Colonizing Taxa (Weeds) as Sources of Natural Pigments and Dyes

Partha P. Choudhury and Nimal R. Chandrasena

Keywords:

Weeds, Plant dyes, Pigments, Chemical dyes, Anthocyanins, Carotenoids, betalains, Food colourants, Indigo, Woad, Textile dyes

Abstract:

There is a growing global demand in the dyes and pigments industry for naturally-occurring pigments as substitutes for chemically synthesized pigments. This is because of increasing concern about potential adverse health effects for those involved in dye and pigment production and concerns about environmental pollution that can result from dye industries, discharging excessive and unused dyes into waterways. Naturally occurring, principal plant pigments: anthocyanins, betalains and carotenoids are much favoured over chemical dyes and pigments because of their safety to humans. Once optimized, the extraction, processing and production of plant dyes are also relatively benign from an environmental perspective. The story of human civilizations is intimately linked with colour and the use of natural plant pigments from several well-known sources. This paper provides a brief review of this historical link of plant pigments, from ancient civilizations to the present. It also provides an overview of the chemistry of the most commonly used plant-based pigments (anthocyanins, flavones and flavonoids). With examples of potentially the most useful taxa, we also explore the opportunities for colonizing taxa (weeds) to be utilized as sources of natural dyes and pigments, which can substantially supplement or substitute the synthetic dyes and pigments, currently available. There are many species to select from although only a few appear to be presently yielding commercially exploitable natural plant pigments. The global attention continues to be on the well-known species, already cultivated or harvested from the wild, while the research on newer sources is sparse and uncoordinated, except in a few countries and regions with traditional, long histories of natural pigment use. Some natural dyeing technologies have been developed by artisans and practical-minded, lifestyle enthusiasts. In searching for eco-friendly technologies to support the livelihoods of people more broadly, dyes and pigment-based industries appear quite significant. There are technological constraints to overcome but these are no more challenging that any others we face. The global outlook for an expansion of the sources of dyes from plants is favourable and the potential contribution from colonizing plants as new sources is also quite significant. Our review finds that the research related to pigments from natural sources (i.e. applied chemistry, biochemistry, pharmacology and industrial applications) is quite intense in many countries, particularly in the last two decades