How do food preservatives work?

[Evil Captor]

Frequently in commercially prepared foods, you see preservatives listed -- I'd assume it's stuff like lecithin and monoglobular glutamate or whatever. But I was wondering how they work. Do they dry food out? Sounds like it might have quite the effect on taste and texture. I mean, fresh food does taste better than commercial stuff, but nothing like the difference when you, say, preserve meat by smoking it or salting it.

So how do these babies work without having the same effect as more traditional preservation methods?

[xash]

Here's a starting point:

http://home.howstuffworks.com/food-preservation.htm

[jk1245]

There are basically 3 ways to preserve food (or, I guess you could say, 3 common ways that food spoils):

1) Microbial (bacterial or fungal) growth - antimicriobials are in lots of foods. Sulfites, organic acids, parabens, nitrates and nitrites are the most commonly used ones. These work in the manner of many antimicrobials that you may take for infection, i.e. interfering with some critical cellular function such as DNA or protein synthesis, cell wall degradation and so on.

2) Antioxidants - Usually in the form of butylated-something (BHT, BHA) and used to prevent the breakdown of molecules (esp. unsat. fatty acids) when exposed to oxygen. Simply "soak up" free radicals (i.e. elemental oxygen) to prevent bonding to various chemical bonds common in foods, and very common in fats and oils. If allowed to react, these free radical initaited chemical changes are what cause "rancid" characteristics.

3) Enzyme inhibitors - many foods, but esp. fruits and vegetables have ripening enzymes that continue to work after the product is harvested. Some weak acids (ascorbic) can make the pH low enough to hinder or deactivate these enzymes. Chelators like EDTA remove metal cofactors that many enzymes need to function.

One other thing is that many preservatives act across more than one area. Sulfites show all 3 functions, and most enzyme inhibitors have some antimicrobial activity.

They don't affect taste because they are present in such small amounts. Also, they have been selected for use in the food industry precisely becasue they don't have an appreciable taste at effective levels (well, that and they're safe).

That's it in brief. There are literally textbooks full of more info if you like.

[Evil Captor]

Thanks for the link, Xash and thanks for the informative reply, jk1245. I get it ... the chemicals either kill or inhibit bacteria, but they're present in sufficiently small amounts that they don't affect the taste of the food much.

[Roches]

mm, EDTA. An anecdote follows.

I was at a home show a year or so ago and walked by a booth where someone was selling some kitchen gadget that makes mayonnaise. The demonstrator was holding a jar of commercial mayo (Hellmann's label covered, of course) and asked the audience: "Does anyone know what 'EDTA' is?"

I couldn't resist: "Ethylenediaminetetraacetic acid." (I really like the rhythmic sound of the name, so I try to say it whenever it's justifiable.)

Obviously not having prepared for the eventuality of someone knowing what EDTA was, she ignored me, and someone said "a chemical". This answer was accepted. And, of course, no one wants chemicals (much less chelating agents or preservatives) in their mayonnaise.

It was not mentioned that EDTA (but mostly the use of pasteurized eggs) allows you to not die if you eat mayo that hasn't been constantly refrigerated (for up to a couple days) until immediately before serving.

[dwyr]

Lecithin is more an emulsifier than a preservative. It keeps components from separating out, like the oil in mayo for instance. Lecithin is naturally occuring in egg yolks, a main ingredient in mayonnaise.