Whenever in the judgment of the department such action will promote honesty and fair dealing in the interest of consumers, the department shall promulgate regulations fixing and establishing for any food or class of food a reasonable definition and standard of identity or reasonable standard of quality or fill of container. In prescribing a definition and standard of identity for any food or class of food in which optional ingredients are permitted, the department shall, for the purpose of promoting honesty and fair dealing in the interest of consumers, designate the optional ingredients which must be named on the label. The definitions and standards so promulgated must conform so far as practicable to the definitions and standards promulgated under authority of the federal act.