Starbucks Corporation has announced the closure of approximately 600 underperforming company-operated stores in the US, as the next step in its plan to transform the company. ┬á The Seattle-based coffee chain had already announced plans to close 100 US stores. The decision to add another 500 to that figure is the result of ÔÇ£a rigorous evaluation of the US company-operated store portfolio,ÔÇØ the company said.┬á┬á The majority of the store closures are scheduled to occur from now until mid-2009.