Kobayashi Pharmaceutical says it holds samples taken during the manufacturing process of its "beni-koji" materials. The samples are expected to help determine in which stage the materials were mixed with an unintended substance.

A number of people developed kidney diseases and other illnesses after taking Kobayashi Pharmaceutical's supplements that contain "beni-koji" ingredients made from red yeast fermented rice.

The drugmaker stores samples of the "beni-koji" materials produced at its factory in Osaka for each lot. It says an unintended substance, believed to be puberulic acid, was discovered in samples from 10 of the 88 lots produced last year.

The substance may have been mixed into the "beni-koji" materials in the production process. But at which stage that occurred remains unclear.

The firm says the production process is largely divided into "culturing" and "mixing" stages. It also says it stores samples in the culturing stage.

The health ministry and Osaka City have inspected the factory and are questioning company officials to put together a clear picture of the matter.