Stability and capability, challenges with natural coloursLynda Searby finds out how nano-entrapment, co-pigmentation and accelerated stability tests could help to make natural colours nice rather than nauseating to work with. Beverage or ice cream? Furthermore, colourings within the same colour group do not always behave in the same way. Take for example, the two anthocyanins elderberry and blackcurrant. “They are a very similar colour but one is far more stable than the other,” explains Beck. “So, say you are formulating two products: a beverage that will sit on shelf for six months in a transparent bottle and an ice cream product, even though the pH of the two products is similar, they would need different colour solutions - elderberry would be stable enough for the ice cream but not for the beverage.” Besides being prone to oxidation, carotenoids are not water soluble. Several academic institutions, among them Louisiana State University, are currently researching nano-entrapment as a possible solution to this issue. “We set out to develop a nano-structure made from food-grade ingredients that could be used to entrap beta carotene,” explains Cristina Sabliov, associate professor, Biological & Agricultural Engineering Department, Louisiana State University. “Beta carotene is hydrophobic but when you put it in alginic acid cross-linked with calcium it forms nano-structures that are readily soluble in water, so they disperse well, forming a uniform orange colour.” Many academic discoveries never actually make it into the commercial arena, but Sabliov says this technology is ready to be used as soon as industry requires it. “I haven’t done an economic analysis of the structure but it can be scaled up easily and the ingredients are ones the industry already uses – not expensive polymers.” Nano-entrapment might be the most cutting-edge solution to the carotenoid water solubility problem, but it isn’t the only solution. Several colour suppliers have already developed water dispersible carotenoids using emulsification. So what does nano-entrapment offer that emulsification doesn’t? “Nano-entrapment provides better physical and chemical stability for the ingredient, so with beta carotene, for example, it means you may be able to avoid oxidation,” says Sabliov. But not everyone agrees that nano-entrapment is superior to conventional emulsification. Beck argues that nano-entrapment could have a negative impact on stability because the smaller particle size creates a larger surface area to be oxdised. Anthocyanins are the polyphenolic pigments responsible for the red to blue colour in a wide range of fruit and vegetables, including purple sweet potato, elderberry, black and purple carrot and red cabbage. However, they are unstable at high pH values, and will change from blue at pH 7 to red at pH 3, making it difficult to create a naturally coloured blue, purple or green beverage with an acid pH. Stable blue colouring Chr. Hansen claims to be the only company to have developed a stable, natural blue colouring for a range of applications for the European market. “Blue was a challenge a few years ago but we have solved this issue,” says Lionel Schmitt, VP commercial development in Chr. Hansen's colour division. “Our patented Blue WSS-P product, based on anthocyanins, remains the only approved blue colour solution on the EU market.” Even so, the colour is limited to the pH range 5.5 to 8 and applications such as dragees, jelly confectionery, ice cream and icing. Wild Flavors Inc, meanwhile, a company allied to Germany-based Rudolf Wild, has developed an acid-stable, naturally-derived blue colour, which is manufactured from fresh fruit. “The current FDA-compliant blue colour additives are only stable when applied in neutral pH products (pH 5.5-7),” says Hélène Möller, ingredients product manager at Wild. “Wild is the first in the USA to provide a naturally-derived blue colour additive that is suitable for most food and beverage applications.” Unfortunately for European manufacturers, the colour is not yet approved for use in the EU. A potential new source of blue pigments for the food industry could be the microalgae Haslea ostrearia, which is responsible for the greening of oyster gills. The compound, called marennine, was the focus of a French study published in the Journal of Agricultural and Food Chemistry in July 2008, and is said to show high water solubility, high resistance to heat and light and stability at the pH range 6 to 8. Meanwhile, Professor Cathie Martin, group leader of the Department of Metabolic Biology at the UK’s John Innes Centre, believes one answer to creating stable natural blues could lie in co-pigmentation. “Anthocyanins can be stabilised through complexing with other compounds,” she says. “We’re doing research in this area because you can get some really quite exciting colours which are more in the blue spectrum.” Part of the reason she believes there is little known about co-pigmentation is that sometimes the molecules that can co-pigment are not in the same compartment of the plant cell as the anthocyanins, and it would require systematic testing of molecules to identify ‘compatible’ molecules. Through her work she has been able to produce an indigo colour that is a combination of flavonols and anthocyanins. While Martin’s work is purely academic, there are colour manufacturers, such as DD Williamson, who are complexing different anthocyanins to achieve more stable colours. Sources of anthocyanins “The chemical structure of anthocyanins varies depending on whether they are sourced from fruit or vegetables,” explains DD Williamson food science chemist Jody Renner-Nantz. “Vegetable sourced anthocyanins are acylated which makes them more stable, whereas fruit sourced anthocyanins are non-acylated, which means they are less stable. If you combine fruit and vegetable based anthocyanins, the vegetable compounds will protect the molecule from degradation over time.” Besides anthocyanins, cochineal extract/carmine and betalains are widely used in the red-purple range. Cochineal extract/carmine is a red colouring that is heat, pH and light stable. Betalains, by contrast, offer poor heat and light stability, and are most stable at pH 4-5.5. They are currently produced from the source that makes the most economic sense - red beet, although other sources are being explored. Researchers at Hohenheim University, for example, have examined the potential of betalain-rich extracts from pitaya and cactus pear. However, the market price of the fruit is the main limitation to its commercialisation as a colour. The regulatory climate is also a barrier to introducing new natural food colours onto the European market. To be authorised for use, a natural colour must be approved as an additive and assigned an E number. Colouring foodstuffs do not have to follow the same procedure as they are classed as food ingredients, not additives. This distinction makes it easier for the industry to bring to market new colouring foodstuffs and is contributing to a rise in their popularity. “We’re seeing food and beverage manufacturers in Europe using colouring foodstuffs in lieu of natural colours,” affirms DD Williamson’s Renner-Nantz. “The colouring foodstuffs segment is very promising,” agrees Schmitt at Chr. Hansen, which last year added eight new natural colouring foodstuffs to its FruitMax range. “Colouring foodstuffs appeal to health-conscious consumers who increasingly prefer food with natural ingredients. With colouring foodstuffs there is a clear link to nature. The solutions are processed from fruits, vegetables, herbs and spices.” Wild, meanwhile, has developed seven new colouring foodstuffs: banana, mango, mandarin, redcurrant, elderberry, strawberry and lime. These are natural extracts and concentrates from plants, fruits and vegetables and are said to be especially suited to use in ice cream and confectionery such as hard candies, dragees and jelly gums. Industry has come up with solutions to many of the technical challenges posed by natural colours – emulsification and encapsulation systems for water insoluble colours; processing aids which prevent oxidation and smaller particle sizes which give more vibrant colours by maximising light reflection. However, solving the challenges that remain will require closer collaboration between industry and academia and acceptance of approaches like nano-technology and genetic modification. Annie Teoh, Cathie Martin and Cristina Sabliov will all be speaking at Fi Conference’s Innovations in Natural Colour, London, 25-26 February 2010. www.ficonferences.com/colour | ||||||||||||||||||||
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