A total of 53 officials who were partly responsible for several recent scandals involving the sale of melamine-tainted milk have been punished as China steps up its efforts to ensure food safety.

Xinhua News Agency reported on Monday that 17 of them were dismissed and others faced various penalties, ranging from demotions to demerits and warnings.

The move followed the sentencing of 14 people convicted of producing or selling tainted milk powder in Shanxi and Hebei provinces on Friday.

Among the 14 involved in the four recent cases, two were sent to prison for life, four received sentences of 10 to 15 years and the rest received lighter sentences.

Three years after the use of melamine in infant formula killed at least six babies and prompted a shake-up of China's dairy industry, the authorities are still seizing tons of tainted milk each year. Farmers or processors add melamine to watered-down milk to ensure it appears to have high levels of protein.

One of those sentenced to life in prison by the Intermediate People's Court in Shanxi's Jinzhong city, was a producer named Li Baosheng, who had sold 130 tons of milk powder containing melamine, Xinhua said.

The other who received a life sentence was identified as Qi Weigang, who was convicted of selling Li 11.3 tons of tainted milk powder.

Zhao Chunfeng, general manager of the Yuquan Dairy Co in Chengde, a city in Hebei, was sentenced to 15 years for selling tainted milk that had been recalled and producing substandard milk powder, Xinhua said.

In 2008, nearly 300,000 children were sickened and six died after consuming infant formula that contained melamine, which can cause kidney damage. Dozens of people were arrested and a dairy farmer and a milk salesman were executed.

New cases of phony or tainted food or medicine are reported regularly, despite crackdowns and threats of severe penalties.

So far this year, the authorities have uncovered the sale of drug-tainted pork, bean sprouts treated with a carcinogenic chemicals and stale bread treated with sweeteners and dye to make it seem fresh.

About 26 tons of melamine-tainted milk powder was seized from an ice cream maker in the southwestern municipality of Chongqing, local police said last Tuesday.

The spate of problems prompted the State Council, or China's Cabinet, to order a renewed crackdown against illegal food additives.

On Saturday, President Hu Jintao said inspection efforts must be raised to ensure the safety of food. He made the comment during a visit to Tianjin Product Quality Inspection Technology Research Institute.