The technology, which sterilises and extends the shelf life of foods without cooking or damaging it, was developed by a private company founded by professors at Texas Tech University in Lubbock.

The researchers say their work is aimed at reducing outbreaks of illness. They are still awaiting patent approvals for the technology, but a group of journalists was given a tour of the basement laboratory where it was developed.

Some 48 million Americans become ill every year from contaminated food, according to the Centres for Disease Control and Prevention, with outbreaks this year linked to tainted melons, mangoes, meat and peanut butter.

The company, called MicroZap, is also promoting the technology as a solution to the superbug MRSA, the dangerous drug-resistant infection that is now endemic in many US hospitals.

As well as the bread, researchers have successfully treated pet food - which was responsible for the majority of recalls this year - fresh turkeys, leafy herbs such as coriander, and jalapeno peppers.

''We tried a slice of bread and then checked the mould after 60 days and it had the same level of mould that it did when it came straight out of the oven,'' Don Stull, the chief executive of MicroZap, said.

''What we are trying to do is give some ability to have a long shelf life without the preservatives.'' The technology uses pulsed microwave frequencies from multiple sources to pasteurise food. The food is zapped for a set time - 40 seconds for jalapeno peppers, for example. Unlike conventional microwave ovens, there are no hot and cold spots, and the process does not damage or cook the food, Mr Stull said.

The company claims its technology is more effective at killing salmonella and E. coli than existing methods. It will also be more palatable for the public than irradiating food, Mr Stull said.

He acknowledged the everlasting loaves may not necessarily be of interest to the average consumer.

''You probably won't see a lot of people wanting 60-day old bread,'' he said.