How salt cures.

How salt cures

For millennia, cooks have used salt to preserve meats and other perishables. But to this day the scientific understanding of how salt inhibits food spoilage is still sketchy, says microbiologist Robert L. Buchanan at the U. S. Agriculture Department's Eastern Research Center in Philadelphia.

Because of concern about the risk of high blood pressure that salt may pose, the federal government is trying to get processed-food manufacturers to reduce the sodium chloride they use by 25 percent. It has become the job of Buchanan and his co-workers to find out how salt, and its reduction, might affect this food's safety.

Recent findings by the group indicate that because high levels of salt are toxic to most cells, bacteria settling on salted meat will absorb the salt and then have to spend a lot of energy pumping it out again. In some bacteria, this salt-mediated energy drain has been high enough to make them shut down nonessential activities, like producing toxins.

Buchanan has also found that sodium chloride reduces bacteria's ability to feast, further exacerbating the energy drain. An incubation medium containing 4 or 5 percent salt will reduce the bacteria's uptake of the untrient glucose by 50 to 75 percent. When the salt level is lowered to 2.5 percent, he says, glucose uptake is inhibited by only about 20 percent. Under study is whether salt also alters the success of negatively charged bacteria in adhering to positively charged meat surfaces by a process analogous to short circuiting.