Researchers in China, where at least six children died in a tainted milk scandal in 2008, have identified seven stable molecules in cow's milk that they hope to use to create a test to identify tainted dairy products.

Some 300,000 children suffered kidney problems after consuming milk containing melamine, an industrial compound that was added to artificially raise protein levels in tests. At least 50,000 babies were hospitalized, many with kidney stones.

In a paper published in Cell Research on Tuesday, scientists described how they analysed raw milk taken from a farm in eastern China and found it contained naturally occurring molecules or biomarkers, called microRNAs.

"The most important implication from this finding is quality control. We can use these biomarkers ... and develop a test kit for random sampling of milk. Our test can tell if milk has been diluted," said lead researcher Zhang Chenyu at Nanjing University's School of Life Sciences.

Hundreds of such molecules were found but seven were consistently present at all stages of lactation, from colostrum to mature milk, Zhang said by telephone. "We found seven stable microRNAs in cow's milk that were consistent throughout different stages of lactation," he said.

Colostrum is milk produced in late pregnancy containing high levels of antibodies. The scientists said they had analysed milk samples diluted with melamine, egg protein and soybean protein and found sharply reduced levels of the seven molecules.

"These results clearly demonstrate that ... microRNAs can be an ideal biomarker for discriminating substandard or manipulated milk from raw milk," they wrote in the paper.