Police have detained five people as part of their investigation.
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Shanghai Municipal Food and Drug Administration has found that Shanghai Husi forged the production dates on smoked beef patties produced in May 2013 and sold them as being made in January 2014, Xinhua said. The processed meat had a shelf life of nine months, it added.
Xinhua said there were 4,396 batches with forged dates, of which 3,030 had been sold.
Officials at Shanghai Husi and OSI in China could not be reached for comment. OSI has apologized to its Chinese consumers, calling what happened at the Shanghai plant "completely unacceptable".
The scandal, which has dragged in global food chains including McDonald's Corp, KFC-parent Yum Brands Inc and Starbucks Corp, was prompted by a local TV report on Sunday which showed staff at Shanghai Husi using long-expired meat and picking up food from the floor to add back to the mix. It also alleged the firm of forging production dates.
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Reuters reported on Friday that Shanghai Husi won a court case earlier this year against a former quality control officer whose claims included that he was made to forge meat production dates.
The former worker told a court last year he was unwilling to illegally forge dates at the plant, adding that he repeatedly urged his employer to change a practice which he said violated food safety laws and hurt consumer interests, according to court documents seen by Reuters. He said Shanghai Husi ignored his pleas. The judge dismissed the allegation due to lack of evidence.
So far, there have been no reports of consumers falling sick in the latest food scare.
Food safety is one of the top issues for Chinese consumers after a scandal in 2008 where dairy products tainted with the industrial chemical melamine led to the deaths of six infants and made many thousands sick.