Star fruit could offer inexpensive source of antioxidants

Residues from star fruit, a waste product from the juicing process, is a rich source of extractable antioxidants, says research from Singapore.

Star fruit (Averrhoa carambola L.), also known as carambola, are grown extensively in Southeast Asia, Australia, South America, Hawaii and Southern Florida. Sales of star fruit from Florida were estimated at $17.1 m in 1996.

"An increasingly growing market for nutraceuticals and functional foods has triggered the study on natural sources of antioxidants and their potential for nutraceuticals and functional food," said Guanghou Shui and Lai Peng Leong from the National University of Singapore.

The new study, published in the journal Food Chemistry (Vol. 97, pp. 277-284), looked at methods of extraction, identification and activity of the antioxidants found in the star fruit.

The scientists used acetone or ethanol as extraction solvents with different ratios of water, and concluded: "The optimum conditions used for extraction were 50 per cent acetone as extraction solvent at 90 degrees Celsius for 45 minutes,"

The average yield of polyphenols was found to be 33 milligrams per gram of residue, which accounted for over 70 per cent of the total polyphenol content of the whole fruit.

The Total Oxidizing Activity (TAA), measured using the ferric reducing/antioxidant power (FRAP) assay was measured at 510 micromoles per gram, which showed that "residues from star fruit were excellent sources of phenolics antioxidants."

The major antioxidant present in the extract was found to be proanythocyanidins, most notably (-)epicatechin, an antioxidant more commonly associated with green tea and red wine.

"This suggests [star fruit has a] great commercial potential as a nutraceutical resource or functional food ingredient. Further research is necessary to understand its proanythocyanidin profiles and possible dietary intake of these compounds," concluded Shui and Leong.

The US antioxidant market was estimated to be $370m in 2005.

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