Occasionally saw defect in jelly, for instance (5)
I believe the answer is:
sweet
'jelly for instance' is the definition.
(I know that gelatin dessert is a type of sweet)
'occasionally saw defect' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'saw'+'defect'='sawdefect'
The alternate letters of 'sawdefect' are 'SWEET'.
'in' is the link.
(Other definitions for sweet that I've seen before include "Melodious, not bitter" , "Confection" , "bon-bon" , "Pudding" , "Dulcet - dessert" .)