Over the last few years, the amount of scientific literature about the bioac-tivity and health-promoting properties of plant-derived compounds such as polysaccharides, phenolic compounds and vegetable oils has increased. This fact demonstrates the growing interest in the exploitation of plant-based by-products and/or co-products, for instance as potential sources of pharmaceutical and cosmetic products. However, this promising field requires interdisciplinary research of many areas such as food/plant technology, food chemistry and biochemistry, nutrition and toxicology amongst others.
Some industrial activity has already been established based on the health-promoting properties, although not always scientifically supported, of several plants and plant-derived compounds, especially in the cosmetics area (for example: Aloe vera derivatives, different vegetable oils and a wide variety of 'medicinal plants'). However, as it can be inferred from the vast, recent and even sometimes contradictory, scientific literature, most of the potential of many plants and specific plant-derived compounds remains almost completely unexplored.
Although the future of plant-derived co-products holds exciting opportunities for the food, pharmaceutical and cosmetics industries to create novel and high-value products, in order to achieve and optimise their exploitation the following research needs will have to be addressed. (1) Methods for complete utilisation of plant by-products (resulting mainly from food processing), on a large scale and at affordable levels, should be developed. Thus, active participation of the food and allied industries with respect to sustainable production and waste management is required. (2) The bioactivity, bioavailability and toxicology of plant-derived compounds need to be carefully assessed by in vitro and in vivo studies. The 'bioactivity' of many phytochemicals has only been tested in in vitro models and this may bear no relationship to the situation in vivo (Dillard and German, 2000). In addition, there is an urgent need to standardise the methodology applied to determine the bioactivities of different compounds, e.g. of plant polysaccharides, or the antioxidant capacity of compounds such as plant phenolics (Huang et al., 2005). (3) The stabilisation of many plant antioxidants, e.g. phenolics, is a clear area that requires further research. For instance, although the majority of the evidence shows remarkable benefits of the antioxidant, anti-cancer, anti-ageing and anti-inflammation effects of plant phenolics, standard delivery systems for topical application have not been fully established. This is partially because of the nature of these highly reactive compounds, which are easily oxidised in the environment and gradually lose their activity if not used immediately after preparation. Therefore, the primary goal for a topical formulation would be to maintain the stability of these antioxidants. (4) As consumers become more aware about the use of 'questionable' organic solvents, often used for the extraction of many phytochemicals, and legislation becomes more and more restrictive, safer and more efficient extraction procedures that guarantee a pure plant extract or plant-derived compound should be investigated. Further research on the use of SCFE, either to extract or purify high-value plant compounds such as phenolics or vegetable oils, might cover this need.
Undoubtedly, pharmaceuticals and cosmetics derived from food-processing by-products might represent an important, innovative and rapidly growing part of the overall food market. However, their design, i.e. their complex matrix and their composition of bioactive principles, requires careful assessment of potential risks that might arise from isolated compounds recovered from by-products. In any case, the protection of the consumer must have priority over economic interests, and health claims need to be substantiated by standardised, scientifically sound and reliable studies.
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