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Thus, if bioengineered natural, green dyes can be produced at a comparable price, the following
benefits will be realized:
1. Reduce the use of toxics since starting materials are environmentally benign with associated benefits in terms of waste disposal and occupational safety.
2. Production can be decentralized resulting in savings in transportation costs.
3. After extraction of the dye, the biomass can be used for energy generation (e.g., through anaerobic treatment to generate methane, which in turn, can be sued as a fuel) and the growth media can be recycled; thus, there are virtually no wastes generated.
4. Possible beneficial aspects such as higher UV absorption by the fabric (which contains natural dye) can result in reduced incidence of melanoma. It is clear, however, that if natural dyes are to be considered as an alternative to the synthetic dyes used today, they have to manifest the same characteristics of synthetic dyes as those listed above.
Specifically, the major challenges in this field are:
1. To produce natural dyes in the quantities required,
2. To produce natural dyes at a reasonable price,
3. To produce natural dyes that have high color-fastness.
The major avenues of production of green dyes are:
Extraction from plants
Extraction from arthropods and marine invertebrates (e.g., sea urchins and starfish)
Extraction from algae (e.g., blue-green algae)
Production from bacteria and fungi
Secondary Metabolites
Regardless of the source, it is believed that products which may be harnessed as green dyes are in essence secondary metabolites produced by the organism. These secondary metabolites are low molecular weight natural products that have a restricted taxonomic distribution, possess no obvious function in cell growth and are synthesized for a finite period by cells that are no longer undergoing balanced growth. However, they have specialized survival functions in nature and are observed to be numerous in organisms occupying densely inhabited environments and are believed to have a prominent role in the coexistence and coevolution of species allowing interaction within a community. Functions of secondary metabolites can be listed as follows:
1. Competitive weapons against other organisms
2. Able to chelate toxic metals present in the environment so that it is not bio-assimilable
3. Form structural and extracellular protective agents
4. Act as agents of organism-host symbiosis
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