Food safety investigators, including two senior scientists, say they have discovered how one of New Zealand's highest-priced dairy exports was being inadvertently contaminated with low levels of melamine.
The contamination of the "bio-active" milk protein lactoferrin made by Morrinsville-based cooperative Tatua - and selling for about $500,000 a tonne - was discovered during in-market testing in China during September.
Testing showed levels up to 4 parts per million (ppm) of melamine - much lower than the 2563 ppm in the Beibei infant formula produced by Fonterra's Sanlu joint venture in China - but sufficient to trigger concerns at the height of the controversy over the poisoning of thousands of children there.
The problems were exacerbated when tests on lactoferrin made by Westland Milk at Hokitika also showed melamine contamination of about 1 ppm.
Both companies used the same ion-exchange manufacturing process, but no melamine was reported in lactoferrin made by Fonterra, which uses a different process.
"This trace level may have arisen out of this specific unique process," Food Safety Authority (NZFSA) director of compliance and investigation Geoff Allen said at the time.
Westland acquired its production system from Tatua Cooperative Dairy Company, which specialises in dairy-based proteins and protein derivatives.
NZFSA had set a 1ppm limit on melamine in infant formula, a 2.5ppm limit on melamine in foods on shop shelves, and a 5ppm limit on foods which might be used as ingredients. Lactoferrin is normally less than 1 percent of the ingredients in infant formula, but the two companies suspended their exports of lactoferrin.
Tatua chief executive Paul McGilvary said that though the NZFSA and major multinational food companies including Nestle and Heinz had argued that low-level melamine contamination did not pose a health risk, the Chinese dairy scandal involving Sanlu had triggered consumer sensitivities around the world.
Consumer perceptions were important even where contamination levels were so low they did not present a health risk, he said.
This proved true when South Korean authorities have found trace amounts of melamine in Tatua lactoferrin and banned all other products made by the company pending further tests.
NZFSA suspected that the contamination probably came from seals or plastics used in equipment used to manufacture lactoferrin, which is concentrated 14,000 times from its levels in raw milk.
Bill Jolly, NZFSA's deputy director for export standards, said today that after many trials and "much sequential testing" by Tatua the source of the melamine was finally isolated to a type of disposable filter used right at the end of the processing.
"Tatua has subsequently re-engineered its process replacing the implicated disposable inline filter system with a new filtration plant," he said.
"Subsequent testing has confirmed no levels of melamine above the limit of detection of the method. Westland has also changed the type of filters it was using and has had similar results".
Since then, exports had resumed.
