Mrs Kroc's fortune came from burgers and fries

Joan Kroc's gift is thought to be the biggest ever given to a single charitable organisation.

Mrs Kroc left the money on condition that the Salvation Army uses her burger bar fortune to build community sports centres for working class children.

She has asked the Salvation Army to build more than 25 centres in the US.

'Born again'

Mrs Kroc died of a brain tumour in October 2003 in California.

"This is a new era for the Salvation Army in the United States," the evangelical Christian group said on its website.

Its US national commander has described the gift as "a real shock".

"You sit down when you learn something like that," Commissioner W Todd Bassett was quoted as saying by the Financial Times newspaper.

Mrs Kroc's community centres will be similar to an existing one in San Diego - also funded by her - which has swimming pools, an ice rink, gymnasium and sports fields, the Salvation Army said.

The Indiana University's Centre for Philanthropic Giving, which tracks donations over $1m, believes it is the biggest gift to a single organisation, the Los Angeles Times reported.

Microsoft founder Bill Gates has given more money at one go - $6bn - but it was spread across many causes.

Golden years project

Ray Kroc was already in his mid-fifties when he founded McDonalds Corporation, now the world's biggest restaurant chain, in 1955.

He was selling milk-shake machines when he was impressed enough by a customer's burger bar to buy it.

The Krocs were self-made billionaires; Mrs Kroc's father was a railway worker and her husband - who died in 1984 - once topped up his salary by playing the piano in a radio station at night.

McDonalds, the source of their fortune, is now an American icon. But it has suffered lean times recently, being forced to restructure after posting a fourth quarter 2002 net loss of $343.8m.

Mrs Kroc also left another $285m in other donations.