Pritam Chattopadhyay, Sandipan Chatterjee and Sukanta K Sen share the biotechnological aspects of natural food colourants Colour is the most sensitive element of any commodity, as the visual appeal of products plays a huge role in enticing consumers. The colour of food indicates its freshness and safety and is a major factor in consumer choice. The artificial food colourings used earlier are now losing credibility in the wake of food safety issues. As adherence to stringent norms for safety has also become important globally, natural food colours are gaining ground. The demand for natural colours has also increased because of their health benefits. Thus, it has become necessary to explore the natural sources of food grade colourants and their potential in the industry.
 Biocolourants are colouring agents obtained from biological sources. The term ‘natural biocolourants’ indicates that the source of the biocolour is natural, whereas the term ‘artificial biocolourants’ indicates that the colourant is synthesised biologically, but can be produced chemically. Natural biocolourants differ from artificial biocolourants not only in their source, but also in their composition and physiological activity. Generally, the level of impurities is much higher in natural biocolourants, while the bioactivity of natural biocolourants is much greater than that of their chemical counterparts. The use of natural colourants in the food industry appears to have multidimensional potential. Several studies have explored the relation of food colour with the flavour detection threshold, which affects consumer susceptibility and preference. The vitality of using biocolourants can be understood in terms of their role in preserving and enhancing the appearance, colour, quality, flavour and taste of the food product. For example, in addition to its colouring property, carotene may be used in food as an essential vitamin source; betalains are a source of essential amino acids, while anthocyanins act as quality control markers for foodstuffs. Flavonoids are colourants with high pharmacological promise. Often, diets with carotenoid mixtures are recommended instead of just one particular carotenoid, because a great variability of radicals and microenvironments takes place in vivo. Therefore, a thorough review of the bio-technological potential of natural food-grade biocolourants is essential. Biocolourants in the food industry Due to innate constraints such as stability, yield and price, natural biocolourants are gaining considerable importance in the food industry. At present, the global trends in health and nutrition reveal a preference towards natural products for the food industry.  In the last few decades, synthetic additives have been severely criticised, and consumers have shown disinclination towards these products. In the 1960s, environmental activists in the US demonstrated against the use of such food additives, and this attitude has spread. Activists campaigned for the use of natural colourants, highlighting their nutritional characteristics. This has generated a worldwide tendency to use natural colourants in food products. Food-grade natural biocolourants Natural biocolourants fall under the ‘exempt from certification’ category of the FDA and EU for food use. Some of these include annatto extract, dehydrated red beet, canthaxanthin, carotene, cotton seed meal, grape skin extract, fruit and vegetable juices, etc. Annatto: The yellow to orange colour of annatto comes from the outer layer of seeds of the tropical tree Bixa orellana. The carotenoids bixin and norbixin are responsible for the yellow-orange colour. The pH and solubility of the colourant affect the colour hue: the greater the solubility in oil, the brighter the colour. Water-soluble, oil-soluble, and oil/water-dispersible forms of annatto are also available. Annatto has been used for over two centuries as a food colour especially in cheese and in various other food products. Red beet extract: Red beet extract provides a variety of colours depending on the content of the yellow compound and may also have a good flavour. It sometimes has a bluish-red colour produced by a compound known as betanin, which is stable at a higher pH range than red cabbage extract. It has no upper usage limit. It has found wide application in different food commodities, from beverages to candy and from dairy to cattle products. Carotene: Carotene is orange-yellow in colour. It is oil-soluble, but can be made into a water-dispersible emulsion. It is listed as a Generally Recognised as Safe (GRAS) compound with no restrictions on usage. Though carrots are a good source of carotene, most carotene for commercial use is now derived from algae. For example, canthaxanthin, a carotenoid, is commercially produced from the algae Haematococcus lacustris. It is used in poultry to give colour to egg yolks, also in cosmetics and foods, particularly in dairy products (cheese), confectionary (soft and hard candy), fish and meat products, fruit products, beverages, snacks, beer and wine. Cotton seed meal: Cotton seed meal is the by-product obtained after extracting oil from cotton seed. Gossypol is a fat-soluble yellow pigment that occurs in cotton seed in bound and free forms. The bound form of gossypol is combined with free amino acids which constitute a medium-quality protein feed. Grape skin extract imparts a reddish-purple colour to beverages. However, the FDA restricts its use in alcoholic beverages or in beverage bases and in carbonated drinks. Grape juice: As colourant, grape juice is available in a variety of colours: red (shades of cherry, raspberry or strawberry), purple and yellow. It gives a strawberry-red shade upon application. It is used to colour a number of non-beverage foods, including gelatin desserts, fruit fillings and in certain confectionaries. Vegetable juice: Vegetable juices, either unfermented or lactic-acid fermented, are obtained from the edible parts of one or more vegetables. Tomato juice and blends based on tomato have long been popular and account for over 90 per cent of the non-fruit juice trade. Lycopene is the principal compound derived from tomato, enlisted under the US system. Under EU legislation, lycopene (E 160d) is considered as a food additive. It is highly stable under a wide range of temperatures and pH, and hence is used as a common food colourant. It is available in liquid form or as a cold-water dispersible powder. Carrot has long been a component of tomato blends. Red-cabbage juice gives a bright pink to red colour to a product with a pH less than 4.0 and is soluble in water, but not in oil. Marigolds: The use of marigold flowers as source of food colourants has been known since the times of the Aztec civilisation. Marigold flowers are by far the most abundant natural source for commercial lutein. The anti-mutagenic activity of the carotenoids of the Aztec marigold has also been evaluated.  Corn endosperm oil: Corn endosperm oil is a reddish-brown liquid composed chiefly of glycerides, fatty acids, sitosterols, and carotenoid pigments, obtained by isopropyl alcohol and hexane extraction from the gluten fraction of yellow corn grain. It is used in chicken feed as colour additive.Paprika: Paprika is a widely used carotenoid food colourant. Paprika oleoresin is mainly extracted from the pods. It contains three main naturally occurring pigments—capsanthin, capsorubin and carotene. This combination produces a bright orange to red-orange colour in food products. Oleoresin is oil-soluble, and when emulsified becomes water-dispersible. Riboflavin: Riboflavin (vitamin B2) has a variety of applications as a yellow food colourant. Its use is permitted in most countries. Applications include dressings, sherbet, beverages, instant desserts, ice creams, tablets and other products. Anthocyanins from banana bract and Oxalis triangularis are also potential sources of food colourants. Carrot seed oil is another biocolourant that also offers nutritional benefits. Industrial applications of biocolourants Several food colourants provide benefits beyond their colouring properties. These additional applications are discussed below. Food preservatives Several natural biocolourants, including anthocyanins, also show antagonistic activity to certain bacteria, viruses and fungi, thus protecting food from microbial spoilage. Some are also active against protozoa (Leishmania brasiliensis), and insects (Calliphora erythrrocephala). Sometimes, carotenoids can act as sunscreens to maintain the quality of food by protecting it from intense light. It has been reported that corn carotenoids inhibit the synthesis of aflatoxin by Aspergillus flavus (90 per cent) and by most of the A. parasiticus (30 per cent) strains. Quality control markers In the maintenance of GMP, the level of anthocynin is used as an indicator to evaluate the quality of coloured food. Anthocyanin profiles have been used to determine the quality of fruit jams. From the anthocyanin profile, it can be easily detected, for example, that jam labelled as black cherry jam is in reality prepared from common red cherries. In addition, the adulteration of blackberry jam with strawberries can also be detected efficiently by the analysis of pelargonidin and cyanidin-3-glucoside content. Nutritional supplements Carotenoids are also used as vitamin supplements, since carotene is the precursor of vitamin A. In under-developed countries where the diet is primarily rice-based, there is every possibility of an inadequate supply of vitamin A. This leads to night-blindness and, in extreme cases, to xerophthalmia. Riboflavin is another example of natural food-grade biocolourant which is an essential source of vitamins. It is available from milk and in several leafy vegetables, meat and fish. Yellow xanthins, in addition to their potential role as food colourant, may be used as a means of introducing essential dietary amino acids into foodstuffs. Cotton seed oil is not only a colourant but also enriched with essential amino and fatty acids. The bound form of gossypol is particularly used to combine with free amino acids. A diet supplemented with cochineal colourants is recommended for hyperactive children.  Therapeutic properties In addition to several other properties, carotene shows antioxidant properties, particularly with carotenoids in paprika and annatto. Betacyanin also has antioxidant and radical scavenging properties. Red beet products may provide protection against certain stress-related disorders. Owing to their outstanding antioxidant properties, xanthophylls, particularly lutein, zeaxanthin and astaxanthin, are lucrative as health care substance, and considered as a protective agent against aging, muscular degeneration and senile cataracts. It has been established that flavonoids present in different plant products (grape, soybean, peanut, wine, tea) show good antioxidant activity, sometimes better than that of commercially available antioxidants. Allomelanins from black bean, soybean, and sesame are found to suppress the growth of tumourigenic cells in mammals. Lycopene is thought to provide health benefits, alongside its function as a colourant. It is also supposed to act as an antioxidant. Grape seed extract is the primary commercial source of a group of powerful antioxidants known as oligomeric proanthocyanidins, also generically called pycnogenol, which are a class of flavonoids. In addition to its colouring property, canthaxanthin also shows antioxidant properties. Some epidemiological studies have also shown a correlation between the consumption of chlorophylls and decreased risk of colon cancer.  The number of approved colourants for the food industry is limited. Therefore, it is important to look into traditionally used food colourants of different countries, to use as alternative sources of food-grade natural colourants. The source material for traditionally known food colourants may also be exploited in a different way. In China and Japan, Monascus pigments, obtained as fermented products of rice and bread, have been used as food colourants and as therapeutics. The red yeast Rhodotorula glutinis produces carotenoids which are used as natural food-grade biocolourants and in fish diets. However, it is not supported by FDA and EU legislation. Some approved food colourants are known by their chemical name while others are known by their sources. The biocolourants identified by their chemical name can be easily synthesised from cheaper biotechnological sources. Coffee husks and Eugenia myrtifolia fruits are possible alternative sources for anthocyanins. The Indian black plum, Syngium cumini, has been found to be a potential source of natural food-grade biocolourants.Biotechnology may soon play a crucial role in the large-scale fermentation of natural biocolourants. Even when the biocolourant is known by its source, organic farming and integrated crop management are necessary to yield food-grade products. It is also necessary to explore multidimensional applications for natural food-grade biocolourants. Technological limitations are the major bottleneck for the commercial exploitation of the source materials. Designing a proper bioreactor would help to ease the situation. Commercial production of colourants by plant cell tissue culture will be achieved only when a fully automated predictable process with advanced technology is established by the joint effort of biotechnology and bioprocess engineering. Pritam Chattopadhyay is Professor in Plant Molecular Biology Division, Department of Botany, Visva Bharati University-Santiniketan Sandipan Chatterjee is Professor in Plant Molecular Biology Division, Department of Botany, Visva Bharati University- Santiniketan Sukanta K Sen is Associate Professor in Microbiology Division, Department of Botany, Visva Bharati University - Santiniketan |
