Shirley Ybarra, 50, of Sunrise was arrested last week at a Publix in Tamarac, The Miami Herald reported.
Security cameras captured Ybarra using rubber gloves to mix a substance into jars of baby food, said Dani Moschella, a spokeswoman for the Broward County Sheriff's Office. The substance, which has not yet been positively identified and is to be sent to the Food and Drug Administration for testing, was described as dark, acrid and smelling of ammonia.
When an employee asked Ybarra what she was doing, she claimed she was mixing up food for her son, Moschella said.
The tainted baby food was in Ybarra's supermarket cart, and investigators said there was no evidence she intended to put it back on the shelves, WPLG-TV reported.
Ybarra was committed for a psychiatric examination Saturday, the Herald said.