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Star fruit could offer inexpensive source of
antioxidants

By Stephen Daniells

3/7/2006 - 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.