
The company said it temporarily closed the outlet in Osaka this week, and sent a notice to 95 other restaurants that offer the kind of green tea latte frappe sold to the woman, who said she sustained injuries to her mouth.
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Dozens of pieces of plastic were found inside the beverage, a company spokesperson told AFP, adding that a plastic instrument used to make the drink may have been the source.
"At this point it is just a hypothesis but we think this plastic tool slipped into a blender to make the frappe," he added.
McDonald's Japan unit has been battered by a series of scandals including a human tooth found in some fries.
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Last summer, a Chinese supplier was found to be mixing out-of-date meat with fresh produce, sending sales plunging and forcing a rapid switch to a Thai vendor.
In April, the company announced it would renovate 2,000 of its 3,000 Japanese outlets and shut down another 130, while reducing its headcount in a bid to cut costs.
That came after it said in February it had lost a worse-than-expected 21.8 billion yen ($182 million) for 2014 -- against a year-earlier profit -- recording its first loss in 11 years.
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