted.

Table 2 .
The effect of screw press and aqueous extraction methods on changes of nutritional components in oils (the order of increasing concentration: low < high < highest).
* n/a = not applicable, no oil extracted.

Table 3 .
Composition and significance of micronutrients and macronutrients in fruits (wt %).