Four out of 167 meat samples were found to contain sulphur dioxide, a banned preservative for meat, according to a report made public Thursday by the Center for Food Safety of Hong Kong.

Samples of beef, pork and mutton were collected at local fresh provision shops and market stalls in February and March for a targeted surveillance project.

The sulphur dioxide found in the four fresh meat samples, including three fresh beef and one fresh pork, were at levels ranging from 22 parts per million ppm to 470 parts per million ppm, according to the center's report, saying the overall satisfactory rate was 97.6 percent.

The results of the three fresh beef samples had been announced in the Food Safety Reports for February and March.

The center has taken follow-up action, including collecting follow-up samples and issuing warning letters to the shop operators concerned.

Following repeated detections of sulphur dioxide in fresh meat samples in recent years, the center continued to conduct the targeted surveillance project this year to assess of the use of the preservative, a spokesman for the center said.

"Individual meat traders have been found using sulphur dioxide to make the meat look fresher," He said.

Under the city's Preservatives in Food Regulation, it is an offence to sell fresh, chilled or frozen meat containing sulphur dioxide, and the maximum penalty is a fine of 50,000 HK dollars ( about 6,435 U.S. dollars) and six months' imprisonment.