Supervalu would retain a roughly 20 percent ownership in Save-A-Lot directly after the discount grocery chain is spun off as a separate company, according to a securities filing Thursday.

Supervalu's board of directors recently approved the spinoff, which was originally announced in July.

Supervalu shareholders would directly own at least 80 percent of Save-A-Lot, while the Eden Prairie-based company itself would have no more than a 19.9 percent stake, according to the filing with the U.S. Securities and Exchange Commission. The new Save-A-Lot would be listed separately on the New York Stock Exchange. The filing doesn't say when a spinoff would occur.

Save-A-Lot, which Supervalu has owned for more than 20 years, has more than 1,300 stores nationwide, with the heaviest concentration in Ohio, Florida, Kentucky and Tennessee. Its one Minnesota store is in St. Cloud.

Supervalu has pitched the spinoff as a way to improve management's focus on each of Supervalu's three parts: wholesale groceries, conventional supermarkets like its Cub Foods chain and Save-A-Lot itself.

Stock analysts see the spinoff as a way to unlock value in Supervalu's stock, which has been moribund in recent months. It closed Thursday at $6.16, down 54 cents or 8.06 percent, hitting a 52-week low during the day.

Save-A-Lot, which is based in St. Louis, is in one of the few parts of the grocery business that could be called fast-growing.

It is an ultralow price chain, which relies heavily on private-label goods and competes particularly with Aldi, Wal-Mart and dollar stores. Save-A-Lot, like Aldi, has small stores that are about 17,000 square feet — compared to 50,000 square feet or more for a conventional supermarket.

The chain comprised $4.6 billion of Supervalu's $17.8 billion in sales during its last fiscal year.

Mike Hughlett • 612-673-7003