Research & Reviews: Journal of Agriculture and Allied Sciences
MenuISSN: E 2347-226X, P 2319-9857
ISSN: E 2347-226X, P 2319-9857
Department of Floriculture and Landscaping, HC & RI, Tamil Nadu Agricultural University, Coimbatore-3, Tamil Nadu, India.
Received: 01/06/2013; Revised: 07/06/2013; Accepted: 19/06/2013
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Man has always been interested with colours. The mother earth has rewarded us with natural vibrant hues called natural dyes. Natural dyes has their age old usage in textile industry and due to their non toxic and eco friendly nature find their use in food, drugs and cosmetic industries. Though earth is bestowed with plants containing a wide range of attractive and eco friendly pigments only 0.5 % has been exhaustively used and the remaining is left unexploited. Despite centuries of interest in natural pigments, our knowledge of their sources from plants, distribution, availability and properties is limited. But in recent times the environmental awareness about health hazards cause by synthetic dyes has regained importance of natural dyes. Therefore, novel plant pigments must be searched and proper collection, documentation, assessment and characterization has to be done. In this article we briefly review the availability of natural dyes (reference to India), extraction, its application in various industries, advantages, disadvantages, prospects and future thrust.
natural dyes, plants, extraction, implications
If "Colour is Life", could it be that "Natural Colour is Natural Life" ? …..Up to you, …!! Diversities can be found in the flora and fauna of the world due to its cultural and geographical variations. These plants are treasure house of many natural products. One such nature’s reward is vibrant natural dyes. Till half of 19th century- natural dyes were used to dye textiles, leather, furs, hairs, feathers, matting, basketry, bone and ivory. In 1856 William Henry Perkin (Germany) accidentally discovered “Mauveine”. Advent of synthetic dyes competes and completely replaced natural dyes within a century. But slowly suspection of synthetic dyes reported to be not eco friendly. Ironically Germany in 1996 was the 1st country to ban the use of azo dyes. On the other hand, natural dyes went on being used in some parts for aesthetic value. World which is more conscious towards ecology and environment nowadays , there is greater need today to revive the tradition of natural dye and dyeing techniques as an alternative of hazardous synthetic dyes [2]. In this article we discuss the history, need for natural dyes, types of natural dyes, principles, production technology and its implication in various industries, advantages and limitations, future thrust, prospects and conclusion.
History
From time immemorial, color has been an important criterion for acceptability of products like textiles, cosmetics, food and other items [14]. Primitive men used dye stuff to colour animal skin and their own skin during festival times. He believed that colour gave them magical power and protected tem form evil spirits and got them victory during war [16]. While there no precise date for the earliest human use of colour in Europe, it was practiced during the Bronze Age. The earliest written record of the use of natural dyes was found in China dated 2600 BC [8]. Henna was used even before 2500 BC, while saffron is mentioned in the Bible [7]. India is also fore runners in dyeing and dyes were in use during Indus Valley period (2500 BC), Mohenjo-Daro and Harappa civilization (3500 BC) and this was substantiated from findings of coloured garments of cloth and traces of madder dye ruins [1]. In Egypt, mummies have been found wrapped in colored cloth. The cochineal dye was used by the people of Aztec and Maya culture period of Central and North America. By the 4th century AD, dyes such as woad, madder, weld, Brazil wood, indigo and a dark reddish-purple were known. Brazil was named after the woad found there. Colonists and settlers discovered that indigenous dyers used what was abundant including minerals, bodily fluids of animals, plant materials including leaves, bark, roots, lichens, berries, soot, and soil which provided dyes and pigments of purple, black, ochre, red, and yellow. The well known ancient dyes include red dye from roots of Rubia tinctorum L., blue indigo dye from leaves of Indigofera tinctoria, yellow dyes from stigmas of saffron (Crocus sativus ) and rhizome of turmeric (Curcuma longa). Dyeing might be an accidental happening but the need of dyeing become very common in human life. So the art of dyeing spread widely as civilization advanced. Today dyeing is a complex and specialized science. Natural dyeing is practiced as a unique feature by crafts man and synthetic dyeing only is commercially followed.
Need for natural dye
Natural dyes went on being used and are still used traditionally by artists because of their different and aesthetic colouristic value, symbolic powers and therapeutic functions and green mined consumers priority for organic food with natural colours. Natural dyes are regaining its importance in global society because of growing awareness of the threats on natural environments worldwide. In last few decades, synthetic dyes have been severely criticized and consumers show reluctance towards these products, consequently they prefer to use the natural colorants [6]. Because of health and hygiene, nutrition, pharmaceutical activities, fashion and environmental consciousness, indicate relative dependency on natural products. Besides good market value fetched by the natural colored products and as of now, natural colorants have become the major alternatives to synthetic colorants [4].
Advantages of natural dyes
Natural dyes have wide viability and huge potential. Natural dyes are non toxic, non polluting, non carcinogenic, non poisonous and environmental friendly. They produce harmonizing colours, gentle, soft, lustrous and subtle creating restful. Many are water-soluble facilitates incorporation into aqueous food systems which make the qualities of natural food colorants attractive. Since the natural dyes are polygenetic nature specialty and rare colour ideas is possible by mix and match system. Along with aesthetic value and quality natural dyes also have potential positive health effects like antioxidant properties. No reports of health hazardous and are anti inflammatory, anti allergic and radiation-protective.
Limitations of natural dyes
Bio colorants have several potential benefits yet their collection extraction procedures are tedious with low colour value. The natural dyes cost higher than synthetic dyes and are instable during processing etc., It is difficult to reproduce shades because this agro product is based with season, place species and maturity period etc. Nearly all-natural dyes with a few exceptions need mordants to fix them. This takes a larger dyeing time and excess cost for mordants and mordanting. Post-harvest processing and handling is cumber some. Scientific back up of the science involved in natural dyeing has not yet been completely explored. Also natural dyes do not perform well with artificial fibers. Problems in food industry is instability during processing because of sensitivity to temperature, oxygen, light and pH Natural dyes are decolourised or degraded during storage. These disadvantages make hinder their popularity.
Natural Dyes
Natural dyes can be defined as those colorants (dyes and pigments) obtained from plants, animals or minerals. They attach to the substrate by physical adsorption, mechanical retention, and formation of covalent chemical bonds or of complexes with salts or metals, or by solution. Natural dyes can be subdivided into dyes and pigments. Dyes lose their crystal structures during application by dissolution or vapourisation and are often used for textile (dyeing) and food colourants (staining). Pigments retain their crystalline or particulate structure throughout their application. Pigments are used in inks, paints and cosmetics.
Principles of dyeing
Plants in nature produce so many colours for so many reasons. Most plants are green (most ubiquitous colour) to capture light energy and converts to chemical energy for preparing food. Also plant produce multi colour flowers, fruits to attract insects, protection from pest and diseases. Along with this plants are able to yield dyes from this colour. Pigmentary molecules in natural dyes present impart colour. Pigmentary molecules are aromatic ring structure coupled with a side chain. This forms a Chromogen-chromophore with auxochrome. Chromogen chromophere is the aromatic structure containing benzene, naphthalene or anthracene rings. Chromogenchromophore structure is not sufficient to impart solubility and causes adherence of the dye only in presence of auxochrome - important for bonding affinity groups [15]. Most of the natural dyes have no substantivity on cellulose or other textile fibers. The majority of natural dyes need a mordanting chemical (preferably metal salt or suitably coordinating complex forming agents) to create an affinity between the fiber and dye or the pigment molecules. After mordanting, the metal salts anchoring to the fibers, attracts the dye/organic
Mordants
A mordant is a binding agent that adheres well to both the fibers and the dye. Usually chemical mordants are used with restrictions to heavy metals and carcinogenic chemicals. The permissible levels are As (1ppm), Pb (1ppm), Cd (2ppm), Cr (2ppm), Co (4ppm), Cu (50ppm), Ni (4ppm) and Zn (20ppm). No upper limit on Al, Fe and Sn.
Natural dyes from plants
Many natural dye stuffs are obtained from plats like red, yellow, blue, black, brown and combination of these (Table 1). Amazingly plants produce nearly 2000 pigments out of which some 150 pigments have been exploited. Many of the plants used for dye extraction are classified as medicinal and some have shown anti microbial activity. Table 2 & 3 illustrates the traditionally used dye yielding plants which yield pigments and have medicinal values.
Table 1: Sources of different coloured dyes and mordants [17]
Table 2: Important dye-yielding plants with pigments.
Table 3: Dye-yielding plants with its medicinal value
Ethical dyeing manifesto
The Earth sustains us all - Treat her with gratitude and respect. Greed should not govern us - We need to give back what we take. The clauses for ethical dyeing 1. To not use synthetic chemicals at any stage of the dyeing process 2. To conserve the sources of natural dyes by not consuming the roots, heartwoods or barks of perennial trees as dye material. 3. To avoid the use of plant materials that is food to man and animals. 4. To minimize the use of (plant organs that propagate a species) flowers, seeds, fruits gathered from the wild. 5. To cultivate the required dye plants.
Preparation of dyes
Gather sufficient dyestuff (plant material) to fill a bucket or pail. Chop or shred if bulky. To facilitate pigment extraction, press the dyestuff down and add sufficient cold water to cover. Use a rock or a heavy plate to keep the mass immersed. Set aside 24 hours. If local water is contaminated with minerals such as iron, a substantial color shift may occur. Iron is a common mordant used by dyers. If local water is not pure, distilled or deionized water can be used to avoid the color shift. Bring the dyestuff and soaking water to a boil (98–100°C.) (Some dyestuffs are heat sensitive and require a lower temperature for extracting the dye from the dyestuff. The heat sensitive dyes are often found in flowers. A temperature of 70–80°C is usually effective for extracting the dye from flowers.) Maintain the temperature over heat for 1–2 hours depending upon the bulk of the dyestuff and the time needed to render it completely limp. (There will be some evidence of color in the “dye liquor” by this time). Once done, set the contents aside. When liquid are cool to the touch, strain the cooked dyestuff Allow the wet dyestuff to drip for several hours. Save all of the liquid as this constitutes the “dye bath” [3]. To the dye bath or dye liquor add the textile. Raise the heat to a slow simmer (90–92°C) (or 70–80°C for the heat sensitive floral dyes). Maintain this temperature for 15 minutes and then reduce to 60°C and process another 45 minutes. Remove and cool the contents to room temperature.. Remove the textile. Drain or squeeze out remaining dye liquor. Shake and then hang to dry in the shade.
Extraction Technology
Extraction technology is done in many ways like aqueous extraction system - Material-to-liquor ratio (MLR), Solvent Extraction system, Super critical fluid extraction system, Microwave assited Extraction technology, Continuous steam distillation method. While purification includes filtration or reverse osmosis or preparatory HPLC and drying of the product may be by spray or under using vacuum or freeze drying technique.
Potential use in industries
The natural dyes can be used for coloration of the product in food industry, pharmaceuticals industry, textile industry, leather industry, cosmetics industry.
A. Textile industry - Dyes can be used for colouration of textile material like yarn, silk wool fabric and applied on the apparels. Common dyes used are annatto, indigo, harda kamala. Natural dyes are substantive and require a mordant to fix to the fabric. The Colours of Nature (TcoN) is one of only few remaining natural dyeing units in the world, entirely focused on an environmental friendly, vegetable dyeing process and research. The unit is specialized in the natural indigo fermentation Process. The products should be organic and grown without the use of pesticides and fertilizers. Production methods are environment-friendly and do not pollute the environment and practice water conservation. Water used is stored after each step of the dyeing process and recycled for agricultural use. Alum, a non-polluting mordant is only used to fix the colours. Materials which have beneficial effects like Tannin (mordant) - Powerful antiseptic, Turmeric - revitalises the skin; Indigo - Cooling sensation and relaxing are used in the dyeing process.)
B. Food and confectionery industry - Most common dye used for coloration of the edible items are annatto seeds, The water soluble extract are used for coloration of butter while oil soluble extract are used for colouration of ghee & ice cream, etc. Producers of confectionery, soft drinks, alcoholic beverages, salad dressings and dairy products are the most significant users of natural colorants. Currently 43 colorants are authorized as food additives by the Council of the European Union. Juices or extracts from some fruit and vegetables are used for coloring purposes. The Food preservatives have antagonistic activity against micro organisms. Norton [12] reported that corn carotenoids inhibit the synthesis of aflatoxin by Aspergillus flavus (90%) and by most of the A. parasiticus (30%) strains. Quality control markers are anthocyanin profiles used to determine the quality of fruit jams like adulteration of black berry jams with straw berries by pellargonidin test. As nutritional supplements bio colurants possess “vegetable principles” (biological active source). These are sources for obtaining drug substances (biologically active) and many other natural compounds used in various industries such as food, pharmaceuticals, cosmetics, with important commercial value [5]. Carotenoids are also used as vitamin supplements [9], since β-carotene is the precursor of vitamin A.
C. Pharmaceutical and Therapeutic industry - Natural colourants also play an important role in human health because they contain some biologically active compounds, which possess a number of pharmacological properties like strong antioxidant, antimutagenic, anti-inflammatory and antiartheritic effect [10,11]. Carotenoids also act as biological antioxidants, protecting cells and tissues from the damaging effects of free radicals and singlet oxygen and also as a good source of anti-tumor agent [18]. Grape seed extract is the primary commercial source of a group of powerful antioxidants known as oligomeric proanthocyanidins (OPCs), also generically called pycnogenol, a class of flavonoids [4]. Also bio colourants are used to colour pills and tonics [13].
D. Cosmetic industry - Dyes derived from plants like Bixa orellana and Lithospermum erythrorhizon serves as sources for colouring lipstick and eye shadow liners
E. Leather industry - Vegetable tannin are used for tanning the leather, Walnut bark, eucalyptus bark, turmeric rhizomes and tea leaves commonly used, confined to cottage and small-scale leather units while large units use Chrome Tanning.
Future thrust
Optimization of the selection, cultivation and extraction process of the major “historical” dye plants, improving the quality and yield of natural dye substances is likely by understanding the physiological and agronomic factors affecting the quality and yield factors plant. To improve the quality and yield by selection, conventional breeding, and by genetic manipulation and transformation is needed. We have to develop efficient systems of dye plant production (eg, nutrition, pest, weed and disease control, husbandry, suitable rotations and soil type. Researching “new” sources of natural dyes from local sources is necessary. Waste products from dye plant exploitation should be diverted for other uses, like food or timber.
In essence, the message to consumers that "Natural is Better" is gaining popularity day-by-day. Although, natural colors are on the rise but they are unlikely to be a total replacement for synthetic dyes because the area of land required for production of natural colourants, yielding plants increasing due to inadequate strategies and horticultural practices on this crops. Thus, natural dyes is likely to occupy a small niche market, unless technology of horticultural practices and pigments extraction is redefined and standardisation on modern scientific lines.