A chef in Taiwan apologises for using lard from Cheng I Food.

Prosecutors said the arrests were all connected to subsidiaries and suppliers of the Ting Hsin food group.

A spokesman for the Ministry of Justice said company suppliers were alleged to have added oil meant for animal feed to its cooking oil products.

Some of the low-quality oil had been bought in Vietnam for over two years.

Consumer groups in Taiwan have called for a boycott of all Ting Hsin's products amid increasing public anger over food safety scandals on the island.

In a national security meeting last night, Taiwanese President Ma Ying-jeou ordered the formation of a cross-department office to deal with food safety. He also called for cooperation between the government and the public to track down firms producing contaminated food.

The allegations surrounding Ting Hsin come after officials from another cooking oil producer, Chang Guann, were formally charged with using recycled food waste in its food products. Health minister Chiu Wen-ta resigned two weeks ago over the food scandals.

Among the people detained in the latest arrests was Tsai Cheng-chou, vice-president of Yung Cheng Oil, who allegedly sold animal feed oil to a Taiwanese subsidiary of Ting Hsin.

"The latest arrest brought to eight the number of suspects we have detained in connection with the scandal," a Ministry of Justice spokesman said.

The others were arrested over the past three days, including Shang Mei-feng, a former general manager of another Taiwanese subsidiary of Ting Hsin.

Prosecutors said they were also investigating if Wei Ying-chung, one of the four brothers who own Ting Hsin, was aware of the fraud. He said he had no knowledge that contaminated oil was used in its products, but last week he resigned from various positions at the company. Consumer and civic groups, backed by more than a dozen city and county governments, hundreds of schools and a number of supermarkets in Taiwan, have boycotted more than 30 products linked to Ting Hsin.

Banks in Taiwan have also said they will reconsider lending to the company.

Food market expert Wang Kuo-an said the boycott was unlikely to do lasting damage to Ting Hsin.

He said the company had a huge business on the mainland and a strong reputation among customers there. "There might be a short-term effect, but not for long," Wang said.