China Mengniu Dairy Co, the country's largest dairy company has found excessive levels of a cancer-causing toxin in its milk, the latest in a series of tainted milk scandals that have hit China in recent years.

Mengniu Dairy was among the 22 other dailies in China involved in the melamine-contaminated infant milk scandal in 2008 that forced the head of China's quality department to resign (See: China's quality chief resigns over toxic baby-milk scandal).

The government's quality watchdog, the General Administration of Quality Supervision Inspection and Quarantine (AQSIQ), on Saturday said that it conducted a random check of 200 dairy products in 21 provinces, and found two products, including one manufactured by Mengniu, to contain excessive aflatoxin - a substance that can cause liver cancer.

The Inner Mongolia-based dairy producer said on Sunday that the milk, produced at one of its plants in Meishan, in the southwestern province of Sichuan, was tested by AQSIQ testers before being sold and destroyed before reaching the market.

"Mengniu would like to express our sincere apologies to consumers," the company said in a statement, adding, "We will draw a big lesson from this incident and will work harder to meet all national and corporate standards on quality in the future,"

According to the test result published on the general administration website, government testers found 1.2 micrograms of the toxic substance in a 250-ml pack of pure milk produced by Mengniu on 18 December, while the national standard allowed a maximum of 0.5 micrograms carcinogenic content in a kg of milk.

The Chinese Daily, quoting Fan Zhihong, associate professor with China Agricultural University's college of food science and nutrition engineering, said, ''Carcinogen can accumulate in the human body, and is resistant to heat. It dissolves when the temperature reaches nearly 300 C, which means high temperature disinfection or pasteurising (a common disinfection method used in the dairy industry) cannot kill it at all."

Dairy experts say that the problem might be traced to cattle feed being contaminated by aflatoxin. "Cattle feed, such as corn, rice and soybean, will produce the poison after having been stored for a long time," the paper said, citing remarks made by Wang Dingmian, chairman of the Guangzhou Dairy Association.

The latest scare comes after China was hit with a series of food safety scandals starting from 2008, when industrial chemical melamine was illegally added by some dairy companies and local milk suppliers to dairy products to give misleadingly high readings for protein levels.

The melamine scandal caused the deaths of six infants and 300,000 others to fall ill. This incident came four years after at least 13 Chinese babies died of malnutrition after their parents unwittingly fed them fake baby formula that lacked nutritional value.

Mengniu was among the 22 other companies that were at the centre of the melamine scandal along with rivals Sanlu Group and Yili Industrial Group.

Mengniu was again involved in two incidents in 2010 and April this year that saw more than 200 children being hospitalised after consuming the company's milk at school.