Activist hedge fund Jana Partners LLC has disclosed a 9.1% stake in Pinnacle Foods Inc. , a packaged foods company whose brands include Duncan Hines baking mixes and Birds Eyes frozen vegetables. In a filing Thursday, Jana said it acquired the shares because it believes they are "undervalued and represent an attractive investment opportunity." The hedge fund plans to have "discussions" with Pinnacle's board members and executives "regarding value-creation measures," that could include evaluating a sale or other "consolidation opportunities," it said.