Adding onions, garlic and other spices to food does a lot more than make meals taste better. Research shows that the spicy cuisine of some cultures developed not because of taste alone—rather, spices hold antibiotic properties that kill bacteria that would otherwise contaminate food.
Garlic, onion, allspice and oregano contain powerful bacteria-fighting compounds and are the most powerful of the antibiotic spices, according to researchers at Cornell University, whose findings were published in the March 1998 Quarterly Review of Biology. Those spices killed all thirty microorganisms they were tested against, including E. coli and Salmonella, two bacteria that cause food poisoning.
Further, the study found a direct link between a country’s climate and the type and amount of spices used in cultural dishes. The researchers theorized that spicy cuisine—which is usually associated with warm-climate cultures and commonly contains high amounts of garlic and onion—may be born of necessity: Food spoils faster in warmer climates, and spices inhibit that.
The researchers noted that chiles and other hot peppers also are common ingredients in dishes in warmer countries; they found that capsicums, a name that refers to various pepper plants, kill up to 75 percent of bacteria in laboratory tests.
Paul Sherman, an evolutionary biologist and professor of neurobiology and behavior at Cornell, and colleague Jennifer Billing analyzed forty-three spices used in more than 4,500 traditional meat recipes from thirty-six countries. The spices ranged from the relatively bland parsley and sage to the more pungent bay leaves and mustard. Spices that don’t have strong antibiotic power—those that kill only 25 percent of bacteria in tests—include white and black pepper, ginger, aniseed, celery seed and the juice of lemon and lime, according to the study.
The researchers also analyzed spice use by individual countries and found that hot spices were commonly used in the warmer climates of Thailand and India, for example, but sparingly or not at all in such cold-climate countries as Norway and Sweden.
In more than 80 percent of Indian recipes, onions, ginger, capsicums and garlic were used more than 76 percent of the time, the researchers found. By contrast, Norwegian recipes called mostly for black and white pepper, and spices were used in only half of the seventy-seven Norwegian recipes studied. Onions were used in a mere 20 percent of those recipes, and peppers weren’t included at all.
The study showed a similar climate-spice correlation for the United States, exemplified by the spicy Cajun food of Louisiana and the blander meals of New England.
The researchers also compared the rate of food poisoning in Japan and Korea, two countries with similar climates but a surprising variation in foodborne illnesses. In Japan, nearly thirty cases of food poisoning for every 100,000 people were reported between 1971 and 1990, compared with only three cases per 100,000 people in Korea. The researchers speculated that the lower number of food-poisoning cases in Korea may be because Korean food is spicier than the more delicate flavors of Japanese cuisine.
According to Sherman, when Japanese recipes were created, fresh fish was perhaps more readily available and fewer spices were needed to kill bacteria. But today, he says, fish may not be as fresh, and the original, non-spicy recipes may be insufficient to kill bacteria, so more food poisoning occurs.
Although the Cornell researchers acknowledge that spices are used foremost as flavoring, they say that spices ultimately are used to rid foods of pathogens, leading to the good health and survival of the people who use them.
“There’s a correlation between what tastes good and what’s good for you,” Sherman says.
Spice use evolved by people watching and imitating how others prepared their food, he says. When people eating spicy foods weren’t getting sick as often as their neighbors who ate spice-free food, spices were incorporated into the cuisine, and the culture developed a taste for them.
And it seems that the more spices used on food, the better. The researchers found that combined herbs may have more powerful antibiotic effects than herbs used alone. Such combinations include chili powder, made up of red pepper, onion, paprika, garlic, cumin, and oregano and five-spice powder, which contains pepper, cinnamon, anise, fennel and cloves.
“Blends used habitually together may be especially potent synergistic combinations,” says Sherman, adding that white and black pepper and the juice of lemon and lime are notable synergists and increase the effectiveness of other spices.
Take salsa, for example. Loaded with hot peppers, onions and garlic, this spicy sauce typical of warm-climate cuisines is a microorganism’s nightmare because of each spice’s ability to fight bacteria. Add a squeeze of lime and you’ve got a really potent blend.
Antibiotic compounds evolved in plants to deter threatening invaders such as fungi, bacteria and insects. These secondary compounds aren’t required for the plant’s basic metabolism but do contribute to its flavor and are the result of an evolutionary protection response by the plant, Sherman says.
“We’re using the plants’ recipes in our own recipes, and for
basically the same purpose,” he says.