Calgary police are telling people to carefully inspect any food they purchase following three new cases of food tampering. (CBC)

Sobeys grocery chain says it didn't call in police right away when metal objects were found in some food earlier this week in Calgary because the company didn't think two initial incidents were related.

The company said it has now increased security after the food tampering incidents at three separate stores in the city's south end.

Metal objects were found in two kaiser buns bought from the Sobeys at 20 McKenzie Towne Ave. S.E. and 356 Cranston Rd. S.E.

In one of those cases, a customer took a bite of the bun she bought on Saturday, but didn't suffer any injuries. Then on Tuesday, a woman found some metal in an avocado she purchased at the Sobeys store at 150 Millrise Blvd. S.W.

A spokesman for Sobeys said the company learned of the first two incidents on Monday but waited until the next day to call police.

The chain believed the incidents were not related and it wanted to investigate further, according to Mike Lupien.

"When the third item popped up, that's when we chose to bring in the police. And I should mention that after the second incident, we did bring in the Canadian Food Inspection Agency," he said.

He did not say what the metal objects were, but said the items were different in each case.

'We don't know if it could be a current employee, an ex-employee, disgruntled customer.'—Police spokesman Kevin Brookwell

Police said the public should check their food carefully no matter where they shop. "We don't know if it could be a current employee, an ex-employee, disgruntled customer," said police spokesman Kevin Brookwell.

A woman was charged last week with mischief over $5,000 after metal pins were found in packaged food items at the Calgary Co-op in Oakridge Centre on March 11.

The store was the target of several other incidents of food tampering, which police continue to investigate. Pins were found in bakery items, cheese, juices and bulk foods in January and February.

Lupien said Wednesday it has increased security and is doing more inspections in the wake of the new tampering incidents.

"They are doing regular reviews, walk arounds of the store, and reviews throughout the day of the store and items in it — with particular attention to the fresh areas, meat, produce, bakery items," he said. "We also added extra security guards to the stores in the south Calgary area."

Domenic Pedulla, president of the Canadian Food Safety Group, said you can never go too far to ensure food safety — but it comes at a cost to consumers.

"If we wanted everything produced with a security guard standing over every piece of food that was made for us, for sure we could have it. And I'm sure there'd be lots of people out there that would love to deliver it but [your] package of hot dogs would go from $4 to $40."