The most common and most likely answer to this crossword clue is the 8 letter word GELATINE
I've seen this crossword clue in The Guardian
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More clues leading to the result GELATINE
Buddy explains!

The straight part
We know that "food additive" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case food additive = gelatine.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 GELATINE mean?
GELATINE noun- A protein derived through partial hydrolysis of the collagen extracted from animal skin, bones, cartilage, ligaments, etc.
- An edible jelly made from this material.
- A thin, translucent membrane used as a filter for photography or for theatrical lighting effects.