PCC Natural Markets is in search of something sweet: a powdered sugar that's free of ingredients derived from genetically engineered corn to be exact. The certified organic grocer hopes to fill a spot on its shelf left vacant after its previous supplier refused to enroll in the Non-GMO (genetically modified organism) Project Verification Program.

The Non-GMI Project Verification Program is gaining steam with some retailers and manufacturers.

The Non-GMO Project is a collaboration of manufacturers, retailers, processors, distributors, farmers and consumers. Products found to contain less than 0.9% GMOs after completing its verification program qualify for the Non-GMO seal. It serves as the first independently verified, uniform way to assure shoppers that a product is, for the most part, free of GM ingredients.

The Non-GMO Project mark is just now popping up on items ranging from Whole Foods' 365 Everyday Value Tortilla Chips to Guayaki Yerba Mate, but independent claims — touting “contain no GMOs” or “GMO-free” — are nothing new.

In fact, during the 52 weeks ending April 17, packaged foods making these claims accounted for $786.9 million in sales, up 11.9% vs. the same period last year, according to the Nielsen Co., Chicago. GMO-free is also the fastest-growing health and wellness claim touted by private labels. Sales of these items spiked 68% to $53.9 million during the same time period.

A few corporate brands are seeking Non-GMO Project Verification. In addition to Whole Foods' 365 Everyday Value, there are its Whole Foods Brand Products, which are sourced to avoid GMOs; the Meijer Naturals GMO-free line, which includes Chocolate Chip Pancake Mix, White Cheddar Popcorn and Corn & Bean Mild Salsa; and items in the H.E. Butt Grocery Co.'s Central Market natural and organic lines.

The products are currying favor with the 53% of Americans avoiding foods that contain GM ingredients, according to a CBS News/New York Times poll.

These shoppers' selection is somewhat limited since more than 75% of processed foods in the average grocery store contain GM ingredients. Not surprising considering that the majority of soy (91%), cotton (87%) and corn (73%) grown in the U.S. comes from GM crops, according to government statistics from 2007.

The U.S. is different from the European Union since it does not regulate disclosure on products manufactured with GM ingredients. Instead, shoppers choosing to exclude these foods rely on a voluntary labeling system, or purchase foods that have been certified organic since they are not allowed to contain GMOs.

The Food and Drug Administration has issued guidance for manufacturers who wish to label foods as GM-free. But in the absence of set standards, it's difficult for retailers to separate factual claims from fiction.