I have used papain with some marinades for goat meat. Personally I do not care much for marinades any more, at least not long ones.
For example, I used to marinate chicken overnight with spices and yogurt when making chicken tikka or tandoori chicken. Guests would rave about how tender and soft the meat was, when to me it was mushy. I didn't care for it that much. I prefer to marinate my chicken for about 4-6hrs now.
The same goes for my goat meat items. I don't marinate overnight anymore. I don't miss the papain, because the meat would turn to mush and I didn't care for the texture. I am speaking in the context of Indian recipes (the country, not Native American) so YMMV.
Having said that, give it a try and report back. What fun would any of this be without experimentation and trying something new now and then?
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