Natural colours, new possible applications

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Among the variety of synthetic additives used in food production to improve their aspect and sensory profile, artificial colourants have been the first towards which consumers developed a feeling of distrust and antipathy.

Food  products with unnaturally intense and bright colours could be accepted in the past, but their popularity rapidly decreased, especially on the European market. In 2007, a controversial scientific study (the “Southampton Study”) related some of them with children hyperactivity, thus contributing to their progressive abandonment; this also because the presence of these colours requires a specific warning (compulsory in Europe) on the label. Moreover, EFSA recently recommended new safety evaluations on 6 artificial colours, 5 of which belonging to the Southampton Study: Allura Red, Azorubine, Ponceau, Sunset Yellow, Tartrazine and Amaranth. This is compounded also by the growing pressure to “clean up labels”, that is removing all ingredients and additives that are or appear  to be non-natural, favouring natural substances that are perceived as healthy and harmless. However, there are several substances, as for instance the natural colour Cochineal (also called carmine), which are no longer accepted by consumers, although being 100% natural and in use for centuries. Cochineal, frequently used to enhance the red colour of beverages and confectionery products, is made from the raw dried and pulverised bodies of insects of the specie Dactylopius coccus and Kermes vermilio species, or, more recently, from microorganisms bioengineered to produce carminic acid (responsible of the colour). The refusal of this natural colour goes beyond the needs of people with allergies or vegetarians and vegans, so much so that, further to an on-line petition signed by more than 6000 consumers, an important brand as Starbucks decided to replace it with lycopene in its strawberry-flavoured foods and drinks. Another natural red colour enjoys a higher level of agreement: Annatto, derived from the seeds of the achiote trees (Bixa orellana). This liposoluble pigment is particularly suitable for extremely fat food products, as butter, margarine, cheese, ice-cream, and desserts, but also for liqueurs, breakfast cereals, bakery products, and cake decorations. Higher agreement meet natural colours like carotenes and carotinoids (various shades from yellow to orange), anthocyans and anthocyanins (flavonoids producing pink to purple colourings), occurring in nature in the tissues of many flowers, fruits and vegetables. Other natural colours are green (chlorophyll), brown (various types of caramel) and blue (derived from flowers). Not only carotenes and anthocyanins are natural substances: they even have beneficial effects on health, especially antioxidants and provitamins. Therefore, the presence of these substances in food is generally well accepted by most consumers, especially if it is not mentioned with its chemical name, but as “carrot juice” or “beet root” extract, and so on. How come that the use of these substances in the confectionery sector and other food sectors in general is still limited, but has been spreading only in the last few years? The answer can be found in the chemical structure of this colourings, which are not very stable, especially when exposed to light, heat, and pH (Fig. 1). Carotenes and anthocyanins are often suitable for use in confectionery products (hard and soft candies, jellies, coloured confetti, etc.), because in an environment containing little water or in presence of gelling agents, the colour is stabilized.


More stable formulations
The last years have seen significant progress in the choice and transformation of molecules in more stable structures, and in improved formulations, in order to prevent colour changes during the product shelf-life. As for carotenes, formulations have been produced that are more stable to oxidation and, with suitable emulsifiers, now they can be used also in food products with abundant water contents. Carotenes and xanthophylls (other natural colours with similar structure, including zeaxanthin and lutein) can be used for colouring food products (especially egg pasta, sweets, desserts, and egg-based baked goods), even indirectly: in fact, if added to the feed of laying hens, the yolk of their eggs will have a more intense colour, reaching orange-red, resulting in finished products with a warmer and more intense colour.  While the majority of carotenes and related chemical colours are liposoluble, anthocyanins are water-soluble, and are available both as liquids and powders, in the form that best suits each food product. Carotenes and xanthophylls are derived mainly from some vegetables (as carrots, peppers and corn, as well as green leaf vegetables, where the presence of carotenes is hidden by the presence of chlorophyll), and several algae. Anthocyanins are derived from varieties of potatoes and carrots characterized by purple colours, grape skin and various berries. Anthocyanins are mainly used for red colourings, as for instance in confectionery for strawberry and raspberry flavoured products. The ideal pH, where they achieve vivid and intense colourings, is acid (from 2 to 4.5); this condition can be easily created for fruit-based sweets, which often contain acidifying substances or acidity regulators. For products subject to thermal treatments, or that are wrapped in transparent packs, the use of thermostable and photostable anthocyanins is required, failing which the product colour fades away. If no anthocyanin can produce the desired colour for specific use conditions, other natural reds are available, as carmine (Cochineal), Annatto, Betanin (derived from red beet root), Tumeric (orange colourant derived from the root of the Curcuma longa plant), or carotenes, including red lycopene (derived from tomato). Next to its health-beneficial effects, lycopene has the advantage of being stable to high pH, high temperatures and in presence of ascorbic acid, whereas many anthocyanins darken in presence of this substance.

Fig. 1. Colour changes in anthocyanins, depending on the pH

Conclusions
In one word, the sector of natural colours is undergoing a process of change and expansion (with the European market far ahead compared to the American one), in spite of several disadvantages with respect to the use of artificial colours, as lower stability and higher fluctuating costs. The correct natural colour must be selected with great attention, taking into account the type of target food and the production process; therefore, more technical assistance is required to obtain the desired result.  Producers and retailers of these colourants today are constantly researching more effective and less expensive extraction technologies, more stable formulations, and more effective colour rendering and anchoring systems, for example by reducing the dimensions of colour particles.

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