Can't imagine any of the coloring/ flavoring/ preservative agents would be beneficial to bonding strength. Protein powder is generally derived from either whey (milk) or soy. Both are readily available, without the undesirable ingredients, at a much lower cost than their by-product dietary supplement powders. But rather than re-inventing the wheel, why not just buy some rawhide? Or a dog bone? Or purchase pre-made hide glue?