Dairy products from Westland Milk sent to China have been quarantined after concerns were raised about nitrate levels.
Hokitika-based dairy cooperative Westland Milk Products said a small amount of lactoferrin powder with elevated nitrate levels had been exported to China.
The product - which is a protein - had been traced and quarantined, Westland said.
The nitrate levels did not comprise a food safety risk, it said in a statement.
Chief executive Rod Quin said Westland had reported to the Ministry for Primary Industries (MPI) that two batches of lactoferrin, totalling 390kg, showed nitrate levels of 610 and 2198 parts per million respectively.
Quin said that, based on investigations to date, it appeared to be an isolated incident in the lactoferrin plant only where traces of cleaning products - which contain nitrates - were not adequately flushed from the plant prior to a new run of product. The New Zealand maximum limit for nitrates is 150 parts per million.
MPI said it had revoked export certificates for four consignments of lactoferrin made by Westland following the detection incresaed nitrate levels.
One batch was exported directly to China as an ingredient for other dairy products by Westland, and the second batch was supplied to Tatua Co-operative Dairy Co, and also exported to China, MPI said.
"Almost all of these products are now confirmed as detained in the supply chain," MPI said. There was no affected lactoferrin used in products in New Zealand, the ministry said.
"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," MPI acting director-general Scott Gallacher said.
"MPI, the Ministry of Foreign Affairs and Trade and the companies concerned are working closely with the Chinese authorities on this issue," MPI acting director-general Scott Gallacher said.
The announcement from Westland follows news early this month that China had temporarily suspended imports of whey powder from Fonterra after three batches were found to contain Clostridium, which is part of a family of organisms which can cause bacteria, some of which are linked to food poisoning.
Westland - the New Zealand's second biggest dairy cooperative after Fonterra - said the product was initially not identified as non-compliant during Westland's routine testing regime prior to export. All of the 390kg of non-complying lactoferrin was sent to China.
Food safety was not the issue because lactoferrin is used as a very minor ingredient in food products. "This means that, even if the lactoferrin with elevated nitrates had been added to food, the retail products would still have nitrate levels significantly below allowed limits," Quin said.
Westland also put a hold on all of its lactoferrin in its own warehouse and commenced re-testing all individual batches. All other lactoferrin product tested to date has returned results well below the New Zealand nitrates limit. No other Westland products were affected, he said.