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Re: Is it safe to leave food in the cans they came in? » KaraS

Posted by Larry Hoover on March 31, 2005, at 10:34:03

In reply to Is it safe to leave food in the cans they came in?, posted by KaraS on March 27, 2005, at 23:23:43

> Sometimes if I've opened a can and only consume part of it contents, I'll keep the food in the can and put some tin foil over it and then refrigerate it. Is this dangerous? Is aluminun leaking into the contents of the can or is some other bad reaction taking place?

Sorry, I didn't know this thread was active, here in the bowels of Babble-land....

I did a year-long research project on potential toxicities/endocrine disruption which might arise from canned foods.

There are two sorts of cans. One is based on steel (the ones with a seam up the side, and ones based on aluminum (no side seam). Either one might be lacquered, to seal the metal against direct contact with the food.

The regulations which control food safety are designed to ensure that food stored in *sealed* cans does not become contaminated by bacteria, or pick up contaminants from the container itself. No provision is made for examining the effect of leaving the contents in an opened can. It's not part of the food safety standards, and it's assumed it does not happen.

However....

Some cans have obvious lacquer layers inside them. They may be opaque white, or the metal will shine from behind a slightly opaque surface. These tins are least likely to permit leaching from the can wall into the food.....of the metals behind the lacquer. The effect itself depends on time exposed to air. There is no air in a sealed can, which is the reason it remains stable so long. Add air, and the chemistry changes altogether.

I made a point of mentioning leaching of the metal behind the lacquer. You may also have leaching of the lacquer itself. I last looked at the literature about eight years ago, and at that time, there was significant concern about lacquer chemicals appearing in food. The European Union passed some strict legislation in that regard, and because of global trade, I would presume that everybody simply adopted those new regs (or you can't trade your product internationally).

There had been a significant issue of plastic monomers leaching into food, as the lacquer coatings were applied after the can was formed, via in situ polymerization. The efficiency of the polymerization process seemed to be no better than 88%, leaving the remainder to leach into food. I think they got that figure up to 96%, but that's as I recall it.

Anyway, leaving food in these tins after opening is creating a whole new chemical environment, with oxidizers leading the way. The oxidizers massively promote decomposition of the lacquer, and if there is the slightest imperfection in the lacquer seal, the metal of the container itself. The oxidation process forms free monomer/dimers (and other fragments), as well as soluble metal cations, which move into the aqueous food environment.

Here's a thinking point. Would you save empty (washed) tins to later use as food storage containers?

I think you can use the latter question to clear up any lingering doubt.

Lar

 

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