NEW YORK (AP) — Supermarket chains Kroger Co. and Stop & Shop said Thursday they will join the growing list of store chains that will no longer sell beef that includes an additive with the unappetizing moniker "pink slime."

Federal regulators say the ammonia-treated filler, known in the industry as "lean, finely textured beef," meets food safety standards. But critics say the product could be unsafe and is an unappetizing example of industrialized food production.

The Kroger Co., the nation's largest traditional grocer with 2,435 supermarkets in 31 states, also said it will stop buying the beef, reversing itself after saying Wednesday that it would sell beef both with and without the additive.

Earlier Thursday, Stop & Shop said that while the U.S. Department of Agriculture has said the product is safe for consumption, it will stop selling the beef due to customer concerns. Stop & Shop is a unit of Dutch supermarkets owner Royal Ahold NV and operates 400 stores in the Northeast U.S.

The chains joined Safeway, Supervalu and Food Lion, among others, who have said they won't sell beef with the filler.

"Our customers have expressed their concerns that the use of lean finely textured beef — while fully approved by the USDA for safety and quality — is something they do not want in their ground beef," Kroger said in a statement. "As a result, Kroger will no longer purchase ground beef containing lean finely textured beef."

The low-cost ingredient is made from fatty bits of meat left over from other cuts. The bits are heated to about 100 degrees Fahrenheit and spun to remove most of the fat. The lean mix then is compressed into blocks for use in ground meat. The product is exposed to ammonium hydroxide gas to kill bacteria, such as E. coli and salmonella.

Though the term "pink slime" has been used pejoratively for at least several years, it wasn't until early March that social media suddenly exploded with worry and an online petition seeking its ouster from schools lit up, quickly garnering hundreds of thousands of supporters.

The Agriculture Department said last week that, starting next fall, schools involved in the national school lunch program will have the option of avoiding the product.

Wal-Mart Stores Inc., the retail giant that sells significantly more food than any other chain, said Wednesday that its Walmart and Sam's Club stores will begin selling meat that doesn't contain the additive. It did not specify whether it would stop selling beef with the filler altogether. Wal-Mart did not immediately respond to inquiries Thursday.

Other stores have come out in recent days saying either that they never sold beef with the filler or they plan to stop doing so.

"Our ground beef vendors do not use an ammonium hydroxide treatment in their production processes," Target said in a statement. "Any additional questions can be directed to vendors."

Whole Foods, A&P and Costco said they have never sold beef products with the additive.

On Wednesday, Supervalu Inc. — which operates owns stores under the Acme, Albertsons, Cub Foods, Farm Fresh, Hornbacher's, Jewel-Osco, Lucky, Shaw's/Star Market, Shop 'n Save and Shoppers Food & Pharmacy banners — said that customer concern prompted it to stop carrying products containing the filler.

Delhaize America, the U.S. unit of Belgium's Delhaize Group, also said Wednesday that its Food Lion, Hannaford, Bottom Dollar Food and Sweetbay chains have made similar decisions.

And Safeway Inc., which operates the Genuardi's and Dominicks chains, as well as Safeway stores, also said Wednesday that it has announced it will stop selling fresh or frozen ground beef with the filler.