McDonald's Corp. is hoping the health-conscious will want to sink their teeth into a new super-lean hamburger that replaces some of the fat with an algae product.

The fast-food giant based in Oak Brook, Ill., announced Wednesday it is test-marketing the 91 percent fat-free burger in 54 franchises in the Harrisburg, Pa., area."We're excited about it and are very optimistic," said Chuck Rubner, a McDonald's spokesman. "They like the taste of the product and they like the fact that it's a low-fat alternative."

The Lean Deluxe quarter-pound burger with condiments has a 10.5 percent fat content and 310 calories. That compares with a 20.7 percent fat content and about 410 calories in McDonald's regular Quarter Pounder.

"That's unbelievable," said Michael Jacobson, director of the Center for Science in the Public Interest, a consumer group in Washington. "Obviously, I'd have to taste it, but it could be the best burger on the market in terms of fat content."

The patty is composed of 90 percent lean beef, 9 percent water and 1 percent seasonings, Rubner said. Carrageenan, a gumlike algae product used in meats and other foods to bind ingredients, is listed as one of its seasonings.

The secret to the hamburger is the carrageenan - hailed by the beef industry as revolutionary - because it binds the patty together much as fat would, said Mary Adolf of the Beef Industry Council of the Meat Board.

The board funded Auburn University work to develop the low-fat beef, and McDonald's was the first to test-market it.

"It's very similar in taste and texture to a standard-type ground beef patty," Adolf said.