Julleen Marter, 47, discovered the object when she poured the sauce into a pan last Thursday and noticed chunks of grey matter floating in it, the Daily Mail reported.
The brain-like object measured 10 cm in diameter, the report said.
"After pouring the tomato passata in, I noticed the consistency was not as it should be. I also noticed the normally bright red sauce was turning a really horrible black colour," the Daily Mail quoted Julleen as saying.
"I realised that there was something in the bottom of the carton so proceeded to cut it open with scissors and to my horror discovered something which I can only describe as strange," she added.
Julleen, a mother of three, said she was waiting for the Environmental Health Office for testing the alien object.
"I am not sure if it was animal or plant but it looks like a brain-type material. At the moment it is frozen because that is what Environmental Health told me to do. I'm waiting for them to come back to me to take it away and have it tested," Julleen said.
"I have examined the object and it certainly isn't a tomato. It's spongy and looks like a small brain," she added.