Food watchdogs have found 15 meat samples containing the banned preservative sulfur dioxide, which traders use in order to make meat look fresher. The samples were among 321 the Centre for Food Safety collected across the city between July and last month. Sulfur dioxide at concentrations of between 23 parts per million and 3,300 parts per million were found in 11 beef samples, three pork samples and one mutton sample. Adding preservatives to meat, whether fresh or frozen, is illegal. A spokesman for the centre said normal consumption of meat containing sulfur dioxide at the levels detected should not be harmful to health. 'Sulfur dioxide is water-soluble, so most of it can be removed through washing and cooking. 'But people who are allergic to this preservative may experience respiratory discomfort, headaches and nausea,' the spokesman said. The centre has taken follow-up action, including collecting more samples and issuing warning letters to the shop operators concerned. They would be prosecuted if evidence of wrongdoing was sufficient, the spokesman said. If convicted, traders could be fined up to HK$50,000 and jailed for up to six months. The centre appealed to the food trade not to use preservatives in fresh or frozen meat and to comply with laws. It also reminded people to buy meat from reliable stalls. The centre said sulfur dioxide was not highly poisonous and was commonly used by food manufacturers as a preservative for a variety of foods, including preserved fruit and fruit juice.