Maeil Dairies Co., a major dairy product manufacturer, on Monday issued an apology over an accident involving the mixing of cleaning solution in one of its sterilized milk products during production.

Maeil Dairies CEO Kim Seon-hee said in a statement posted on the company website that a valve operation error momentarily caused cleaning solution to mix with the 200 milliliter sterilized milk product at the company's manufacturing plant in Gwangju, about 270 kilometers south of Seoul, on Sept. 19.

"We sincerely apologize to our customers who have been shocked by this issue," Kim said.

The company said about 50 units delivered to a single specific client were affected by the incident.

The issue came to light after some employees at a major corporate research center reported symptoms, such as stomach pain and discoloration, after consuming the product provided through the company cafeteria last Thursday. (Yonhap)