The contamination has been blamed for the deaths of four children and kidney ailments among 54,000 others. More than 13,000 children have been hospitalized and 27 people arrested in connection with the tainting.
An additional 31 batches of Chinese milk powder were found tainted with the industrial chemical melamine, according to data seen on the food safety administration's Web site Wednesday. Out of the 20 companies on the list, 15 have not been named in previous tests.
The new batches being tested were mostly milk powder products for adults. A previous round of tests found melamine in 69 infant milk powder batches.
The new figure brings to at least 100 the number of tested batches of milk powder found to contain melamine. Dozens of brands sold by more than a score of dairy firms, including some of China's biggest names, have been among those tested.