Protein in wheat (6)
I believe the answer is:
gluten
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">protein in wheat</span>' is the definition.<br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for gluten that I've seen before include "Sticky substance" , "Protein in wheat grains" , "Protein present in wheat" , "Protein found in cereals" , "Substance contained in many grains" .)