Protein present in wheat (6)
I believe the answer is:
gluten
'protein present in wheat' is the definition.
(I've seen this before)
This is all the clue.
(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" .)