Two Hong Kong firms are under investigation for supplying industrial lard oil to the Taiwanese company at the heart of the gutter oil scandal.
It emerged yesterday that trading company Globalway bought lard oil from the Po Yuen Lard Company in Yuen Long, and then sold it to Taiwanese firm Chang Guann.
Chang Guann is accused of blending it with gutter oil - which is an illegal substance made by recycling kitchen waste.
In Hong Kong, fast-food chain Café de Coral was found to have used a batch of lard oil made by Chang Guann between March 18 and April 8 this year to make "Western-style" sauce. None of the oil remains.
A spokesman said the company "had no knowledge" of the source of the lard oil. Their local supplier said the oil had passed quality tests before being sent to the food chain.
Bakery chain Maxim's Cakes removed pineapple buns from their shelves over the weekend. They said there was no evidence that the oil used to make the buns was tainted, but they were removing the buns "to be ultra-cautious on food safety".
Po Yuen's owner has responded by saying his company's products are not to be eaten.
"Our products are for industrial use," the owner, giving his name only as Kwok, told Cable TV. "The Food and Environmental Hygiene Department requires us to state that our products can't be used for human consumption.
"None of our lard oil products are to be eaten."
Dr Ho Yuk-yin, a consultant at the Centre for Food Safety, said officers were investigating where Po Yuen got its oil from. Taiwan's Food and Drug Administration (FDA) said Chang Guann had imported 87 tonnes of oil from Hong Kong this year.
In Hong Kong, food authorities tried to calm the public over the deepening food scare.
"According to the latest information provided by the relevant authorities in Taiwan, they so far have not identified any sub-standard lard being exported to Hong Kong," Ho said.
Taiwan's FDA said certain samples of oil supplied to Chang Guann contained more than triple the acceptable level of carcinogenic benzo(a)pyrene, and exceeded acceptable acid value levels, too.
However, lab tests revealed that the Chuan Tung brand of lard produced by Chang Guann had been refined and met all safety requirements, except for a heavy metal test which had yet to be completed.
But Harold Corke, an expert in food science at the University of Hong Kong, said gutter oil could contain many different kinds of harmful chemicals, and it was difficult to test for them all.
"The tests alone cannot indicate the gutter oil is safe for consumption," he said.
"The suppliers scoop up whatever they can get. There could be industrial materials in the gutter one day and pesticides another.
"You can't test for everything everyday. And you wouldn't want to eat [food made with gutter oil] anyway because it is produced with the wrong material in [the] wrong way."
Check out the graphic below which shows how the gutter oil was made and what dangerous chemicals it may have contained.