A Safeway at 70 Shawville Blvd. S.W. is the latest target in a series of food tampering incidents at major grocery store chains. (CBC)

A $10,000 reward is being offered for the arrest and conviction of those responsible for a series of food-tampering cases in major grocery chains in Calgary over the past three months.

The Canadian Council of Grocery Distributors, which represents grocers that have been targeted, including Safeway, Co-op and Sobeys, announced the reward on Tuesday.

Safeway became the third grocery chain in Calgary to be the target of food tampering after a piece of metal was found in a loaf of bread.

So many cases of food sabotage have occurred in Calgary since January that police are warning people to thoroughly inspect all food, no matter where it's bought.

"Although there is an individual out there doing these types of things, we all have the ability to check our own food products," said Duty Insp. Vic Trickett of the Calgary police. "The control still remains with us."

Police were called to the Safeway at 70 Shawville Blvd. S.W. Monday after a customer reported finding the tampered bread purchased the day before. Investigators did not reveal what the object was but believe it was inserted into the bread inside the store.

"You could see where the exterior plastic wrapping had been penetrated so it would appear that the metal object was inserted through the plastic and embedded into the bread," said Kevin Brookwell, a Calgary police spokesman.

Extra security had already been in place for several weeks after food-tampering incidents at Calgary Co-op and Sobeys stores, said Canada Safeway spokeswoman Betty Kellsey.

Pins were found in baked goods, cheese, juices and bulk foods twice in January and February at the Calgary Co-op in Oakridge Centre in the southwest.

A woman was charged earlier this month with mischief over $5,000 after metal pins were found again in packaged food items at the same store on March 11.

Metal objects were found in produce as well as two kaiser buns at Sobeys stores in the south of the city.

All the cases of food tampering are now being handled as one investigation, Trickett said.

The continued rash of food tampering is frustrating, Trickett said, but he added: "I am quite confident that we will be successful and we will find the individual or individuals that are responsible for this."

Several shoppers leaving the Safeway store Tuesday said the incidents have prompted them to be more vigilant about their purchases.

"I check my groceries. It's about all you can do," said Jackie Dyer. "Fruits, vegetables, bread — I take care a little bit more."

With files from Peter Akman