Chose about fifty to have preserved (7)
I believe the answer is:
pickled
'preserved' is the definition.
(pickling is a kind of preserving)
'chose about fifty' is the wordplay.
'chose' becomes 'picked' (picking is a kind of choosing).
'about' indicates putting letters inside.
'fifty' becomes 'L' (Roman numeral).
'picked' going around 'l' is 'PICKLED'.
'to have' acts as a link.
(Other definitions for pickled that I've seen before include "Drunk (as a gherkin?)" , "Soused" , "Brahms and Liszt" , "Preserved - drunk" , "Blotto" .)