Bright Dairy & Food Co. Ltd. (600597.SH), a dairy giant in China, has apologized for allowing some of its Ubest brand milk to get contaminated by alkaline water, a chemical used to clean equipment.

Due to a problem with an automatic valve, some food-grade lye leaked into a production line around 5 pm Monday, which was destined for the 950 milliliter packages of its Ubest brand of milk, according to a news release issued on the company's website.About 300 of cartons of Ubest, which had hit the market Tuesday, were affected, the announcement said.

According to the Shanghai Quality and Technical Supervision Bureau, Bright is recalling hundreds of the products and has contacted the customers who bought the tainted milk

The bureau is still investigating the case and demanded Bright give a clear report about the mishap, including the recall result, customer complaints and the food safety hazard, Shanghai Daily said.

Meanwhile, the bureau has taken samples of some Ubest milk produced on Monday for testing. It also reminded citizens not to drink the 950ml Ubest fresh milk produced on Monday.

A netizen said she mixed purple sweet potato into two cartons of Ubest fresh milk produced on different dates and found one carton turned purple and the other blue. She also posted the picture of them on Weibo.com, China’s biggest microblogging website.

The post circulated quickly and was reposted more than 7,000 times by the time of writing.

Because the food safety issue is of concern to the public, the national media immediately put a strong focus on Bright Dairy.

Earlier this month, China’s prominent dairy company, Inner Mongolia Yili Industrial Group Co. Ltd. (600887.SH) recalled one brand of infant formula after government tests found mercury traces.

Meanwhile, global food and dairy companies are making another round of big bets on China's fast growing dairy sector, AFP said. They are lured by projections of 10 percent annual growth for the sector and by Chinese consumers' willingness to pay a premium for foreign brands as they remain wary of local brands' safety records.

For instance, Denmark’s dairy giant Arla Foods became a strategic investor in Mengniu Dairy Co. Ltd. (2319.HK), China’s largest milk producer by sales volume, after buying a 5.9 percent stake at a price of 1.7 billion Danish crowns ($289 million) recently.