The president of Japan's biggest dairy firm Snow Brand Products has quit after the country's worst outbreak of food poisoning for 30 years.More than 12,000 people fell ill from drinking contaminated low-fat milk and local authorities ordered the company to shut its Osaka plant in western Japan at the weekend. Local authorities ordered the shutdown after discovering there was no proper maintenance record for one of the milk storage tanks and the cause of the outbreak was traced to bacteria in a valve in the milk production line, which had not been cleaned properly.The company also stopped part of its operation at its Hino plant in Tokyo on Thursday.Snow Brand President Tetsuro Ishikawa said he would resign at the end of September."I think is would be the best for me to apologise and step down," Ishikawa told a press conference.He continued to say: "We had been confident about security control due to our long business experience. From now on we will listen to outside opinions to transform ourselves into a new company."Reports said 12,027 people have so far fallen ill, about 160 people have needed hospital treatment and 30 are still being detained in hospital.The outbreak has already caused a sharp drop in Snow Brand's share price and reports said shares touched 396 yen on Thursday, down 30.5% since 30 June.