If you want to know what Taco Bell actually uses in its "beef" products, here's an ingredients list of their "Taco Meat Filling," courtesy of Gizmodo:
"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 percent of beef broth, potassium phosphate, and potassium lactate."
The filling also includes 36 percent beef. The other 64 percent consist of the ingredients listed above.