By "comparative" do you mean the form of the word that you use when comparing two subjects with that attribute? If so, there is no comparative form. Just use "more" or "less" with the word.
"Oatmeal is more nutritious than sugar." (note the spelling of nutritious)
"His novels are more tasteful than his song lyrics."
Note: the word "tasteful" is not used to refer to food or flavor in Standard American English. Rather, it is used to describe items or events that are "in good taste" which means they are not in any way offensive and would appeal to someone with good education and/or social class. When something is "in bad taste" or "shows bad taste" it means it is offensive or inappropriate.
"There was rock and roll music at the funeral, but it was very tastefully done."
"Her personality was outrageous, but her clothing was perfectly tasteful."
"Howard Stern may not be evil, but his radio show is frequently in bad taste."