Supporting biodiversity is vital

Solar or wind energy pollutes the environment much less than energy generated in coal power plants. Fair trade is a unique means to produce rare and exclusive plant raw material in remote regions in a sustainable way. However, the green trend needs to be seen in a more global context to avoid a negative impact in other areas. The production of one litre of biodiesel needs 4,000 litres of water. Rainforests, hot spots of biodiversity, are destroyed for sugar cane, soy and palm oil production and the prices of crops and food increase because of the higher demand and speculation. The plant kingdom has over 400,000 species of higher plants, 5% with an ethno medicinal background (G. Cordell et al). The majority of these plants has never been investigated phytochemically and represents a large pool for new active ingredients in medicine and cosmetics. The diversity of the plant species correlates with the structural diversity of natural products. Over 10,000 different alkaloids (M. Hesse), over 4,000 flavonoids, over 1,000 saponins are known to date (K. Hostettmann et al). In at least 30% of all higher plant species, volatile substances have been detected. A specific essential oil can consist of a handful to over 300 individual components (R. Kaiser). The exact identification of plant species performed by specialised taxonomists is a crucial factor in phytochemical research. The identification by the analytical profile of secondary metabolites is not possible – the composition and proportions of natural products in an extract depend on environmental, in addition to genetic, factors. The infection of a plant by fungi is able to trigger the biosynthesis of phytoalexin-like natural products.

Plant extracts and natural products for cosmetic use
Different types of plant-based active ingredients are used in cosmetics. They cover the range from label claim diluted extracts to purified natural products or modified natural products. Label claim extracts: usually come from well-known plants, are diluted and use the marketing image of the plant. No activity can be attributed to the natural products present in strongly diluted concentrations. These extracts are often used in mass market products. Chemically standardised plant extracts: examples are plant extracts standardised on a dominant compound (peak) in the HPLC chromatogram. The specific activity of the extract does not necessarily correlate with this peak. Many plant extracts used in cosmetics are standardised this way. The marketing image of the plant is an important factor. Biologically standardised plant extracts: in a screening a plant extract shows an interesting activity and will be commercialised as an active cosmetic ingredient. The active natural products are identified to standardise the bioactivity of the extract. Natural products and modified natural products: examples of plant-based natural products are listed in Table 1. Bioactive natural products are often reactive and are therefore unstable. A way to increase the stability and improve the skin penetration (bioavailability) of compounds with phenolic groups is to esterify them with suitable fatty acids. The epidermis is known to have a strong esterase activity, hydrolysing those “prodrugs” in the active form during the application of the cosmetic product. The stability of the active cosmetic ingredient is preserved during the shelf life of the corresponding cosmetic product. Once applied on the skin, the active form is released.

 Plant extracts as ‘black boxes’
Plant extracts are “black boxes” containing hundreds of different compounds. The diversity of compounds depends on genetic and environmental factors such as age of the plant, harvest season, soil, nutrients, humidity, altitude and infections. Natural products often tested as raw or partially purified plant extracts in screenings can show activity on numerous targets in genetic, enzyme or cell-based in vitro assays. If the plant extract shows an interesting activity, the challenge is to identify the active compounds. The identification of the bioactive natural products allows the biological standardisation of an active cosmetic ingredient.