Fast-food menu tests suggest upscale items could be coming to McDonald's, Wendy's

Innovation at fast-food chains doesn't just come in the form of oddly shaped chicken or partnerships with snack foods. Restaurants are now testing a broader array of flavors and quality ingredients.

In a research note Monday, Nomura analyst Mark Kalinowski shined a light on a handful of chains that have been testing more upscale items.

McDonald's recently concluded a regional test of a Pesto Mozzarella Melt in Southern California. The $4.99 sandwich was made with pesto cream cheese, baby spinach and kale, sliced tomato and sliced mozzarella cheese, according to a spokeswoman for the company.

"The pace of innovation at McDonald's seems to be accelerating," Kalinowski wrote. The home of Golden Arches is no stranger to testing out menu items in regional areas. Over the last year, McDonald's has tried out garlic fries; fresh, never frozen beef; and alternative sizes of its Big Mac.

Wendy's, too, has upped its game. The burger chain is testing Truffle Bacon Cheeseburgers and Bacon Truffle Fries in Massachusetts and Tennessee.

Americans' flavor palates are changing and consumers are more willing to try different offerings, Kalinowski told CNBC. Part of this shift is due to the millennial generation, which is often considered more adventurous with food than previous generations.

However, Kalinowski also noted that consumers as a whole are looking for greater quality foods at the right price.

"The Truffle Bacon Cheeseburger and Bacon Truffle Fries sound like menu items that play to Wendy's brand positioning within the quick-service industry: 'a cut above' traditional fast food, yet still fully within fast food," he wrote.

Decelerated same-store sales could also be a possible catalyst for fast-food chains testing potential new menu items. Limited-time offers and quirky stunt foods have a way of bringing customers into restaurants, if they are done right.

Kalinowski told CNBC that a chain like Wendy's could differentiate itself from competition with its truffle burger — which features truffle aioli, truffle parmesan cheese sauce and a buttery croissant bun — and could challenge its rivals to attempt to emulate the creation.

A representative from Wendy's did not immediately respond to CNBC's request for comment.