Ralston’s Foodmaker unit will not be sold.

A proposed purchase by management of Ralston Purina’s Foodmaker unit, which operates the Jack in the Box fast-food chain, was called off because of “economic conditions in the industry and a decline in earnings” of the unit. The buy-out, estimated by one analyst to be worth $500 million, was to have been managed by Forstmann Little, which issued a terse joint statement with Ralston about the collapse of the deal.