Sticky substance found in 50% of raw vegetables (4)
I believe the answer is:
crud
'in 50% of raw vegetables' is the definition.
I can't judge whether this defines the answer.
'sticky substance' is the wordplay.
'sticky' becomes 'cru' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'substance' becomes 'D' (D is an example).
'cru'+'d'='CRUD'
'found' is the link.
Can you help me to learn more?
(Other definitions for crud that I've seen before include "worthless stuff" , "Unpleasant substance" , "Disgusting waste matter" , "radioactive waste" , "Disgustingly foul substance" .)