Orange-based Merical Inc. has been acquired on undisclosed terms by private-equity firm Linden Capital Partners LLC in Chicago.

Linden named its Operating Partner Brian Smith interim Chief Executive of Merical. Smith was most recently Chief Executive of First Engineering, a global provider of finished medical devices. Linden Operating Partner Chris Kolber also has joined the Merical board.

Merical makes and packages probiotic and nutritional supplements. The 51-year-old firm employs 400 companywide. It benefits from Linden’s healthcare network and expertise in manufacturing and pharmaceutical operations, said Jeff Stallings, Merical president.

Linden is a middle-market private-equity investment firm that has approximately $1.3 billion in assets. It does leveraged buyouts in healthcare and the life sciences.