The companies did not specify financial details. Grotech Capital Group and Leonard Green & Partners also acquired a stake.
Del Taco was founded in 1964 and operates 460 restaurants selling Tex-Mex fare, burgers and fries, primarily in Western states. The Lake Forest, Calif. company trails only Taco Bell among Mexican fast-food chains, which has more than 6,500 locations.
The investment was made through Boston-based Charlesbank portfolio company Sagittarius Brands, the Nashville, Tenn., parent of Captain D's Seafood. The deal gives Sagittarius annual sales in excess of $1 billion annually.
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