The most common and most likely answer to this crossword clue is the 7 letter word CITRATE
I've seen this crossword clue in The Daily Telegraph
C
I
T
R
A
T
E
Buddy explains!

The straight part
We know that "Salt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case salt = citrate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CITRATE mean?
CITRATE noun- Any salt or ester of citric acid.
- To cause to form citrate.