Differentiate between Whey Isolate and Soy Protein Isolate

Hi friends,

Now I have one question more, lets say we I purchased a protein powder which is proclaimed as WHEY Isolate . Now is there any way to distinguish or know that it is really whey isolate but not soy isolate. It is because if I am taking soy isolate then still I will see the result but soy isolate is way cheaper than whey isolate.

I mean, is there anything like taste, look or feel of soy isolate which can help me to distinguish between whey and soy isolate ?