Protein present in wheat (6)
I believe the answer is:
gluten
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">protein present in wheat</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for gluten that I've seen before include "Protein found in cereals" , "Protein in grain that gives cohesiveness to dough" , "Protein source" , "Protein left after starch is removed from cereal grains" , "Substance contained in many grains" .)