OK I did some research. In 2011 am Alabama law firm sued taco bell saying there was only 36% beef in their "meat misxture", I guess they didn't win. In 2014 Taco Bell released the list below saying that there was 88% beef in their "meat mixture". On their website, evidently they justify why things are needed, like lecithin, caramel color, cocoa powder, etc.
Taco Meat Filling Ingredients
Beef, water, isolated oat product, salt, chili pepper, onion powder, tomato powder, oats (wheat), soy lecithin, sugar, spices, maltodextrin (a polysaccharide that is absorbed as glucose), soybean oil (anti-dusting agent), garlic powder, autolyzed yeast extract, citric acid, caramel color, cocoa powder, silicon dioxide (anti-caking agent), natural flavors, yeast, modified corn starch, natural smoke flavor, salt, sodium phosphate, less than 2% of beef broth, potassium phosphate, and potassium lactate.