Is it true that mayonnaise is a major source of foodborne illness?
No. This notion continues to circulate, even on some reputable websites. Granted, summertime picnic spreads that include heaping bowls of potato salad, chicken salad, tuna salad, and egg salad can easily be the source of food poisoning if these foods are left out in the heat. But here’s the thing: Commercial mayonnaise—made primarily of water, vegetable oil, and eggs—isn’t the culprit.
The mayo myth began back when it was more common to make mayonnaise at home, using raw eggs. But commercial mayo doesn’t cause food poisoning for a couple of reasons. One is that it is made with pasteurized eggs, which carry virtually no risk of contamination.
Second, commercially prepared mayo must adhere to what’s known as a “standard of identity” set by the FDA—that is, it must be made with specific ingredients in a specific way. Two of the required ingredients are vinegar and lemon juice, in set amounts. Both are acidic, and acid is the enemy of foodborne bacteria.
In fact, Salmonella, E. coli, Listeria, and other harmful bacteria actually die when “inoculated” into mayonnaise, according to a review of literature published in the Journal of Food Protection in 2000. At the time of publication, there had been no incidences of foodborne illness associated with commercially produced mayonnaise, giving it a “remarkable safety record,” the authors noted. There are no reports directly linking mayo to illness since then, either.
What may be risky are the ingredients commonly paired with mayo, such as chicken, tuna, potatoes, and eggs, which are less acidic and thus more susceptible to bacterial growth. Combine that with temperatures above 40°F/4°C, and any bacteria that may be present will double in as little as 20 minutes. If mayo is part of the dish, bacterial growth is diminished, but mixing mayo with contaminated ingredients won’t make a dish safe.
If mayo dishes, such as chicken salad or tuna salad, are on your picnic menu, bring them in a cooler with ice packs to keep them below 40°F/4°C. And keep in mind that the USDA recommends tossing any perishable foods, such as meat, poultry, fish, eggs, and leftovers, that have been at room temperature for more than two hours.
Do you need to refrigerate mayonnaise itself? Yes, if it’s homemade, but opinions differ about store-bought. The USDA advises refrigerating commercial mayo after opening it (and discarding it after two months, or if it sits above 50°F/10°C for more than eight hours). One concern is that, even if it’s safe at room temperature, it could become contaminated by the foods you mix it into (transferred by the spoon, for example), and those food particles might encourage bacterial growth. Refrigerating mayo also keeps it fresh longer.
