Although it plans to keep its Longmont, Colo., turkey hot dog processing plant, Butterball LLC , Garner, N.C., sold itsLongmontbrand toSigma Alimentos, one of Mexico's largest refrigerated and frozen food processors and distributors. Terms were not disclosed. . . Encouraged by its success with SUBWAY Restaurants, vending sales and growing interest in its single-serve milks,Shamrock Farms, Phoenix, said it plans to more widely distribute its flavored, on-the-go products and become a true national brand.