A wide range of plant-derived compounds with health-promoting properties and/or their technological characteristics, is available for recovery and use in cosmetic and pharmaceutical formulations.
Plant-derived polysaccharides, vegetable oils and plant-based antioxi-dant phenolic compounds are three of the largest groups of natural compounds that offer such potential because of their relevant beneficial properties. In this chapter, the current literature has been surveyed and the recently recognised health benefits of these specific phytochemicals are reported; their sources, extraction procedures, potential applications and bioactivities are also discussed.
18.3.1 Selected groups of plant polysaccharides: sources and bioactivity
Potentially bioactive polysaccharides have been obtained from a wide range of plant sources. Their carbohydrate composition and structural features are typical of polysaccharides of gums and mucilages, of storage polysaccharides or of cell walls from prokaryotes, fungi, and lower and higher plants (Waldron and Selvendran, 1992).
Plant polysaccharides are a complex and heterogeneous group of compounds. They might have either storage (starch, inuline, glucomannans) or structural (cell wall polysaccharides) functions within the plant. Nevertheless, their chemical composition and structure play an important role in determining the functional properties and potential bioactivity of the polymers (Diallo et al., 2003; Femenia et al., 2003). Thus, plant polysaccharides can be classified in different groups according to their chemical composition and the structural arrangement of the component monosaccharides (Brett and Waldron, 1996).
Glucomannans (or mannans), pectic polysaccharides and glucans are three of the most important groups of plant-derived polysaccharides that have been associated with different bioactivities. Their functional properties, such as the ability to bind water and oil, may also contribute to their potential application in the cosmetics field.
Glucomannans are carbohydrate polymers widely distributed in both hardwood and softwood plants, where they have either storage or structural functions. The polymeric sequence is linear and it is composed of (1^4)-P-d-Glcp and (1^4)-P-d-Manp sugar residues. A considerable amount of work has been carried out based on the bioactivity of glucomannans from two interesting plant sources: Aloe vera and Amorphhophallus konjac.
'Acemannan' from Aloe vera
There are over 300 species of Aloe known, but Aloe vera L. (Aloe bar-badensis Miller) is recognised as the 'true Aloe vera' for its widespread use and purported healing power. The plant belongs to the Liliacea family and it is not member of the cactus family as many would believe from the rosette-like arrangement of the long spiked leaves on the central stem.
Scientific investigations on Aloe vera have gained more attention over recent years due to its reputed medicinal properties. Some publications have appeared in respected scientific journals that have made appreciable contributions to the discovery of the functions and properties of aloe, 'nature's gift'. The use of and research on this plant up to 1998 have been well described in two well-referenced reviews (Grindlay and Reynolds, 1986; Reynolds and Dweck, 1999). Currently, the plant is most widely used in areas of skin care, cosmetics and wound-healing.
Although many physiological properties of Aloe vera have been described, it still remains uncertain as to which of the component(s) is responsible for these properties. The plant contains two separate juice materials, a yellow latex (exudate) and a transparent mucilaginous gel, extruded from the inner pulp. This clear pulp is widely used in various medical, cosmetic and nutraceutical applications (Eshun and He, 2004). Many biological activities (including anti-viral, anti-bacterial, laxative and anti-inflammatory properties, immunostimulation and protection against radiation) have been attributed to this gel, and in particular, its polysac-charides (Ni et al., 2004). The action of aloe gel as a moisturising agent is still a popular concept (Leung, 1998).
Many studies have reported the presence of polysaccharides, especially the acetylated mannan or glucomannan (acemannan, commercially known as CarrysinTM), as the main component of the gel with minor amounts of various other types of polymers (t'Hart et al., 1989; McAnalley, 1993; Femenia et al., 1999; Lee et al, 2001; Ni et al., 2004; Chow et al, 2005).
Acemannan is a storage polysaccharide located within the protoplast of the parenchymatous cells of the Aloe vera parenchyma (Femenia et al., 1999). There is a considerable discrepancy in the literature as to the structure of the acemannan. A recent investigation suggests that the polysac-charide has a P-glucomannan backbone with a Man : Glc ratio of ~15 : 1 and the branching occurs from the O-2, O-3, and O-6 of (1^4)-P-Manp residues to single a-Galp side chains (Chow et al., 2005).
The potential use of Aloe vera products often involves some type of processing. Thus, the main physico-chemical modifications promoted by heat treatment and dehydration at different temperatures on acemannan and cell wall polysaccharides from Aloe vera gel have been recently reported (Femenia et al., 2003; Chang et al., 2006). Appropriate processing techniques should be employed during the stabilisation of the gel in order to affect and extend its field of utilisation.
It seems clear that further research needs to be done to unravel the myths surrounding the biological activities and the functional properties of Aloe vera. Recent studies claim that the relationship between the components, including acemannan, and its overall effect has not been clarified (Choi and Chung, 2003; Eshun and He, 2004), and that some of the bio-activities - such as the prevention or minimisation of radiation-induced skin reactions in cancer patients (Richardson et al., 2005) or, even, the effectiveness of Aloe vera gel for the healing of chronic wounds - could not be demonstrated (Gallagher and Gray, 2003). A more precise understanding of the biological activities is required to develop Aloe vera as a pharmaceutical.
Konjac glucomannan is a food storage polysaccharide extracted in high yield from the tubers of Amorphophallus konjac C. Koch. This plant has been cultivated for centuries in China and Japan and used as food and as a food additive. Only recently has it found use in the West as a texture modifier and thickener. Konjac glucomannan is a P-(1^4)-linked polysaccharide composed of a d-glucosyl and d-mannosyl backbone lightly branched, possibly through P-(1^6) glucosyl units (Katsuraya et al., 2003). The Man : Glc ratio is typically reported to be approximately 1.6 : 1 (Cescutti et al., 2002), being the weight average molecular mass of this polysaccharide 9.0 ± 1.0 x 105 g mol-1 (Ratcliffe et al., 2005). The presence of about 5-10% acetyl-substituted residues confers water solubility on the glucomannan (Gao and Nishinari, 2004).
The studies on the application of konjac glucomannan have been extended greatly from food and food additives to various fields - such as the pharmaceutical, biotechnological and fine chemical industries, including cosmetics (Zhang et al., 2005). In the pharmaceutical area, due to its degradability and gel-forming ability, konjac glucomannan can be used in drug delivery (Wang and He, 2002; Pathak et al., 2003), and it can also be used to improve bio-adhesive properties. Thus, Dettmar et al. (2000) invented a kind of pharmaceutical composition containing an alginate, xanthan, carrageenan and glucomannan; this provided both a protecting and a healing effect on the mucosal surface for treatment of disorders of the oesophagus. Konjac glucomannan has also been used in cellular therapy (Slepian and Massia, 2001) and as a gel filler material for prosthetic implants (Ita and Clarke, 2003).
Regarding cosmetics, different products containing glucomannan have been patented in Japan: Omura et al. (2001) invented a hair composition containing glucomannan; Takada (2000) a kind of water-insoluble glucomannan gel as a mild scrubbing agent; Saito (2000) a product containing pigments coated with water-soluble glucomannan that exhibited good skin-moisturising effects; and Shimizu and Ohshiba (2000) a quick-drying disinfecting gel.
In recent years, pectic substances have emerged as a relevant class of potentially bioactive natural products (Diallo et al., 2003; Hokputsa et al., 2004a, b; Inngjerdingen et al., 2005; Mellinger et al., 2005; Nergard et al., 2005).
Native pectins are believed to consist of a backbone in which 'smooth' galacturonan regions of a-(1^4)-linked d-galacturonosyl residues are interrupted by ramified ('hairy') rhamnogalacturonan regions consisting of a backbone of alternating a-(1^2)-linked l-rhamnosyl and a-(1^4)-linked galacturonosyl residues (rhamnogalacturonan I (RG I)). Neutral side chains are predominantly attached to O-4 of the rhamnosyl residues, and are composed of d-galactosyl and l-arabinosyl residues. The proportion of 'smooth' and 'hairy' regions can vary greatly depending on the type of tissue or its development stage. A minor component of plant cell wall is RG II, which has an extremely complex structure (Voragen et al., 2000).
Pectic substances can be found in relatively large amounts in the cell walls of fruit and vegetable tissues. However, most of the bioactivities associated with pectic polymers have mainly been reported for polysac-charides obtained from herbal and medicinal plants. The pharmacological activity of each of the pectic polysaccharides may depend on their fine chemical structure (Yamada, 1994).
Several polysaccharides isolated from plants used in phytotherapy and traditional medicine have been tested for complement modulating properties. In particular, pectins, arabinogalactans type I ((1^4)-linked Gal) and type II ((1^3,6)-linked Gal), arabinans and other heteroglycans like glu-curonoarabinoxylan have the capacity to stimulate the complement system (Yamada and Kiyohara, 1999; Hokputsa et al., 2004a). The complement system is an important component of the immune defence against infections, and proteolytic cleavage of the complement components leads to generation of biologically active complement activation products that may increase local vascular permeability, attract leucocytes (chemotaxis), mediate immune adherence and modulate antibody production. Agents that improve or stimulate leukocyte locomotion are of interest, as the capacity of leukocytes to respond by chemotaxis is part of an optimal host defence against infection. Very often, chronic and recurrent infections, cancer and rheumatoid arthritis are associated with diminished chemotaxis in vitro (Wagner and Jurcic, 1991).
Two acidic polysaccharides that exhibited intestinal immune system modulating activity were characterised by Yu et al. (2001) from rhizomes of Antractylodes lancea DC. The chemical composition of these two polysaccharides closely resembled RG I and RG II, although small differences that could affect their bioactivity were reported.
The aqueous extract of the dried leaves of Trichilia emetica contained different types of pectins with a rhamnogalacturonan backbone that might be responsible for the complement fixing activities observed (Diallo et al., 2003). Interestingly, the removal of terminal arabinofuranosides promoted a dramatic decrease of the activity, indicating that this structural unit may be involved in the bioactive site of the molecule.
The immunomodulating activities of different fractions isolated from 50 and 100 °C water extracts from the roots of Vernonia kotschyana - a traditional herbal plant used for the treatment of gastritis and gastro-duodenal ulcers, and as a wound-healing remedy - were investigated by Nergard et al. (2004). The active principles were identified as acidic polysaccharide fractions containing pectic arabinogalactan II structures, which showed both complement fixing ability and T-cell-independent induction of B-cell proliferation in vitro. Some activity was also observed on macrophages.
The same research group has investigated the anti-ulcer, radical-scavenging and immunological activities of pectin-type polymers from the aqueous extract of the roots of Cochlospermum tinctorium, a plant of widespread occurrence in the savannah and scrub land of the drier parts of the West African Region (Nergard et al., 2005). The polysaccharides extracted were shown to be of a very complex nature possibly with a highly branched RG I core with both arabinogalactan type I and type II side chains. The polysaccharides possessed both mitogenic and complement fixation activities, and may therefore, at least partly be responsible for the immuno-modulating activities observed for the crude extract.
Furthermore, two pectin-type polysaccharides isolated from a 50 °C water extract from the aerial parts of Glinus oppositifolius were shown to exhibit dose-dependent complement fixating activities, and induced chemo-taxis of macrophages, T-cells and natural killer (NK) cells (Inngjerdingen et al., 2005).
Finally, Trommer and Neubert (2005) reported the protective effects of the lipids within the human skin; they used a topical application of a semisolid formulation rich in pectic polysaccharides. The administration of lipid protective polysaccharides in cosmetic products could be helpful against ultraviolet (UV)-induced damage.
Extensive studies have demonstrated that (1^3)-P-d-glucans, and (1^3)-linked linear and branched glucose homopolymers exhibit considerable immunomodulatory activity by binding specific macrophage receptors and activating macrophages, resulting in anti-tumour, anti-bacterial and wound-
healing activities (Ooi and Liu, 2000; da Silva and Parente, 2003; Peng et al., 2003; Wu et al., 2005). Moreover, (1^3)-P-d-glucans show other biological activities potentially exploitable in therapy as clinical immuno-stimulants (Liang et al., 1998).
Many of the bioactive (1^3)-P-d-glucans are fungi-derived polysacchar-ides. Thus, Madla et al. (2005) have recently described polymer production and some biological properties (anti-viral and anti-fungal activities and cytotoxicity) of the polymers from 16 strains of fungi from 15 different genera. Three strains contained polymers that induced the production of cytokine, which is known to stimulate the wound-healing process. These polysaccharides have been characterised by Methacanon et al. (2005) and they were shown to be composed of a (1^3)-P-d-glucan backbone substituted at O-6 with side chains of (1^6)-P-d-glucopyranosyl units. Polymers with similar structure have been obtained from Ganoderma tsugae, a mushroom used in traditional Chinese medicine. Recently these fungi have attracted much attention because their polysaccharides have been demonstrated to exhibit remarkable anti-tumour activities. These were manifested by enhancing the host-mediated mechanisms including increasing inter-leukin-2 (IL-2) production and stimulation of cytotoxic T-lymphocytes, NK activity and antibody production (Peng et al., 2003, 2005a, b).
The poor aqueous solubility of some of the glucans obtained might be a huge hindrance to their application, especially in pharmaceuticals. Biotechnological processes such as sulphation have been proposed to improve polysaccharide polarity and aqueous solubility (Wang et al., 2005). Interestingly, a water insoluble (1^3)-a-d-glucan isolated from the fruiting body of Ganoderma lucidum did not exhibit any anti-tumour activity whereas its sulphated derivative showed anti-tumour activity (Zhang et al., 2000).
Sulphated polysaccharides are one of the few natural compounds with excellent and promising anti-viral activities that have proven effective in reducing human immunodeficiency virus (HIV) replication and progress (Asres et al., 2005). It is very much hoped that anti-HIV cures and prophylactic preparations containing these natural compounds may eventually be produced.
Bioactive components in mushrooms have also been the focus of recent research on anti-tumour, anti-viral and anti-bacterial actions. Glucans and glucan-protein complexes are amongst the potential compounds that might be responsible for such bioactivities (Dikeman et al., 2005; Hoshi et al., 2005; Ou et al., 2005; Wong and Cheung, 2005).
Chitin is the second most abundant bioplolymer on Earth after cellulose; it is available largely in the exoskeletons of invertebrates, but also in the cell walls of fungi (Kumar, 2000). Chitosan is the name used for low-acetylated substituted forms of chitin. They belong to the family of the linear copolymers of P-(1^4)-2-amino-2-deoxy-d-glucan (GlcN or glucosamine units) and P-(1^4)-2-acetamido-2-deoxy-d-glucan (GlcNAc or acetylglucosamine units) (Qin et al., 2004). Valuable applications for chitin and chitosan have been reported in many fields such as chemistry, biotechnology, pharmaceutics and cosmetics (Kumar, 2000; Synowiecki and Al-Khateeb, 2003; Yusof et al., 2003; Kumar et al., 2004; Muzzarelli et al., 2005).
18.3.2 Plant-derived antioxidants: phenolic compounds Plant-based diets are widely suggested to contribute to reducing the risk of development of chronic diseases such as cancer, atherosclerosis, cardiac dysfunction, diabetes, hypertension and neurodegenerative disorders. Most of these functions have largely been attributed to the antioxidant effects of their bioactive components. The growing interest in the substitution of synthetic food antioxidants by natural ones has fostered research on vegetable sources and the screening of raw materials to identify new antioxi-dants. Oxidation reactions are not an exclusive concern of the food industry, and antioxidants are widely needed to prevent deterioration of other oxidis-able goods, such as cosmetics and pharmaceuticals.
Interestingly, within the antioxidant literature, the number of residual sources studied has been augmented considerably, due mainly to the value-adding/recycling interest of the agro-food industry, and a requirement for information on the specific location of active compounds and their modification during processing (Peschel et al., 2006).
Several plants have been proposed as sources of potentially safe natural antioxidants for the food, pharmacological and cosmetics industries; various compounds have been isolated, many of them being phenolic compounds. A large number of low and high molecular weight plant polyphenolics presenting antioxidant properties were studied and proposed for use in preventing lipid oxidation (Hagerman et al., 1998).
Sources and potential applications of phenolic compounds Phenolic compounds are secondary metabolites that are derivatives of the pentose phosphate, shikimate and phenylpropanoid pathways in plants (Randhir et al., 2004). Their chemical structure is characterised by the presence of an aromatic ring, bearing one or more hydroxyl substituents and ranges from simple phenolic molecules to highly polymerised compounds (Bravo, 1998). Despite this structural diversity, the group of compounds are often referred to as 'polyphenols' (Balasundram et al., 2006).
The phenolic metabolites include: anthocyanins, anthochlors, benzofurans, chromones, coumarins, minor flavonoids, flavonones and flavonols, isoflavonoids, lignans, phenols and phenolic acids, phenolic ketones, phe-nylpropanoids, quinonoids, stilbenoids, tannins and xanthones (Bahorun et al., 2004). Flavonoids constitute the largest group of plant phenolics, accounting for over half of the 8000 naturally occurring phenolic compounds (Heim et al., 2002).
The antioxidant activity of phenolic compounds is due to their ability to scavenge free radicals, donate hydrogen atoms or electrons, and chelate metal cations (Amarowicz et al., 2004).
The possible health benefits derived from dietary phenolic compounds depend on their absorption and metabolism, which in turn are derived from their structure including their conjugation with other phenolics, degree of glycosylation/acylation, molecular size and solubility (Bravo, 1998).
A wide range of physiological properties such as anti-allergenic, anti-atherogenic, anti-inflammatory, anti-microbial, antioxidant, anti-thrombotic, cardioprotective and vasodilatory effects have been reported for phenolic compounds (Benavente-Garcia et al., 1997; Samman et al., 1998; Middleton et al, 2000; Puupponen-Pimia et al., 2001; Manach et al, 2005).
As in food products two applications of phenolic antioxidants might be of interest: as a substitute for synthetic preservatives or as active ingredients, for example as a skin-protecting additive in dermatology. Investigations on the commercial application of radical scavengers and flavonoids, the main group of phenolic compounds, as beneficial anti-ageing and photoprotection ingredients in cosmetic products have been reported by Katiyar and Elmets (2001) and Lupo (2001). Furthermore, an increase in the demand for non-toxic antioxidants that are active in hydrophilic and lipophilic systems has been observed (Peschel et al., 2006).
Phenolic compounds are present in almost all foods of plant origin. Fruit, vegetables and beverages such as fruit juices, tea and wines are the major sources of these compounds. Plant by-products and medicinal plants are also important sources of phenolic compounds.
Phenolic compounds have been closely associated with the health benefits derived from consuming high levels of fresh fruits and vegetables (Parr and Bolwell, 2000). There are wide variations between the total phenolics contents of the different fruits or vegetables, or even for the same fruits and vegetables, reported by different authors (see review of Balasundram et al., 2006). These differences have been attributed either to the complexity of these groups of compounds or the methods of extraction and analysis utilised (Bravo, 1998). Moreover, the total phenolics contents of plants depend on a number of intrinsic (genus, species, cultivars) and extrinsic (agronomic, environmental, handling and storage) factors (Tomas-Barberan and Espin, 2001).
Fruit and vegetables containing high levels of phenolic antioxidants would be attractive to health-conscious consumers, therefore optimisation of production and processing factors affecting the antioxidant capacity is desirable. Food-processing practices such as heat and aeration may decrease the antioxidant capacity of fruit phenolics (Kalt et al., 2001).
Flavonoids are present in many fruits and vegetables such as grapes, apples and onions. Their cardioprotective effects stem from the ability to inhibit lipid peroxidation, chelate redox-active metals and attenuate other processes involving reactive oxygen species (Heim et al., 2002).
Administration of polyphenol-rich fruit juices is thought to be favourable to HIV-positive patients due to enhanced phytohaemagglutinin-induced lymphocyte proliferation, which could restore T-cell homeostasis (Winkler et al., 2004). Wines as natural sources of antioxidants with radical-scavenging properties are the subject of growing interest (López-Vélez et al., 2003; Lugasi and Hovari, 2003; Stasko et al., 2006). The major phenolic constituents of wines include hydroxybenzoic and hydroxycinnamic acids derivatives, as well as flavonols (Minussi et al., 2003). The phenolics contents and composition in wines vary widely and are determined by several factors, such as the variety of grapes used, the conditions under which they were grown, wine-making techniques, maturity and processing parameters (Villaño et al., 2006). Moderate wine consumption has been related to prevention of cancer, Alzheimer's disease and dementia, and it has also been implicated in decreasing the risk of coronary heart disease (Renaud et al., 1998).
The findings of many studies using green tea polyphenols as chromopre-ventive, natural healing and anti-ageing agents for human skin, and discussion of possible mechanisms of action, have recently been summarised by Hsu (2005).
Processing of plant foods might result in the production of by-products that are potentially rich sources of bioactive compounds, including phenolic compounds (Schieber et al., 2001). The availability of phenolic compounds in industrial residues, their extraction and antioxidant activity has been the subject of a review by Moure et al. (2001).
The by-products of the grape/wine industry have recently attracted considerable interest as a source of phenolic compounds (Louli et al., 2004; Selga et al., 2004; Kammerer et al., 2005a, b). Grape skins and seeds contain flavonoids (catechin, epicatechin, procyanidins and anthocyanins), phenolic acids (gallic and ellegallic acids) and stilbenes (resveratrol and piceid). These grape seed and skin constituents have been shown to have health-functional properties comparable with those of fruits and vegetables (Yilmaz and Toledo, 2006).
In addition, citrus industry by-products, if utilised optimally, could also be major sources of phenolic compounds as the peels, in particular, have been found to contain higher amounts of total phenolics compared with the edible portions (Gorinstein et al., 2001; Mandalari et al., 2006). The peels of several other fruits have also been found to contain higher amounts of phenolics than the edible fleshy parts. For instance, peels from apples, pears, pomegranates, mango and peaches were found to contain larger amounts of total phenolics than those found in the peeled fruits (Gorinstein et al., 2002; Berardini et al., 2005). The peels of pomegranate - which contained larger amounts of total phenolics, flavonoids and proathocyanidins than a pulp extract - have demonstrated their effectiveness in the prevention of atherosclerosis (Li et al., 2006).
Lu and Foo (1997) identified and quantified the major polyphenols in apple pomace. Thus, epicatechin, caffeic acid, three dihydrochalcone gly-cosides and five quercitin glycosides were isolated. The same authors also studied the procyanidins obtained from apple pomace. The homogeneous nature of the procyanidin fractions was demonstrated by the isolation and identification of a range of epicatechin oligomers (Foo and Lu, 1999). The antioxidant and radical-scavenging activities of all the phenolic compounds identified and isolated from apple pomace was tested. All the compounds exhibited strong antioxidant activities; their 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH)-scavenging activities were 2-3 times better, and the superoxide anion radical-scavenging activities 10-30 times better, than those of antioxidants such as vitamins C and E (Lu and Foo, 2000).
The by-products of the olive industry have also received much attention as a source of phenolic compounds, in particular hydroxytyrosol, tyrosol, oleuropein, and a variety of hydroxycinnamic acids that can be recovered from the olive mill wastes (Obied et al., 2005). These compounds are shown to be essentially hydrophilic, and this is the reason why they are more abundant in olive oil waste waters. Oleuropein and hydroxytyrosol exert protective effect against auto-oxidation of LDL in vitro (Visioli et al., 1995), and their free-radical-scavenging activity has also been demonstrated (Visioli and Galli, 2002). Hydroxytyrosol appeared to be the most effective phenolic compound at low concentrations to protect human erythrocytes and DNA against oxidative damage (Quiles et al., 2002). A new enzymatic treatment of olive oil by-product using fungal enzymes to release simple phenolic compounds, especially hydroxytyrosol, has been reported by Bouzid et al. (2005). The antioxidant capacity of hydroxytyrosol was higher than that of antioxidants such as ascorbic acid and butylated hydroxytolu-ene (BHT).
The screening of up to 70 medicinal plant extracts for antioxidant capacity and total phenolics content has recently been reported by Katalinic et al. (2006). The results indicate that Melissae folium infusions could be an important source of phenolics with high antioxidant capacity comparable with red wine or beverages like tea. The possible role that flavonoids from rosemary (Rosemary officinalis) and other medicinal herbs play in the prevention of neurodegenerative diseases has been reviewed by Arouma et al. (2003).
So far the extraction of antioxidants, including phenolic compounds, from plant tissues has been accomplished by employing as extraction solvent, a liquid, such as methanol, ethanol, acetone, ethyl acetate, an aqueous solution of the aforementioned solvents, or even a supercritical fluid (Louli et al., 2004). In any case, the composition of the extract depends not only on the solvent used, but also on the quality and the origin of the plant material, its composition, its storage conditions and its pretreatments. All these parameters should be taken into account, in order to produce a high-quality extract with antioxidant activity suitable for use in the food, cosmetic and pharmaceutical industries.
For solid-liquid extraction, an appropriate organic solvent is mixed with the plant material extracting the phenolic compounds. Then, the removal of the solvent can be achieved by means of different processes such as drying, concentration or ultrafiltration (UF). After applying any of these procedures, the extract must be dried to obtain a powderform.
Organic solvent extraction is efficient and simple, yet costly. Large amounts of organic solvents are often used. This, in turn, is also detrimental to human use because traces of the organic solvent may be present in the antioxidant extract. Phenolics separation and concentration by membrane separation is even more efficient than organic solvent extraction. Organic solvents are still used but in lower quantities, and UF ensures the purity of the polyphenol extract. The drawback is membrane fouling, which can disrupt the process, and the time needed to complete the process. The separation process has to be repeated several times.
Alternatively, SCFE can also be used, which produces the final product as a powder without any need for final drying. Furthermore, the advantages of using CO2 - low cost, non-toxic, non-flammable, and non-corrosive -make it the perfect solvent for natural products. It is imperative to have safe and efficient extraction procedures that guarantee a pure product. According to Shi et al. (2005) SCFE is the extraction process of the future. However, it has been reported that the recovery of antioxidants with supercritical CO2 often might require intense extraction conditions such as a pressure higher than 300 bar, and, in the case of phenolic compounds from grapes, a modifier in a high percentage was also required (Murga et al., 2000).
In contrast to the above, SCFE has also been employed for the purification of the primary extract (Ribeiro et al., 2001), in order to improve its properties without causing any thermal or chemical degradation. In this way, a high-added-value product could be obtained with only moderate conditions and equipment capacity needed, justifying the choice of a supercritical fluid both from an economic and process efficiency point of view.
Cosmetics and pharmaceuticals 485 18.3.3 Oils derived from plant sources
Plant oils are typically composed of triglyceride molecules (esters) composed of a 3-carbon alcohol (glycerol) plus three 18-carbon (or 16-carbon) fatty acids. Unlike the saturated fatty acids of animal fats, which are solid at room temperature, most plant-derived fatty acids are typically unsatu-rated, are liquid at room temperature and are often referred to as oils. Unsaturated fatty acids might contain one or more double bonds between the carbon atoms (mono-unsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs)).
Many non-food applications have been proposed for plant oils. Undoubtedly, cosmetics is one of the fields where these compounds have attracted major attention. However, some of these plant-derived oils have also found interesting applications in the pharmaceutical area (Barrault et al., 2002).
When polyunsaturated vegetable oils are partially hydrogenated to improve their texture, trans fatty acids are produced. Trans fatty acids tend to raise the level of LDLs and lower the level of HDLs. These changes in blood lipids (cholesterol levels) may increase the risk of heart disease (atherosclerosis). Dieticians generally recommend the use of mono-unsaturated, unhydrogenated oils such as olive oil whenever possible, and the avoidance of trans fatty acids found in many products such as french fries, doughnuts, chips, cookies and crackers.
Most fresh fruits exhibit a very low content of fat; in contrast, dry fruits and many fruit seeds and fruit kernels contain large amounts of, often discarded, high-value oils. Selected sources of vegetable oils that are potentially useful for incorporation in cosmetics and pharmaceutical products are reviewed below.
Olive (Olea europaea) oil is currently one of the most appreciated vegetable oils and a key component of the so-called 'Mediterranean diet'. The nutritional and health aspects of olive oil have been reviewed by Harwood and Yaqoob (2002). Olive oil contains oleic acid (55-83% depending on the olive variety) and also a-linoleic acid (5-15%) as the main fatty acids. Diets high in a-linoleic acid delay and prevent diseases such as coronary heart disease, contributing to a high life expectancy (Vardavas et al., 2006). Apart from fatty acids and triglycerides, olive oil contains tocopherols, squalene, carotenoids, sterols, polyphenols, chlorophylls, and volatile and different flavour compounds. The extracts of mixtures of olive fruits, leaves and stems show anti-inflammatory and active oxygen-scavenging effects. The anti-inflammatory effect is exerted by both unsaponifiable and polar compounds (De la Puerta et al., 2000), while the free-radical-scavenging effect of virgin olive oil is mainly due to the presence of polyphenols (Perricone,
2001). Olive oil has been used to moisturise dry skin, and as a lip balm, shampoo, hand lotion, soap, massage oil and dandruff treatment (Bruneton, 1999). It is applied topically to treat skin damage, such as dermatitis, eczema, seborrhoea, psoriasis, thermal and radiation burns, other types of skin inflammation and ageing (Perricone, 2001). When the oil is topically applied after UVB exposure it can effectively reduce UVB-induced skin tumours, possibly via its antioxidant effects (Budiyanto et al., 2000). Adverse cutaneous reactions to topically applied olive oil are seldom reported, but olive oil is considered in general as very weakly irritant (Kranke et al., 1997). There is good evidence that olive oil is protective in cardiovascular diseases, its mechanisms may involve blood lipids, but other mechanisms -including effects on immune function, endothelial function and the coagulation pathways - remain possible and are being actively researched.
Large amounts of seeds from different fruits such as apricots, peaches or cherries are discarded annually at processing plants. This not only wastes a potentially valuable resource but also aggravates an already serious disposal problem. At present there is no systematic collection and utilisation of most of these fruit seeds; thus, valuable products with a large industrial potential remain unexploited. Some of the seeds are difficult to collect because of the direct consumption of the fresh products by consumers, but the bulk of the fruit and vegetable sources are used in food-processing plants.
The oil content of apricot kernel ranges from 40 to 56% of the dry kernel. In general, sweet kernel varieties contain larger percentages of oil than bitter kernelled varieties (Femenia et al., 1995). Nevertheless, oils from both kernel varieties exhibit a fairly similar fatty acid composition, being very rich in unsaturated fatty acids; thus, oleic (~64%) and linoleic (3031%) represent about 93-94% of total fatty acids in both oils (Femenia et al., 1995; Gandhi et al, 1997; Ozkal et al, 2005a). The total oil content and fatty acid composition of apricot kernel oil can be compared with that of almond oil (Carratala et al., 1998; Sánchez-Bel et al., 2005) and cherry kernel oil (Chandra and Nair, 1993). Nevertheless, although it belongs to the same family, peach kernel oil has a slightly different fatty acid profile, containing up to 21% of saturated fatty acids, mainly palmitic acid (Rahma and Abd El-Aal, 1988).
Almond oil is highly appreciated, especially in cosmetics. A typical use of this oil is the application to the skin of neonates during their early stages of life. Furthermore, a role for almond oil in the prevention of colon cancer has also been reported (Davis and Iwahashi, 2001).
One of the big constraints to the use of fruit kernels from bitter varieties of the Rosaceae, not only from a nutritional point of view but also for their utilisation in non-food areas such as cosmetics and/or pharmacology, is the presence of significant amounts (up to 5-6% of the dry kernel of almonds, apricots and peaches) of the toxic cyanogenic glycoside amygdalin (Femenia et al., 1995; Gómez et al., 1998; Dicenta et al., 2002). The removal of amygdalin by biotechnological means, i.e. by using the endogenous enzymes combined with microbial fermentation (Tungel et al., 1998) or by extraction with different solvents (Koo et al., 2005), is required in order to obtain a completely safe product.
Unlike vegetable oils and animal fats, jojoba (Simmondsia chinensis) oil is not a triglyceride but a mixture of long chain esters (97-98%) of fatty acids and fatty alcohols, and therefore is more properly referred to as a wax; however, jojoba oil-wax is the term in general use (Canoira et al., 2006). Jojoba seeds contain about 50% of liquid wax which is mainly used in cosmetic preparations (Cappillino et al., 2003), not only acting as a humectant, but creating a protective film over the skin that keeps in moisture (Dweck, 1997b). Jojoba oil-wax provides a broad spectrum of fatty acids (such as oleic, linoleic and arachidonic), as well as triglycerides which have good compatibility with the natural sebum in the human skin (van Boven et al., 2000). Pharmaceutical applications of jojoba oil-wax have also been suggested (Ash et al., 2005). Screening of the oil revealed that it has significant analgesic, antipyretic, anti-inflammatory, antioxidant, anti-bacterial and anti-parasitic properties (Bruneton, 1999).
Apart from its popular edible fruit, mangoes (Mangifera indica) also contain kernels that yield a valuable emollient oil rich in oleic and stearic acids, and triglycerides, and is used in cosmetics (Aikawa, 2002). Mango kernel oil has been investigated for its suitability as an ointment base, and has been observed to release drugs at a remarkably greater rate than the standard paraffin-base ointment formulations (Dweck, 1997a).
Coconut Cocos nucifera (Arecaceae) oil is valued as an emollient and is used as an ingredient in remedies for skin infections. Modified coconut oil containing polyunsaturated fatty acids in the form of mono-, di- and triglycerides is useful as a constituent of a barrier lipid mixture in cosmetic and pharmaceutical formulations to protect and prevent drying of the skin. However, because of its alkali laurate content some coconut oil soaps can irritate the skin (Dweck, 1997a).
Sunflower seeds from Helianthus annuus (Compositae), contain polyun-saturated fats, rich in triglycerides of linoleic acid, an essential fatty acid needed by the body to maintain good skin condition. Studies indicate that cutaneous application of the sunflower oil increases the linoleic acid levels of the skin, lowers transepidermal water loss and helps to eliminate scaly lesions common in patients with essential fatty acid deficiency. Sunflower oil is used for psoriasis, and on bruises (Dweck, 1997b).
Castor oil is obtained from the castor bean, Ricinus communis (Euphorbiaceae). The seeds contain 50% of the oil. The oil acts as a barrier agent to protect against harsh climates, and is soothing to the skin. Castor oil forms a clean, light-coloured, transparent soap, which dries and hardens well and is free from odour (Matsumura, 2001). Ricinoleic acid and its many derivatives have skin smoothing and moisturising qualities, and improve various skin conditions such as rough skin and acne (Miyahara and Sanbe, 2002). Hydrogenated castor oil and/or its esters, are useful as vehicles or carriers, emollients or solubilisers for toiletry, cosmetic, hair and skin care formulations, and are useful for cleansing and conditioning the skin (Sato, 2002).
Cocoa butter, from Theobroma cacao (Sterculiceae), contains triglycerides consisting mainly of oleic, stearic and palmitic acids, and about 75% of fatty acids are present as mono-unsaturates. Cocoa butter is particularly soothing after windburn or sunburn. It is used medicinally as a vehicle in suppositories and pessaries. Cocoa butter is used widely as an emollient and in various topical cosmetic preparations (Dweck, 1997a).
Other potentially interesting plant oil sources that are either currently used or have the potential to be used in the cosmetics and/or pharamaceuti-cal areas, supported by scientific reports about their health-promoting properties, are: goldenberry oil (Ramadan and Morsel, 2003), kukui nut oil (Ako et al., 2005), argan oil (Rojas et al., 2005), date seed oil (Besbes et al., 2004), Amaranthus oil (He and Corke, 2003; He et al., 2003) and Echinacea seed oil (Oomah et al., 2006).
As in the case of plant antioxidants, an attractive alternative to conventional extraction of oils using organic solvents is the application of supercritical fluids. SCFE has been widely used since it enables the recovery of valuable oils from natural matrices; high yields and better quality products with improved functional and/or nutritional characteristics are produced by operating under a wide range of conditions (Ozkal et al., 2005b). In addition, easy and complete removal of the solvent from the final product makes it advantageous over conventional solvent extraction. CO2 is also the most preferred supercritical solvent in oil extraction because of its low critical temperature (31 °C), non-toxic, non-explosive nature, and low price. Supercritical CO2 (SC-CO2) was successfully used for the extraction of oils from different plant sources including rapeseed (Eggers, 1985), peanut (Goodrum and Kilgo, 1987), canola (Temelli, 1992), almond (Marrone et al., 1998; Femenia et al., 2001), pistachio nut (Palazoglu and Balaban, 1998), sesame (Odabasi and Balaban, 2002), walnut (Oliveira et al., 2002), Amaranthus grain (He et al., 2003), carrot root (Ranalli et al., 2004) and apricot kernel (Ozkal et al., 2005a, b).
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