The US agribusiness giant Archer Daniels Midland has been forced to confront a history of alleged price-fixing and market-rigging as its seeks to win regulatory approval for its controversial takeover of GrainCorp

ADM has encountered intense questioning from a Senate estimates committee amid concerns that the $3 billion deal would put a foreign stranglehold on grain storage and infrastructure.

The company's grains boss Ian Pinner attempted to deflect the past accusations during occasionally hostile questioning, and has assured the committee that ADM is now a fundamentally different business.

Mr Pinner is in Australia to convince farmers and the Foreign Investment Review Board that the GrainCorp takeover will not leave them worse off.

He also has to win over politicians like Liberal senator Bill Heffernan, who has been digging into ADM's alleged history of price-rigging and corruption.

Senator Heffernan, himself a GrainCorp client, confronted Mr Pinner with a myriad of past accusations and proven incidents that go to concerns about ADM's ethics and market power.

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"It's less than glorious, your past record," the Senator said to Mr Pinner during the hearing, before reading out a number of headlines from media reports.

"Archer Daniel Midland settles price fixing charges for $400 million; Deal in food enhancer fixing suite on hold; Court reinstates seed alleging Archer Daniels suite in the market rigged; Archer Daniels accused of espionage; Big citrus acid buyers sue Archer Daniels; Former ADM official indicted for fraud; and so it goes on."

Mr Pinner told Senator Heffernan that those episodes would not be repeated.

"Senator, there have been incidents in the past which ADM is not proud of, that is absolutely clear, but I would say that there have also been changes," he said.

"ADM is committed to not only acting in a compliant way but acting in an ethical way."

The Senator offered a warning.

"Can I just tell you that our mob here, GrainCorp, we're not into that s***," he said.

"No. And we don't want anything to do with anyone that is."

The New South Wales Nationals Senator Fiona Nash also appeared unconvinced, despite ADM's assurances that it was all history.

"Is price fixing a mistake? How do you term that as a mistake?" she asked.

"I think you're referring to an incident which was nearly 20 years ago now," Mr Pinner replied.

"Sorry, no. The timeline's not of that much interest, we're actually trying to get a sense of the company, where it's been, where it is now, in terms of fit and proper," Senator Nash said.

ADM is also trying to hose down concerns that grain grower access to storage and transport infrastructure that comes with the deal.

ADM says its committed to fair and open dealing, and plans to ramp up its infrastructure spending to $300 million.

But once again Senator Heffernan suggested the deal would hurt rather than assist farmers.

He also wanted assurances that A-D-M was committed to paying its fair share of Australian tax if the deal goes through, given recent allegations that giants like Apple and Google have been avoiding it.

"We hope we don't put the hurdles too high for you but we, also in your aspiration, we want to include a national interests benefit and make sure you pay your tax and all the rest of it," he said.

"God bless you and get on that plane and have a safe journey."

"We will pay our tax, chairman, we can assure you of that," Mr Pinner replied.

The Senate grilling was a warm-up for what might be in store for ADM as it works to convince the Foreign Investment Review board that the GrainCorp takeover passes the national interest test.

The Treasurer Wayne Swan gets the final say.

But unless there is a decision by the 12th of August when the government goes into caretaker mode, a potential Coalition Treasurer could be influenced by National Party concerns.

You can follow Peter Ryan on Twitter @Peter_F_Ryan or on his blog.