Researchers make prickly pear powder for red food

By Jess Halliday

- Last updated on GMT

Related tags: Fruit juice, Fruit

A new study has devised an optimal process for spray drying the juice of betalain-rich Opuntia stricta, or prickly pear, so it can used as a natural red food colouring in yoghurts and soft drinks.

The fruit juice of O. stricta is a source of betacyanin pigments, which can be used as a natural red-purple food colourant. It has previously been researched for its potential in foods in liquid form.

According to Jose Maria Oban and colleagues, whose study has been accepted for publication in the Journal of Food Engineering,​ plants of the Opuntia species may present a better source of red colour over red beet. Red beet is currently approved and commercialised in the US and EU for use in dairy, ice creams, beverages and desserts.

However Opuntia-derived colours could be preferable because they represent a lower risk of microbiological contamination, have no nitrate content, are very flavoured, and are also rich in nutrients like calcium, magnesium, vitamin C and quercetin.

The research team from the Universidad Politecnica de Cartagena in Spain said the liquid colouring from the fruit was already found to be suitable for food use since it has a high colour strength, low viscosity, and high storage stability.

The new study aimed at presenting a method to obtain a powder colourant from same fruit juices by spray drying, since a format is easier to handle for some applications and not so heavy to transport as liquids. It also has high storage stability.

Variables in the spray drying process include the amount of drying aid needed, juice concentration, liquid feed rate, and drying air inlet temperature.

The optimum conditions for the O. stricta fruit juice were seen to be: juice content of 20 per cent by volume and concentration of 1.2º Brix; glucose syrup as a drying aid with at a content of 10 per cent weight by volume, liquid feed rate of 0.72 litres/hour, air spray flow-rate of 0.47 m3/hour, drying air flow rate of 36m3/hour, and inlet drying temperature of 160ºC.

The result was a powder with a colour strength of 4.0, stable when stored at room temperature for one month.

Having devised the method, the Spanish team then went on to test its use and appeal in actual food products. They concluded:

“This colourant was successfully applied in two food model systems: a yoghurt and a soft drink. Food presented a vivid red tonality very attractive for consumers that was maintained after one month under refrigeration.”

“There is an increasing interest for large-scale cactus pear fruit processing for the production of colouring foodstuffs, opening up new markets on functional foods to dairy and beverage industries,”​ wrote from the Universidad Politecnica de Cartagena.

Fermenting the juice

The same team of researcher reported in the ​American Chemical Society's Journal of Agricultural and Food Chemistry​ earlier this year that fermenting the fruit juice of O. stricta​ could produce concentrated betalains for use as food colouring.

Their technique yielded pigment recovery of 85.5 per cent, significantly higher than anything previously reported for red beet juices, which ranged from 56 to 65 per cent.

The researchers tried three strains of micro-organism to ferment the cactus pear fruit juice, with Saccharomyces cerevisiae​ var. bayanus AWRI 796 producing optimal results. A temperature of 35 degrees Celsius is reported to produce the best results in terms of sugar consumption and pigment preservation.

After this fermentation step, centrifugation was used to separate out the biomass, while the rest was concentrated under vacuum.

Sources:

Journal of Food EngineeringPublished online ahead of print, doi: 10.1016/j.jfoodeng.1008.07.013“Production of a red-purple food colorant from Opuntia stricta by spray drying and its application in food model systems”Authors: J.M. Oban, M.R.Castellar, M, Alacid, ​J.A. Fernandez-LopezJournal of Agricultural and Food Chemistry​Published online ahead of print, ASAP Article, doi: 10.1021/jf703699c "Fermentation of​ Opuntia stricta (Haw.) Fruits for Betalains Concentration"​ Authors: M.R. Castellar, J.M. Obon, M. Alacid, J.A. Fernandez-Lopez

Related topics: Science, Flavours and colours

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