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Maintaining colour stability
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Saturday, 18 November, 2006, 08 : 00 AM [IST]
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ines whether the consumer accepts or rejects the product. Adding colour to foods can encourage acceptance by offsetting colour loss caused by exposure to light, temperature extremes and/or moisture; correcting natural colour variation; enhancing naturally weak colours; providing a colourful identity to products that would otherwise have little colour (e.g. gelatins); and supplying a fun look to kid-oriented beverages and candies. Added food colours can be temperamental, influenced by factors like the product matrix and processing and/or storage conditions. Keeping attractive hues from turning into ho-hum or dingy shades requires a blend of food science, ingredient technology and packaging.
Colour categories
Food and beverage designers can choose from a wide array of synthetic and natural colourants to give their products the expected appearance. As per the FSL Colour additives permitted for foods and beverages are Brilliant Blue FCF, Indigo Carmine, Fast Green FCF, Erythrosine, Ponceau 4R, Tartrazine & Sunset Yellow. Colour suppliers provide these synthetic colours as water-soluble dyes and water-insoluble lakes. Lakes, formed by extending dyes on an aluminum hydrate substrate, colour by dispersion and are useful in products containing fats and oils, or in products with insufficient moisture to dissolve dyes. Colour additives also consist of what are called natural and nature-identical colours. Natural colours are derived from natural sources like vegetables, minerals and animals. They include carotenoids (yellow to red), caramel colour (light yellow to dark brown), turmeric (yellow), annatto (yellow to reddish orange). Nature-identical colours are produced by chemical synthesis and are considered chemically and functionally identical to the same colourant found in nature. Even with this comprehensive palette, achieving the desired colour in foods and beverages is not a simple task.
Environmental elements
Every food and beverage reflects a unique blend of ingredients, chemical attributes (e.g., acidity), processing conditions and packaging. Colourants vary in their ability to function within these diverse elements.
pH:
At certain pH levels, some colourants degrade or shift to a different, less stable colour. Most synthetic dyes have good low-pH stability; however, Erythrosine will precipitate at a pH less than 4.0. "Lakes are stable at a pH between 4.0 to 8.0, but outside that range, a lake's substrate typically breaks down, releasing the dye and causing colour migration," says Karen Sharma, application development manager.
In the natural colours, annatto will precipitate at a pH less than 4.0; however, these colourants can be used in acidic applications by modifying their form. For instance, an annatto emulsion resists precipitation at low pH Natural colours with good pH stability include caramel colour (pH 3 to 10), the carotenoids (pH 2 to 8) and turmeric (pH 2.5 to 8). Some caramel colours change colour strength as the pH increases. Candy made with a panned sugar coating demonstrates how the pH of a product can impact colour choice. Sugar inversion, which several factors - including low pH-might induce, can cause improper coating crystallisation, producing a rough surface. "To prevent sugar inversion, the pH of the coloured syrup typically should not go below 4.5." According to Lewis, food technologist, Colourcon, "Synthetic colours are often used for panning, since it is easier to get a stable, uniform colour than with natural colourants."
Ascorbic acid:
Some synthetic colours, such as Tartrazine, Sunset Yellow contain an azolinkage, two nitrogen atoms with a double bond in between. Ascorbic acid can break this bond, causing the colour to fade. On the plus side, ascorbic acid is an oxygen scavenger and helps prevent the fading of colours like carmine and beta carotene.
Ascorbic acid is mainly an issue in beverages, especially those fortified with vitamin C. Solutions include using encapsulated ascorbic acid or natural colourants other than the anthocyanins.
Heat:
Both synthetic and natural colours generally have good heat stability, in particular Erythrosine,Brilliant Blue FCF, Indigo Carmine, caramel colour, & turmeric. A colour's ability to withstand heat is dependent on end product processing conditions, specifically the temperature, time and point of colour addition.
Light:
All colours, both synthetic and natural, will eventually fade if exposed to sufficient light. Colourants especially susceptible to light include Erythrosine and turmeric, while annatto, has moderate to good light stability.
Approaches to minimising light degradation include colour encapsulation or emulsions, packaging materials with UV barriers, and shelf-life management. "While the colour turmeric can fade in days or weeks in the presence of light, an encapsulated form of turmeric can have a shelf life of a year or more. Erythrosine, often required to achieve shades of hot pink and purple is widely used in products like cereals and candies that are packaged in opaque metalised films or other light inhibiting materials.
Oxygen:
Colourants like carmine, carotenoids and paprika can fade in the presence of oxygen. Antioxidants like can improve the shelf life of the colour itself and help maintain the desired shade in the end product.
Matrix maneuvers
Effective colourants not only supply consistent hues, they also disperse evenly in a product without bleeding or precipitating out over time. Colour stability can be affected by the moisture, protein or fat content of the end product. Some colourants are naturally more stable in certain product matrices, plus pigments can be prepared in a variety of forms that ensure uniform and stable dispersion in diverse applications. While moisture is key to the consistent dispersion of water-soluble colours in food systems like beverages and fruit fillings, available water can have a detrimental effect on the colour stability of some products. For example, a multilayered dessertmade with water-soluble colourants might experience colour migration between the layers. "Lakes are commonly used to prevent colour migration in higher-moisture systems, plus they are useful in dry mixes like snack seasonings, or if there is insufficient moisture to dissolve water soluble colours, such as cookie fillings. Indigo Carmine is not stable in the liquid form or in products with high water activity; however, it works well in products with low water activity, like confections and cereals." Beet colour will degrade with moisture - as well as heat-and is not recommended for beverages and fruit fillings. It is an effective colourant in products like dry beverage mixes and frozen novelties. Some high-moisture applications might require an oil-soluble colour to achieve the desired hue. A uniform dispersion can be attained by modifying the colour form. "Beta carotene, which is naturally oil-soluble, can be made into a microemulsion that disperses evenly in water. In a beverage, the microemulsion provides a clear, natural yellow colour that will not separate and form a ring at the top. Product designers also need to remember that proteins have different colloidal charges. If a caramel colour has a charge opposite the protein in the system, it may form a precipitate. To prevent this, caramel colours are available with different charges for specific applications." For example, soft drinks generally carry negatively charged particles due to tannins derived from plant material, root, bark, etc. Using a negatively charged caramel colour pr
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