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Scientists look to cactus pear for natural yellows for food

By Stephen Daniells , 13-Jun-2006

Natural, water-soluble orange and yellow food colourings from cactus pear could offer "a new valuable source of colour preparations" say the German scientists working on bringing the pigments from the lab bench to industry.

Confronted by growing consumer demand for natural and healthy foodstuffs, food makers have increasingly been looking for alternatives to artificial food colours such as Sunset Yellow, Tartrazine and Quinoline Yellow.

And a team of researchers from Hohenheim University are currently working on extracts from cactus pear that are rich in betalains, the class of compounds almost exclusively exploited from red beet, that could soon be colouring a wide range of foods, from desserts to instant meals.

Corresponding author for the study, Florain Stintzing, told FoodNavigator.com that although colours from red beet were currently ten times cheaper, the red beet had several disadvantages, including unfavourable flavour components, no nitrate accumulation, and the risk of microbe carry-over from the earth. Cactus pear also offers other colours, like orange and yellow.

"There are not too many natural water-soluble yellow colours, especially with a low flavour impact," said Dr. Stintzing.

The results of the new study, published on-line in the journal Innovative Food Science and Emerging Technologies (doi:10.1016/j.ifset.2006.04.003), looked at the production of both coloured fruit powders and fruit concentrates from cactus pear at both lab- and pilot plant-scale.

The researchers found that by processing fresh fruit rather than frozen fruit, the process became more economical.

Pilot plant processing, using a three-stage column evaporator to concentrate 50 kg of filtered juice, produced two concentrates: semi-concentrate (33 per cent) and final concentrate (65 per cent). The concentrates were then rapidly cooled to zero and then minus 26 degrees Celsius, prior to powder production by spray drying.

"Acceptable overall pigment retentions of 71 to 83 per cent combined with the retention of the initial colour properties after reconstitution of semi-concentrated and concentrated preparations, proved the viability for industrial cactus pear juice processing," wrote lead author Markus Mosshammer.

Some non-enzymatic browning due to advanced Maillard reactions was observed, although described as the scientists as 'slight'. Minor 5-hydroxymethylfural (HMF) production was observed (2 mg per litre), but well below the limit set for fruit juices (20 mg per litre). HMF is acknowledged as an indicator to the extent of heat treatment of glucose in acidic conditions.

The pigments from the cactus pear could be used in a wide range of final food products, say the researchers, ranging from fruit and cereal bars to meat substitutes, although it is chiefly considered for blended drinks since the fruit do not carry a strong flavours.

No industrial partner is currently on-board, but Dr. Stintzing said that the interest was there and that one of the next steps was to get into contact with industry to further develop the process.

The Hohenheim team also plan collaborations with breeders of cactus pear to increase the colour in the fruit.

Concerns about the sustainability of the crops are unfounded. "Enough acreage is available," confirmed Dr. Stintzing.

The main limitation for commercialisation at this moment appears to be the current market prices of the fruit, but may be economical as a functional ingredient since the concentrate is also rich in amino acids, calcium, magnesium, and moderate levels of vitamins.

Market figures confirm the trend. While the European colouring market faces an annual growth rate of just 1 per cent between 2001 and 2008, the colouring foodstuffs market is ripping ahead on growth of 10 per cent to 15 per cent.

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