Food Bacteria-Spice Survey Shows Why Some Cultures Like It Hot

ITHACA, N.Y. -- Fans of hot, spicy cuisine can thank nasty bacteria andother foodborne pathogens for the recipes that come -- not socoincidentally -- from countries with hot climates. Humans' use ofantimicrobial spices developed in parallel with food-spoilagemicroorganisms, Cornell University biologists have demonstrated in ainternational survey of spice use in cooking.

The same chemical compounds that protect the spiciest spice plants fromtheir natural enemies are at work today in foods from parts of the worldwhere -- before refrigeration -- food-spoilage microbes were an even moreserious threat to human health and survival than they are today, JenniferBilling and Paul W. Sherman report in the March 1998 issue of the journal"Quarterly Review of Biology".

"The proximate reason for spice use obviously is to enhance foodpalatability," says Sherman, an evolutionary biologist and professor ofneurobiology 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 certainflavors. People who enjoyed food with antibacterial spices probably werehealthier, especially in hot climates. They lived longer and left moreoffspring. And they taught their offspring and others: 'This is how tocook a mastodon.' We believe the ultimate reason for using spices is tokill food-borne bacteria and fungi."

Sherman credits Billing, a Cornell undergraduate student of biology at thetime of the research, with compiling many of the data required to make themicrobe-spice connection: More than 4,570 recipes from 93 cookbooksrepresenting traditional, meat-based cuisines of 36 countries; thetemperature and precipitation levels of each country; the horticulturalranges of 43 spice plants; and the antibacterial properties of each spice.

Garlic, onion, allspice and oregano, for example, were found to be the bestall-around bacteria killers (they kill everything), followed by thyme,cinnamon, tarragon and cumin (any of which kill up to 80 percent ofbacteria). Capsicums, including chilies and other hot peppers, are in themiddle of the antimicrobial pack (killing or inhibiting up to 75 percent ofbacteria), while pepper of the white or black variety inhibits 25 percentof bacteria, as do ginger, anise seed, celery seed and the juices of lemonsand limes.

The Cornell researchers report in the article, "Countries with hotterclimates used spices more frequently than countries with cooler climates.Indeed, in hot countries nearly every meat-based recipe calls for at leastone spice, and most include many spices, especially the potent spices,whereas in cooler counties substantial fractions of dishes are preparedwithout spices, or with just a few." As a result, the estimated fractionof food-spoilage bacteria inhibited by the spices in each recipe is greaterin hot than in cold climates.

Accordingly, countries like Thailand, the Philippines, India and Malaysiaare at the top of the hot climate-hot food list, while Sweden, Finland andNorway are at the bottom. The United States and China are somewhere in themiddle, although the Cornell researchers studied these two countries'cuisines by region and found significant latitude-related correlations.Which helps explain why crawfish etoufée is spicier than New England clamchowder.

The biologists did consider several alternative explanations for spice useand discounted all but one. The problem with the "eat-to-sweat" hypothesis-- that people in steamy places eat spicy food to cool down withperspiration -- 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, hesays, "ignores the health dangers of ingesting spoiled food." And peopleprobably aren't eating spices for their nutritive value, the biologistsays, because the same macronutrients are available in similar amounts incommon vegetables, which are eaten in much greater quantities.

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

The study of Darwinian gastronomy is a bit of a stretch for an evolutionarybiologist like Sherman, who normally focuses his research on the role ofnatural selection in animal social behavior and is best known for hisstudies of one of nature's most social (and unusual-looking) creatures, thenaked mole-rat ("Heterocephalus glaber") of Africa. But eating isdefinitely one of the more social behavior of "Homo sapiens"s, hemaintains, and it's a good way to see the interaction between culturalevolution and biological function. "I believe that recipes are a record ofthe history of the coevolutionary race between us and our parasites. Themicrobes are competing with us for the same food," Sherman says."Everything we do with food -- drying, cooking, smoking, salting or addingspices -- is an attempt to keep from being poisoned by our microscopiccompetitors. They're constantly mutating and evolving to stay ahead of us.One way we reduce food-borne illnesses is to add another spice to therecipe. Of course that makes the food taste different, and the people wholearn to like the new taste are healthier for it."

For biology student Billing, the spice research for a senior honors thesistook her to an unfamiliar field, food science, and to the CornellUniversity School of Hotel Administration, where the library contains oneof the world's largest collections of cookbooks. Now that thebacteria-spice connection is revealed, librarians everywhere may want tocross-index cookbooks under "food safety." And spice racks may startappearing in pharmacies.

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Top 30 Spices with Antimicrobial Properties

(Listed from greatest to least inhibition of food-spoilage bacteria)

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

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