The quarantine authorities have announced the suspension of imports of lactoferrin from Westland Milk Products, a dairy producer based in New Zealand, after discovering excessive amounts of nitrate in the lactoferrin supplied by the company.

The incident follows close on the heels of a scandal involving Fonterra, the largest dairy company in New Zealand, which admitted on Aug 5 that 38 metric tons of its whey protein was contaminated with a bacterium that can cause botulism.

In a statement published on Monday, the General Administration of Quality Supervision, Inspection and Quarantine said the Wondersun Dairy Co, which is based in Northeast China's Heilongjiang province, found an excessive amount of nitrate in two batches of lactoferrin imported from Westland.

Yu Ningjiang, deputy manager of Wondersun, confirmed the news to china.com.cn, saying that the company has returned 390 kilograms of lactoferrin it had imported from Westland.

Rod Quin, chief executive of Westland, said in an announcement on Monday that the nitrate levels of the two batches totaling 390 kg were 610 and 2,198 parts per million, while New Zealand's maximum limit for nitrates is 150 parts per million, but the problem was not identified before the product was exported to China.

According to the Chinese standard for infant formula, the amount of nitrate should be no more than 100 milligrams per kilogram of powdered milk.

The two batches affected have been prevented from entering the consumer market, according to the administration.

"The administration has asked that the products be sealed, and decided to temporarily stop importing lactoferrin from Westland," said the administration. "It has also asked all the dairy companies based in New Zealand to provide the test results for nitrate in their lactoferrin exported to China, and the company of Westland to provide such test results for its other products exported to China."

Westland said it has started retesting all its batches of lactoferrin, which it has held up in its warehouse. So far, no batches have been found to exceed the safe level.

"Westland is of the view that it is an isolated incident in the lactoferrin plant only, where traces of cleaning products (which contains nitrates) were not adequately flushed from the plant prior to a new run of product," said Quin.

The Ministry for Primary Industries of New Zealand said on Monday that it has revoked export certificates for four consignments of lactoferrin manufactured by the company, and has sent a team to the Hokitika factory, where the contaminated lactoferrin comes from, to investigate the cause.

"MPI's technical experts have looked closely at this issue and believe any food safety risk to Chinese consumers is negligible because the quantities of lactoferrin used in consumer products was very small, meaning the nitrate levels in those products would easily be within acceptable levels."

China's quarantine administration agreed.

Lactoferrin can be used as an ingredient in a number of dairy products including infant formula, and an excessive amount of nitrate in lactoferrin doesn't necessarily lead to an excessive nitrate amount in the dairy product, said the administration.

However, it said that infant formula makers should test all their ingredients in case ingredients other than lactoferrin were contaminated with nitrate, driving up the level of nitrate in infant formula.