SYDNEY - Bananas are a mainstay of the Queensland economy, worth an annual A$410 million ($513 million), but one-third of those produced are rejected by supermarkets - because they are too small, too straight or too yellow.

Now government researchers are investigating other ways to use the imperfect fruit, in order to maximise the return to growers.

Among the possibilities being scrutinised are frozen whole peeled bananas for supply to juice bars, pre-packaged sliced bananas and banana flour.

Already 100,000 tonnes of rejected fruit a year are fed to cows or used to fertilise banana plantations. There have also been trials to convert substandard bananas into bio-fuel.

Woolworths, Australia's largest supermarket chain, requires that its bananas be "slightly arched" in shape, "with blunted butt end and intact, undamaged necks". No "sausage shapes" are permitted; the fruit must measure 160-220mm across the curvature; and it must be "firm [but] not soft", with a "normal-bright bloom" and "nil foreign smells or tastes".

The supermarkets say they are merely reflecting consumer demand, with most people choosing the best-looking fruit.

A Woolworths spokesman, Benedict Brook, told the Sydney Morning Herald: "The fact is that customers, given the choice between fruit that is bruised and fruit that looks pristine, will choose [the latter]."

Similarly stringent standards are set by the rival supermarket chain Coles. The two companies buy 70 per cent of Australia's bananas, the majority of which are grown in north Queensland.

Tony Heidrich, chief executive of the Australian Banana Growers' Council, said customers could help minimise waste. "Perhaps it's more about educating consumers that bananas aren't manufactured in a factory, they're subject to the whims of Mother Nature," he said.

Research suggests a growing demand for smaller bananas, to fit into lunchboxes. Woolworths is experimenting with packs of "lunchbox bananas" in some stores.