Blackstone Group LP will score about a 300 percent partly realized gain on Pinnacle Foods Inc.’s $6.6 billion sale to Hillshire Brands Co., as private-equity firms capitalize on a surge in asset values to unload holdings.

The world’s biggest manager of alternative assets, which owns 51 percent of Pinnacle, will receive $1.1 billion for its Pinnacle shares and Hillshire stock valued at $1.1 billion, based on Hillshire’s closing price Friday of $36.95. It acquired the foodmaker for $2.2 billion seven years ago using a combination of equity and debt.

The sale adds to a series of exits that helped Blackstone return $11.5 billion to investors in its private-equity, real estate and hedge funds last quarter. The New York-based firm, which manages $272 billion, last month reported a 30 percent increase in first-quarter profit as the carrying value of its holdings increased and it collected more fees.

Blackstone originally invested $414.2 million of equity in a leveraged buyout of Parsippany, N.J.-based Pinnacle. The sellers were the private-equity arm of JPMorgan Chase & Co. and JW Childs Associates LP, a Boston-based buyout firm.

Blackstone boosted its investment by $260 million to $674.2 million when Pinnacle acquired Birds Eye Foods LLC in 2010. It sold a fraction of its Pinnacle shares in December for $503.3 million and has taken at least $53.8 million in dividends from Pinnacle, which owns the Birds Eye, Duncan Hines and Vlasic food brands, according to regulatory filings.

Peter Rose, a Blackstone spokesman, declined to comment.

Pinnacle’s sale to Hillshire is expected to close by September, Hillshire said in a statement.