Fonterra CEO Theo Spierings has said the world’s largest dairy exporter will increase checks at its infant nutrition plants as the company seeks to reassure the market in the wake of the botulism contamination saga.

Spierings insisted the New Zealand dairy giant would “check, double check, triple check if necessary” through a series of measures to provide what the company called “additional quality assurance”.

He said: “Every year, each of our plants undergoes thorough maintenance and review during winter, before being re-commissioned for the new season. They are also routinely cleaned, tested and maintained throughout the season. This year – in light of the precautionary recall – we are going one step further.”

The announcement came as Fonterra looks to allay concerns over its business after batches of whey protein concentrate were found to contain a bacteria that could cause botulism. The scare prompted product recalls across Asia, bans on imports by Russia and China and criticism of what is New Zealand’s largest company.

The New Zealand government this week launched an inquiry into the affair, while Fonterra is also carrying out two of its own investigations. Two senior managers at Fonterra have been placed on leave. Last week, Gary Romano, the head of the company’s domestic milk products business, quit the business. Fonterra did not specify whether Romano’s resignation was directly linked to the contaminatioon but he is the first senior executive to leave the company since the recall. Spierings has assumed responsbility for Fonterra’s domestic milk operations.

Fonterra’s programme of extra checks and servicing of equipment and processes will start at the company’s Hautapu site next week.

The contamination saga has made national headlines in China, a fast-growing market for infant formula and a key export customer of Fonterra.

In the last 24 hours, it has emerged 42 metric tonnes of Fonterra milk powder bound for China in May was withdrawn after it reportedly contained high nitrate levels. China’s block on the batch came despite positive tests in New Zealand, Fonterra said.

“There are times when test findings differ between country of origin and country of destination. This can be due to a variety of reasons, including changes in product conditions during shipment, and different laboratories and testing methodologies,” Ian Palliser, Fonterra’s director of food safety and quality, said.

“The product was tested before leaving New Zealand and met specifications. It was then shipped to China, where local tests showed it no longer met specifications. The product was immediately put on hold and regulators in both China and New Zealand were informed. The product remained 100 per cent within Fonterra’s control, did not enter the Chinese market, and there was no food safety risk involved.”