More than 21 tons of illegal lard made from waste pig parts has been sold to college dining halls and local markets in the last two months in Changsha, capital of Central China's Hunan province.

And since 2007, more than 200 tons of lard with sales of 1.4 million yuan (US$205,000) have been produced by an underground workshop in the Yuhua district in Changsha, which was busted at the end of April, Xinhua News Agency reported on Sunday.

"Scattered around a shabby shed in a remote area of the city were filth, odds and ends, and all sorts of pig waste. The stink attracted swarms of flies. Beside two huge black boilers were several large buckets, all filled with newly made lard," the report said.

"No one would ever want to eat any lard after seeing the scene," an unnamed official who participated in the raid was quoted as saying.

The workshop had no license or certificates, said Li Xiaoqun, deputy director of the Yuhua branch of the Changsha Administration of Industry and Commerce.

Four account books found by officials noted sales of the lard - and college dining halls appeared to be the biggest consumers.

From Feb 23 to April 26, more than 21 tons of such lard were sold to dining halls, construction sites, restaurants and oil shops. About 30 percent of it was sold to college dining halls.

The owner of the workshop, surnamed Zhou, said he had been doing business with the Hunan International Economics University dining halls for over two months.

On the university website, an apology letter dated April 30 was addressed to students, teachers and staff.

"Investigations found illegal lard used in dining halls. Relevant dining operators will be transferred to quality authorities for further investigation," the letter said.

Zhou was put in criminal detention on Saturday, police said.

However, sample tests on the lard provided by the Changsha bureau of quality and technical supervision showed the product had passed quality inspections.

"If so, it means the lard is technically 'qualified food product,' and Zhou would only be suspected of illegally operating the business," the report said.

It quoted an unnamed expert involved in the case as saying that the current national food hygiene inspections were of "low standards, narrow coverage and outdated technologies."

Most of the standards were established when food shortages still existed in the country, but they have failed to keep up with recent developments, the expert said.

Many illegal manufacturers even modify their methods based on the standards so their products can pass quality inspections, the expert was quoted as saying.

In its Monday editorial, the Beijing News cited inefficiency from the regulatory departments as a reason for lagging food safety standards.

"In some foreign countries, food safety authorities usually manage the standards actively, meaning regular adjustments based on food safety crisis evaluations," the editorial says.

"However in this country, regulatory departments hardly ever evaluate potential food safety crises, and it's pretty normal for food safety standards to remain unchanged for almost a decade."

From April 30 to May 25, the Ministry of Health will collect public advice online. Citizens, legal parties and other organizations are encouraged to submit suggestions for national food safety standards.