Editors' pick: Originally published April 27.

McDonald's (MCD) - Get Report continues to tinker with some of the classic items on its menu as it seeks to improve its sales in the U.S. 

The Golden Arches said Wednesday it started to test Chicken McNuggets with no artificial preservatives in 140 stores in Oregon and southwest Washington in March. According to a source close to the matter, the new McNuggets won't be available nationwide until August.

News of the test was first reported by Crain's

A McDonald's spokeswoman tells TheStreet the new McNugget is still made with 100% white-meat chicken, no artificial flavors or colors and the company's signature seasonings and crispy breading. But, the ones being tested in Portland have no artificial preservatives. 

"Customers in Portland have responded favorably, and we'll continue to learn from this test to inform future decisions," said the spokeswoman. 

So, in effect it looks as it McDonald's has created a "clean" Chicken McNugget. "Clean" ingredients are the new buzzword being used in the fast-food industry in an attempt to address healthier eating trends. A food is commonly referred to as "clean" once it's free of artificial flavors, sweeteners and preservatives.

The McNugget isn't the only iconic food McDonald's has revamped lately. 

A McDonald's spokeswoman recently toldTheStreet the company has begun testing a "Grand Mac" and "Mac Jr." in over 120 restaurants in the central Ohio and Dallas areas. The Grand Mac, which will cost $4.89, is made with two 1/6-pound beef patties on a larger sesame seed bun, compared to a traditional Big Mac, which has two 1.6 ounce beef patties. The Mac Jr. is essentially a single-layer Big Mac that will go for about $2.39 or $2.59, depending on location.