Answer: I took the following from the U. S. Department of Health and Human Services Public Health Service (Food and Drug Administration)1999 Food Code regarding materials that can be used in food preparation (commercial, I presume), web site: http://vm.cfsan.fda.gov/~dms/fc99-4.html
4-101.15 Galvanized Metal, Use Limitation.*
Galvanized metal may not be used for utensils or food-contact surfaces of equipment that are used in contact with acidic food.
I spent quite a bit of time searching the Internet for a definitive answer, but did not come up with one. However, there were various suggestions not to use galvanized metal for collecting soil samples (because it might contaminate them), mixing seedstarting mix (because it would react with the acidic peat), and not using them in food preparation. I saw recommendations for using galvanized metal for ornamental flowers, but I didn't find anyone recommending it for food crops -- though that probably doesn't mean much.
Plant roots do create organic acids which could, I suppose, leach the zinc coating from the galvanized metal. Wheter or not the plant would take up the zinc in harmful amounts I don't know.
On a different note, I might be concerned that the pots would heat up dramatically in the sun, and "cook" the plant's roots.So this might be a good reason to choose a material that wouldn't heat up quite so much.
Sorry I can't be more definitive. Before making any big changes, you might try contacting the soil science department at Cornell and see if they have any advice. (If you find anything definitive, I'd appreciate it if you could forward the information to me.)
Q&A Library Searching Tips