Poultry company Perdue Farms will buy natural meat maker Niman Ranch, which is Chipotle Mexican Grill's biggest pork supplier and a brand name on U.S. restaurant menus, the two companies said on Tuesday.

Privately held Perdue expects to "soon" close a deal to buy Natural Food Holdings, which owns the Niman Ranch brand, from private equity firm LNK Partners, according to a statement. Terms were not disclosed.

“This represents the next chapter in our growth through premium proteins and trusted brands,” said Perdue Farms Chairman Jim Perdue. “The Niman Ranch brand continues our commitment to raising animals without antibiotics or artificial growth stimulants, and to responsible food and agriculture.”

The deal marks the latest move by a big food company seeking to expand its presence in the fast-growing U.S. natural foods market. It risks displeasing some consumers, who are attracted to Niman Ranch's reputation for working with independent farmers and raising animals without antibiotics.

Niman Ranch plans to continue producing animals in the same way after the deal closes, said Jeff Tripician, chief marketing officer. There is more opportunity for Niman Ranch to grow with Perdue than with LNK, he added.

LNK Partners, a private equity firm, is selling Natural Food Holdings to Perdue for an undisclosed amount. The two companies signed a definitive agreement for the sale and expect to close the transaction soon.

Niman Ranch began in the early 1970s on a small ranch in California, and has grown to include more than 700 independent family farmers and ranchers, spread across the country. The Niman Ranch brand covers a complete line of pork, beef, lamb, cage-free eggs and a variety of smoked and cured meats. All products are sourced from animals raised to high welfare standards and without any antibiotics.

“With the long, family-owned heritage of our company, we understand and respect what Niman Ranch represents,” said Jim Perdue. “All Niman Ranch livestock will continue to be raised by the same small family farmers and ranchers, following the same protocols, and with the same focus on sustainability.”

“We are excited to become part of Perdue,” said Jeff Swain, Natural Food Holdings’ Chief Executive Officer. “With Perdue being a family-owned business and the Perdue commitment to responsible food and agriculture, it was the perfect fit to help us continue to grow and prosper while staying true to our brand’s mission.”

Through the acquisition, Perdue also acquired the Prairie Grove brand and the SiouxPreme Packing plants in Sioux City and Sioux Center, Iowa.

“This is more than adding volume and capacity,” said Randy Day, President, Perdue Foods. “This acquisition is an important step forward in growing our pork business through premium brands with high standards for animal welfare and sustainable agricultural practices. We hope to grow the number of family farmers in the Niman Ranch network, and expand distribution into more cities across the country, thereby reaching more consumers and providing greater access to sustainably produced meat.”

“We want to become better, not just bigger,” said Perdue. “The acquisition of Natural Food Holdings supports our direction forward as we continually elevate our products and production practices.”

“The promise of each of the brands, our relationship with family farmers and the value we bring to customers and consumers will not change,” said Day. “Through this merger, we’ll learn from each other to get better at everything we do.”

This year, Niman Ranch ramped up shipments of pork to Chipotle when another producer ran afoul of the burrito chain's animal welfare rules.

A Chipotle spokesman did not immediately respond to requests for comment about the sale.

Perdue, a supplier to Chick-fil-A restaurants, already produces antibiotic-free chicken and acquired Coleman Natural Foods in 2011.

The acquisition is another step in Perdue’s transformation into one of the largest suppliers of premium meats. Restaurants and food companies are clamoring for such meats, as consumers increasingly demand less reliance on pharmaceuticals and better animal welfare.