Mastroianni was released by the Twins on Tuesday, Mike Berardino of the St. Paul Pioneer Press reports.
The veteran appeared in only seven games for the big league club this season, failing to notch a hit in 11 plate appearances. He spent the bulk of the year at Triple-A, but with Byron Buxton back at Rochester, Mastroianni's services were no longer needed. The career .206 major league hitter will now look to latch on with another organization, likely on a minor league deal.