The T.K.K. Ruei-guang and Kuen-yang outposts logged acid numbers of 4.21 and 3.13 respectively, well over the accepted norm of 2.0 mg KOH/g, added the media.

Stores were given a grace period of seven days to make improvements or they would be fined anywhere between NT$60,000 and NT$300,000, said the health department. Since the first inspections that took place on June 26, Taipei City health authorities have yet to fine a vendor.

They have audited 553 restaurants thus far, said media.

Lin Jin-fu, a spokesperson for the Taipei's health department, said that all of the nine samples that did not pass the litmus test have been sent to the Bureau of Food and Drug Analysis under the Cabinet-level Department of Health for further testing of toxic heavy metals.

In response to the disclosure of their use of spoiled oil, a public relations representative for T.K.K. stressed that the company would step up efforts in monitoring daily changes of oil at its 40 branches across the island.

T.K.K. had already implemented more stringent protocol after the first random inspections led by government officials and the slip-ups from yesterday were the result of negligence by store managers, said the rep.

T.K.K. was established in 1974 as the first instant food store chain in Taiwan, 10 years earlier than the inauguration of McDonald's first store in Taipei in 1984.

T.K.K. enjoyed its heyday 20 years ago, when as many as 78 chain stores were spread islandwide with a total annual revenue of over NT$500 million. For the moment, the local instant food chain has only 43 stores due mainly to the impact of the global financial tsunami.