Antimicrobials: the Spice of Life

Ithaca, NY (3/11/98)- The palate-searing spices that make salsa sizzle and Thai food tingle perform a valuable antimicrobial function in cultures traditionally lacking refrigeration, according to a new study from Cornell University.

Researchers have long believed human diet has evolved in response to different cultures' needs. There is now increasing evidence that there are other factors involved than simply improving flavor or covering up the stink of old meat.

 "The proximate reason for spice use obviously is to enhance food palatability," says Paul W. Sherman, an evolutionary biologist and professor of neurobiology and behavior at Cornell. "But why do spices taste good? Traits that are beneficial are transmitted both culturally and genetically, and that includes taste receptors in our mouths and our taste for certain flavors. People who enjoyed food with antibacterial spices probably were healthier, especially in hot climates. They lived longer and left more offspring. And they taught their offspring and others: 'This is how to cook a mastodon.' We believe the ultimate reason for using spices is to kill food-borne bacteria and fungi."
 
Jennifer Billing, also at Cornell, compiled than 4,570 recipes from 93 cookbooks representing traditional, meat-based cuisines of 36 countries; the temperature and precipitation levels of each country; the horticultural ranges of 43 spice plants; and the antibacterial properties of each spice.

These studies showed that garlic, onion, allspice and oregano were the best all-around bacteria killers (they kill everything), followed by thyme, cinnamon, tarragon and cumin (any of which kill up to 80 percent of bacteria). Capsicums, including chilies and other hot peppers, are also potent,  killing or inhibiting up to 75 percent of bacteria), while pepper of the white or black variety inhibits 25 percent of bacteria, as do ginger, anise seed, celery seed and the juices of lemons and limes.

"Countries with hotter climates used spices more frequently than countries with cooler climates. Indeed, in hot countries nearly every meat-based recipe calls for at least one spice, and most include many spices, especially the potent spices, whereas in cooler counties substantial fractions of dishes are prepared without spices, or with just a few," notes Billing. As a result, the estimated fraction of food-spoilage bacteria inhibited by the spices in each recipe is greater in hot than in cold climates, she said.

Thailand, the Philippines, India and Malaysia top the hot food/hot climate chart, while Sweden, Finland and Norway are at the bottom. The United States and China are somewhere in the middle, although the Cornell researchers studied these two countries' cuisines by region and found significant latitude-related correlations. This could explain why oysters are served with tabasco sauce and lemon in New Orleans, while New England clam chowder is rather bland.

The biologists did consider several alternative explanations for spice use and discounted all but one. The problem with the "eat-to-sweat" hypothesis -- that people in steamy places eat spicy food to cool down with perspiration-- is that not all spices make people sweat, Sherman says, "and there are better ways to cool down -- like moving into the shade. " The idea that people use spices to disguise the taste of spoiled food, he says, "ignores the health dangers of ingesting spoiled food." And people probably aren't eating spices for their nutritive value, the biologist says, because the same macronutrients are available in similar amounts in common vegetables, which are eaten in much greater quantities.

The micronutrient hypothesis -- that spices provide trace amounts of anti-oxidants or other chemicals to aid digestion -- could be true and still not exclude the antimicrobial explanation, Sherman says. However, this   hypothesis does not explain why people in hot climates need more micro-nutrients, he adds. The antimicrobial hypothesis does explain this.

Darwinian Gastronomy

"Eeating is definitely one of the more social behavior of "Homo sapiens"s,  and it's a good way to see the interaction between cultural evolution and biological function. I believe that recipes are a record of the history of the coevolutionary race between us and our parasites. The microbes are competing with us for the same food. Everything we do with food -- drying, cooking, smoking, salting or adding spices -- is an attempt to keep from being poisoned by our microscopic competitors. They're constantly mutating and evolving to stay ahead of us. One way we reduce food-borne illnesses is to add another spice to the recipe. Of course that makes the food taste different, and the people who learn to like the new taste are healthier for it," said Sherman.

The research appears in the March 1998 issue of the journal "Quarterly Review of Biology".

Top 30 Spices with Antimicrobial Properties
(Listed from greatest to least inhibition of food-spoilage bacteria)

1. Garlic
2. Onion
3. Allspice
4. Oregano
5. Thyme
6. Cinnamon
7. Tarragon
8. Cumin
9. Cloves
10. Lemon grass
11. Bay leaf
12. Capsicums
13. Rosemary
14. Marjoram
15. Mustard
16. Caraway
17. Mint
18. Sage
19. Fennel
20. Coriander
21. Dill
22. Nutmeg
23. Basil
24. Parsley
25. Cardamom
26. Pepper (white/black)
27. Ginger
28. Anise seed
29. Celery seed
30. Lemon/lime

Source:  "Antimicrobial Functions of Spices: Why Some Like It Hot," Jennifer Billing and Paul W. Sherman, "The Quarterly Review of Biology", Vol. 73, No.1, March 1998

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