Hi Shelley,
Great question. It really depends on the time the poultry is being marinated, and much of the actual data is proprietary. I've struggled to find publicly available studies in PubMed/Google Scholar. My rule of thumb for most protein marinades is 15-16% across the board, assuming you're marinating for at least an hour under refrigeration. It may be less if you're brining for a shorter time, but you're still within the tolerances of nutrient reporting. Small caveat, I don't know if this rule applies as well with enhanced proteins.
America's Test Kitchen has some good data as well, but it's become paywalled.
One imperfect but useful way to check how much marinade is used is to weigh/measure the amount of marinade going into the protein and how much is left after the protein is removed. It will give you a starting point for the other ingredients in the brine/marinade as well.
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Lesley Schatz
Apex NC
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