DEAR DR. BLONZ: Is it best to stick with foods that say "no preservatives added" on the label? -- F.F., Los Angeles
DEAR F.F.: If we only ate farm-fresh products, we would have little need for food preservation beyond a refrigerator. But most of us aren't fortunate enough to have that as an option. Instead, we have to rely on methods of food preservation designed to deal with the reality that the nutrients in foods are just as attractive to microorganisms as they are to us.
Here are some examples, many of which are based on the fact that water is as essential to spoilage organisms as it is to humans.
Drying is the most basic method, in that it removes water. Sugaring or salting work through an ionic effect that can draw water out of the spoilage organisms and prevents their growth. Freezing slows down the spoilage process by changing that water into ice crystals, which cannot be utilized by most bacteria. The canning process destroys organisms through heating, and then places food in a sealed container to prevent further contamination. Pasteurization destroys most existing spoilage organisms by heating the food to a high temperature for a short duration.
Pickling (or fermentation or culturing) leaves the food with a higher level of acid, creating an inhospitable environment for certain types of spoilage organisms. Smoking adds smoke-born chemicals to a food that help destroy potential organisms.
Finally, there is the use of chemical additives designed to either destroy spoilage organisms or inhibit their growth. Antimicrobial preservatives are special chemicals that can stop the growth of bacteria, molds, fungi and yeast that destroy food. Antioxidant preservatives prevent rancidity, "off" flavors and discoloration caused by oxidation.
Chemical preservatives get mixed reviews. Some are essentially harmless in the minute quantities used, while others have an inconsistent safety record. Nature serves as our best instructor, as many commonly used preservatives are based on natural substances.
Tocopherol (vitamin E) compounds are used in nature to protect plant seed oils, and ascorbates (vitamin C) help keep fruits and vegetables fresh. Both are natural antioxidants. Fruits, such as cranberries, raisins, prunes and citrus, contain natural acids that make effective antimicrobial agents. These compounds include citrate, propionate, benzoate, sorbate and lactate.
Raisin juice is a natural source of propionate, a compound used by bread makers to help slow the formation of molds. The bakers have the option of using raisin juice (natural) or adding calcium propionate (artificial) to inhibit mold in their products. In either case, these compounds and others like them are harmless at the levels used.
Some preservatives have less than glowing safety records. Among these are the sulfites and nitrites. Sulfites are effective antioxidants, but the U.S. Food and Drug Administration estimates that as many as 100,000 people in the United States react badly to sulfite preservatives. If you are among them, eating foods with sulfites might cause symptoms like headache, hives or shortness of breath. If sulfites are present, the food's label must say so.
Processors put nitrites in sausages, bacon and other cured meats because they inhibit the bacteria responsible for botulism poisoning. In the body, nitrites can be converted into nitrosamines, compounds known to cause cancer in animals. In making a choice between the possible dangers of botulism and nitrosamines, nitrite preservatives are deemed the lesser of the two dangers. Still, it makes sense to limit our consumption of nitrite-containing meats.
It is perceived as desirable for food labels to say "no preservatives added," but we should realize that not all preservatives are of concern -- especially ones based on naturally occurring substances. There's little value in keeping foods preservative-free if half the product gets discarded due to spoilage, or, worse, if you end up eating food that has already begun to spoil.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.