The team led by Hirotoshi Utsunomiya, associate professor of Pathology at the university, found the substance through laboratory tests in which they added extracts from umeboshi pickled plums to cells infected with the H1N1 virus.
They found that when the substance is added to the infected cells, the growth of the virus in them was suppressed by roughly 90 per cent after about seven hours, according to the university.
"We can expect to suppress the virus growth by having about five pieces of umeboshi a day," Utsunomiya said, adding that he hopes the findings will encourage people to take a fresh look at traditional Japanese meals.
Umeboshi pickles are often eaten with steamed rice and rice balls containing the pickles are popular at stores in Japan.
The university had been conducting studies since 2006 with funds from five plum processing firms in the town of Minabe and the city of Tanabe in Wakayama Prefecture, a region known for its high-quality plums.