I checked out of curiosity.
Citric acid. Preserves a lot of colorful compounds from oxidation.
Back in the early '80s I was lucky to get a job working in a restaurant. Saw an invoice for some commercial product to keep lettuce from "rusting" and was stunned at the price. Told the manager just to get a pound of citric acid. A week later she said it worked the same and cost 1/4 as much. 
These days I usually have a few pounds sitting around. Keeps apples from discoloring, not just lettuce. Add it to the turkey or chicken carcass/bones to get a bit of Ca and P from the bones for the broth--and calcium citrate is readily absorbed by the gut. Great for dissolving water scale from kettles and sinks and dishwashers. Removes rust stains from porcelain. Best of all, if you ingest it, say with apples or such, it just gets kicked into the Krebs cycle.
And if you're eccentric enough and experiment with yellow water as a fertilizer it can balance that to keep from screwing up soil pH. Or if you make soap and spill some of the slop before it sets up or added a bit too much NaOH the citric acid is great for neutralizing the lye.
Edit history
Recommendations
0 members have recommended this reply (displayed in chronological order):
= new reply since forum marked as read