THE American Army has discovered why fruit keeps better in hot weather when stored in a tin lunch box rather than a plastic container.
Army cooks told the American Chemical Society meeting in San Francisco how they had encountered major catering problems during the 1991 Gulf War when fruit turned brown and developed "armpit" odours.
The forces had switched from unlined tin cans to lighter plastic in 1986.
"During Operation Desert Storm we had loads of apple sauce go all to hell," said William Porter, a food chemist at the Army Soldier Systems Command in Natick, Massachussetts.
By examining a batch of preserved pears, Dr Porter found that vitamin C, added to the fruit as a preservative, was causing the foul smell and browning.
At normal temperatures, the vitamin inhibited fruit-rotting enzymes, but at high temperatures it combined with amino acids in the fruit to form aldehydes - the chemicals causing the smell.
A chemical reaction between tin and vitamin C reduced the vitamin, the researchers discovered.
The tin also combined with chlorogenic acid, found in most fruit, to create a molecule that absorbs ultraviolet light then re-emits it as visible light, so that fruit kept in tin cans appears brighter and more appetising, according to a report in New Scientist.
The Army researchers now advise that fruit should first be stored in cans, to absorb some tin, then transferred to plastic containers.
