Subject: How Do the Proteases Found in Papaya, Pineapple and Kiwi Tenderize Meat?

I am a 10th grade chemistry student.  I  plan to do an experiment where I place 
the enzyme found in papaya (papain), pineapple (bromelain), kiwi (actinidin) 
and possibly a fig (ficin) on pieces of meat to see which one “tenderizerizes” 
the meat the fastest. 

My first question is:  what is the  approximate concentration/percentage of the 
enzyme found in each fruit?

Per my research, I found that those enzymes are classified as sulhydryl 
proteases and are closely related to the serine proteases.  Both types of  
these proteases break down complex  proteins.  For example, in tenderizing 
meat, papain “breaks down the protein chains and the peptide bonds between 
amino acids found in complex proteins,” also known as collagen.  The serine 
proteases, such as pepsin performs a similar process in breaking down food for 
digestion.

Since these two groups of proteases are closely related, my second question is:

What, if any, are their differences (such as structure, reactions, chemical 
processes/compositions) in a fairly straight-forward  explanation?

Lastly, any reason why papain is the most commonly used commercial tenderizer 
versus the other enzymes?  

Thank you,

Scott

Re: How Do the Proteases Found in Papaya, Pineapple and Kiwi Tenderize Meat?