BEIJING - Many customers want McDonald's Corp to release more information on so-called "pink slime", after the company officially denied the use in its hamburger products in China, but McDonald's said on Sunday it had no plans to make further comment on the issue.

The ammonia-treated beef, or the selected lean beef trimmings as the company calls it, hasn't been used in meals since last year.

"This product has been out of our supply chain since August of last year," McDonald's said in a statement.

"We are always reviewing and evolving our standards to ensure we continue to serve safe, high-quality food to our customers."

The use of ammonia-treated beef has been approved by the US Department of Agriculture, meaning that it is generally recognized as safe.

"In China, the use of it as a production procedure is also acceptable under the relevant laws," said Fan Zhihong, an assistant professor at China Agricultural University's college of food science and nutritional engineering.

"But with the addition of certain acids, ammonium hydroxide can turn into ammonium nitrate. More important, 'pink slime' is usually used as animal food in some countries. That could cause some people to feel disgusted when consuming such beef."

McDonald's China, the management authority for the third-largest market of the world's leading fast food chain, issued a public announcement about the substance, saying: "The quality and safety of food for our customers is a top priority. Beef in the hamburgers is all fresh, which means no ammonium hydroxide."

However, an online survey conducted by Sina, a popular website, found wide skepticism about the announcement.

More than 88 percent of the 24,980 respondents as of 6 pm on Sunday said they didn't believe that the branches in China had not used the substance.

About 70 percent of the respondents said they would not buy such products anymore.

"They are proud of their uniform standards for raw material supplies around the world. How could it be that the US stores were using 'pink slime' while those in China weren't?" asked Zhang Yanchen, a resident from Shijiazhuang, Hebei province.

Many other comments also asked the company to give more information.

"Double standards on food quality are never allowed in the world," said Qiu Baochang, head of the lawyers' group of the China Consumers' Association. "Customers have a right to know. Besides, as a responsible company, it should act to retain its reputation."

An official from the public relations office of McDonald's China, who would only give her surname as Weng, said the company had released the necessary information and no further statements would be issued for now.

However, many customers are still eating happily at McDonald's. A branch on Heping West Street in the Chaoyang district of Beijing was well-patronized at lunchtime on Sunday.

Seven of the customers said the "pink slime" issue did not bother them, as they do not eat the hamburgers. Three had not even heard about the issue.

"The news about the ammonium-treated beef didn't have a negative influence on customer volume during the weekends," said Zhang Peng, the manager of the branch.

"I have faith in McDonald's. I once visited the company, which left me deeply impressed with its strict supervision of supply and other procedures," said Dong Jinshi, executive vice-president of the International Food Packaging Association.

He said that the company should allow more consumers to trust its products by giving a prompt response to requests and organizing people - including customers, experts and government officials - to visit their production facilities and see for themselves.