The suspect used ethylene glycol, a chemical in antifreeze and brake fluids, which can be fatal in large quantities.
Local deputy chief of police Uwe Stuermer described the man as "eccentric" and mentally disturbed.
The man was detained by officers near Tubingen, south of Stuttgart, following information received from the public, police and prosecutors said in a joint statement.
A German man is charged with threatening to disperse poisoned baby food throughout stores in Europe if the companies didn't fork over $11.8 million in blackmail money.
On Thursday, officials launched an urgent appeal and published CCTV images of the suspect - sparking hundreds of calls from the public.
The blackmailer alerted authorities that five jars of baby food at shops in Friedrichshafen, near Konstanz, had been tampered with.
The man appeared to be in his fifties, of average height, and was wearing glasses and a hat. The suspect's name was withheld under German privacy laws.
They said that while there was no need to panic, shoppers should remain vigilant.
Through the video surveillance of the stores where the baby jars were identified, police were able to obtain images clearly showing the face of the 55-year-old man, who has not been named.
Earlier this month, police received an emailed threat to distribute 20 types of poisoned foodstuffs into supermarkets across Germany and overseas if they did not pay a sum believed to top €10 million ($12 million). Prosecutors are deciding whether to charge him with attempted murder, which could entail a life sentence.
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