Soy isoflavone could be edible oil antioxidant, suggests study

By Stephen Daniells

- Last updated on GMT

Related tags Antioxidant

The soy isoflavone, genistein, could act as an antioxidant to
prolong the shelf-life of bulk edible oils, suggests a study using
linseed oil.

"The findings raise interest about the ingredient functionality of genistein as an antioxidant, which could increase its utility and applicability in food systems far beyond its current use as a nutraceutical additive,"​ wrote lead author Ted Russin in the Journal of Food Science​ (doi:10.1111/j.1750-3841.2006.00111.x).

The use of natural alternatives to synthetic preservatives, such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT), to slow down the oxidative deterioration of food is gaining interest.

According to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts, tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by easier consumer acceptance and legal requirements for market access.

This natural antioxidant range could potentially include genistein, according to promising results from scientists from Agriculture and Agri-Food Canada, who prepared four linseed oil solutions: linseed oil; linseed oil containing 2 micromoles of genistein per gram of oil; linseed oil containing 4 micromoles of genistein per gram of oil; and linseed oil containing 200 ppm BHA.

The researchers used dimethyl sulfoxide (DMSO) (1.7 per cent) to promote the solubility of genistein. The DMSO also acted as a pro-oxidant.

Linseed was chosen because it is highly unsaturated and facilitates the rapid autoxidation under minimal oxidative stress, said the researchers. By heating the oils at 60 degrees Celsius, results could be generated that reflect the mechanism of oxidation that occurs during standard storage conditions.

Two techniques were use to quantify the antioxidant activities were analyzed using 2 techniques: peroxide values (PV); and Fourier transform infrared attenuated total reflectance (FTIR-ATR).

For both these techniques, Russin and his colleagues calculated the so-called induction points (IP), which is a measure of the onset of oxidation and spoilage of the oil.

The shortest IP was measured for the linseed oil without any antioxidant added (17 hours for PV, and 36.9 hours for FTIR). The longest IP was observed for the linseed oil with 200 ppm BHA added (39.9 hours for PV, 54.2 hours for FTIR).

The two genistein-linseed oils had intermediate IP values, report the researchers: The 4 micromoles of genistein per gram of oil performed better than the 2 micromoles of genistein per gram of oil, but the difference was not significant, said Russin.

"Although genistein was not as effective as BHA in retarding oxidation, the results clearly demonstrate that it is able to act as an antioxidant in a bulk oil system,"​ said Russin.

The researchers said that more research is needed to determine the ideal conditions for the effective use of genistein as an antioxidant in different food applications.

"Such ingredients could potentially be used in the development of functional foods with high polyunsaturated fatty acid content,"​ they said.

Antioxidant revenues are predicted to grow from €46m ($55m) in 2004 to €58m ($70m) in 2008, according to Frost and Sullivan.

The study was financially supported by Canada-based Oleanergie F2001, a soy protein isolates and concentrates producer.

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