A livestock or poultry product is misbranded if it purports to be, or is represented, as a food for which a definition and standard of identity or composition has been prescribed by the regulations of the director under Section 18731 unless it conforms to such definition and standard, and its label bears the name of the food specified in the definition and standard and, insofar as may be required by such regulations, the common names of optional ingredients, other than spices, flavoring, and coloring, present in such food.