Police are investigating food tampering at three different Sobeys stores in Calgary. (CBC)

Metal items have been found in various food items at three different Sobeys grocery stores in Calgary, the second chain hit by tampering this year.

On Tuesday, a woman found a metal item in an avocado she purchased at the Sobeys at 150 Millrise Blvd S.W., said police.

Over the weekend, metal items 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, the customer bit into the bun but was not hurt.

Calgary police said Wednesday that they're investigating all three Sobeys cases.

Last week, a woman was charged with mischief over $5,000 in connection with metal pins 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. Pins were found in bakery items, cheese, juices and bulk foods in January and February.

Police said they're still investigating those incidents.

Until they close the cases, investigators urged the public to inspect all food purchased from grocery stores to ensure the items are safe.