Lean, juicy and moderately tender beef that is very affordable. This steak has no bones and very little fat, making it taste delicious any way it's cooked. Very thin cut strips of sirloin steak can be nearly as tender as a filet mignon, making it an excellent value. Marinating top sirloin steak will allow certain acids and enzymes within the marinade to loosen and break down the protein bonds within the meat. This mostly happens to the surface of the meat unless you inject the marinade. Certain fruit enzymes are great for breaking down proteins. Kiwis, papayas and Asian pears are some of the most popular marinade ingredients around the world.