Archive for Wednesday, June 2, 2004

Mayonnaise can help reduce salmonella risk

June 2, 2004


Don't we really have to watch out for salads that have mayonnaise in them?

For decades, mayonnaise has been blamed for salmonella in potato, pasta and meat salads. To the contrary, University of Georgia food scientists have found that commercially-prepared mayonnaise actually reduces the amount of salmonella in foods.

Food scientists at the University of Georgia Center for Food Safety, working with their counterparts at the University of Wisconsin, studied salmonella and commercially-produced mayonnaise.

Cases of salmonellosis linked to mayonnaise have most often occurred in Europe where homemade mayonnaise is commonly used. Europeans often make homemade mayonnaise using eggs and oil, but not enough vinegar.

The eggs are unpasteurized, and the mayonnaise lacks the important acid content that vinegar provides.

The U.S. Food and Drug Administration regulates the amount of acid mayonnaise makers must add to their products. This acid comes from the vinegar and lemon or lime juice.

Once these ingredients are emulsified, the final product's pH, water activity, and sodium chloride content create a hostile environment for harmful bacteria. As a result, salmonella can't survive in commercial mayonnaise.

However, once mayonnaise is blended with other foods, like the ingredients for potato, pasta, or chicken salad, that's when bacteria begin to grow.

In lab tests, the food scientists added mayonnaise to foods inoculated with salmonella. The number of salmonella cells declined immediately after the bacteria was added to either chicken or ham salad that contained commercial mayonnaise.

Refrigerating the salads kept salmonella from growing, too. Neither the ham nor the chicken salad had increased numbers of salmonella cells up to 24 hours after refrigeration. The meat salads also were tested at room temperature. After five hours, both showed "relatively little growth" of salmonella cells.

Further tests showed that salmonella growth slows as the amount of mayonnaise is increased.

Overall, the research has shown that mayonnaise helps slow the growth of salmonella in most meats and poultry. Mayonnaise reduces the rate at which these bacteria can grow.

However, it is best not to hold perishable foods, even those that contain commercial mayonnaise, at room temperature for more than two hours. Mayonnaise will not maintain its acidity level very well over time when mixed with other less acid foods like meats, poultry, eggs or potatoes. Bacteria can begin to multiply if these foods are allowed to remain between 40 and 140 degrees. Always keep salads such as these at refrigerator temperature.

For safety and the best quality, refrigerate the mayonnaise, too.

The more times you open the jar and remove some of the product, the more chances there are for moisture, food particles or mold spores to enter the mayonnaise. This could cause changes in the mayonnaise itself, especially at room temperature. Using a clean knife or spoon each time, will make food particles less likely to get into the jar.

Does reduced-calorie mayonnaise also slow the growth of salmonella?

The University of Georgia Center for Food Safety researchers also studied reduced-calorie mayonnaise, which contains more water and less vinegar and oil. They found it also slows salmonella growth, but not as much as regular mayonnaise.

To separate the egg yolk from the white, I pass the egg yolk back and forth from shell half to shell half. Is this the best way to separate eggs?

No, it's not. Bacteria are so very tiny that, even after washing and sanitizing, it's possible that some bacteria may remain in the shell's pores. The shell might also become contaminated from other sources. When you break or separate eggs, it's best to avoid mixing the yolks and whites with the shells. Rather than broken shell halves or your hands, use an inexpensive egg separator or a funnel when you separate eggs to help prevent introducing bacteria. Also use a clean utensil to remove any bits of eggshell that fall into an egg mixture and avoid using eggshells to measure other foods.

Are soft meringue pies safe to eat?

Yes, if they are prepared properly. Bake a three-egg white meringue spread on a hot, fully cooked pie filling in a preheated 350-degree oven until the meringue reaches 160 degrees, about 15 minutes. For meringues using more whites, bake at 325 degrees (or a lower temperature) until a thermometer registers 160 degrees, about 25 to 30 minutes (or more). The more egg whites, the lower the temperature and longer the time you need to cook the meringue through without excessive browning. Refrigerate meringue-topped pies until serving. Return leftovers to the refrigerator.

Why do some hard-cooked eggs have a greenish ring around the yolk?

The harmless greenish ring is due to an iron and sulfur compound which forms when eggs are overcooked or not cooled quickly.

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