Cat trio ruined dairy product (7)
I believe the answer is:
ricotta
'dairy product' is the definition.
(ricotta is a kind of dairy product)
'cat trio ruined' is the wordplay.
'ruined' indicates an anagram.
'cat'+'trio'='cattrio'
'cattrio' is an anagram of 'RICOTTA'.
(Other definitions for ricotta that I've seen before include "One soft cheese" , "Read the riot act about the cheese" , "cheese found" , "Soft white cheese used in Italian cooking" , "Cheese - Riot Act (anag)" .)