NHK has obtained a photo of blue mold found at a Kobayashi Pharmaceutical plant that produced ingredients for supplements linked to numerous health complaints.
The mold is said to be of the same type as the one that generates puberulic acid, which has been detected in products that caused kidney problems among users.
The blue mold in the photo was collected from the company's Osaka plant during inspections by the city in western Japan. The plant had produced "beni-koji" red yeast fermented rice ingredients until last December.
The photo shows the mold after it was cultured for several days.
Sources close to Osaka City say inspectors found moldy black spots inside the plant when they visited the facility in late March. That was soon after the health issues came to light.
The sources say inspectors returned to the plant in April, and detected mold from samples taken from walls, ceilings and other places in five rooms, including one for fermentation.
Yaguchi Takashi, an associate professor at Chiba University's Medical Mycology Research Center, says the blue mold found at the plant is a relatively rare type that has not been studied in-depth and is different from those commonly found in food factories.
He added the mold may have existed in the outdoor environment near the plant, before it entered and spread inside.
Most of the rooms at the plant are said to have been sealed off by walls and doors.
Osaka city officials plan to investigate when and how the blue mold spread within the facility.