Returned surprised comment, captivated by the flavouring (5)
I believe the answer is:
thyme
'flavouring' is the definition.
(thyme is a kind of flavouring)
'returned surprised comment captivated by the' is the wordplay.
'returned' says the letters should be written backwards.
'surprised comment' becomes 'my' (expression of surprise).
'captivated by' indicates putting letters inside.
'my' backwards is 'ym'.
'ym' inserted into 'the' is 'THYME'.
(Other definitions for thyme that I've seen before include "Flavouring" , "Kind of mint" , "something fragrant?" , "Part of song: ''parsley, sage, rosemary and . . . . .''" , "Herb with fragrant leaves - parsley, sage, rosemary and . . . . ." .)