The procurement of spices was a motivating force throughout much of early history. The Gothic leader Alarich conquered the city of Rome in 408 AD. His ransom for relinquishing control of Rome was set at 5,000 pounds of gold and 3,000 pounds of pepper. The voyages of Pedro Cabral, Christopher Columbus, Hernando Cortez, Vasco da Gama, Ferdinand Magellan, Marco Polo and other explorers were made in the hopes of discovering quicker routes to spice-bearing countries (Sherman & Billing, 1998).

K. T. Farrell defines spices as "any dried, fragrant, aromatic, or pungent vegetable or plant substance, in the whole, broken, or ground form, that contributes flavor, whose primary function in food is seasoning rather than nutrition, and that may contribute relish or piquancy to foods or beverages" (Sherman & Billing, 1998). Why was such an economic emphasis placed on seemingly frivolous spices? Spices must somehow contribute more than just the obvious; this question has received much attention in recent years and has generated many hypotheses. One proposed hypothesis is that spices are used to mask the unpalatable taste and smell of spoiled foods. While spicing spoiled food would cover up the smell and taste, such a practice would not be beneficial (Sherman & Billing, 1999). Humans have evolved to be repulsed by the odor of spoiled foods as a defense mechanism to prevent ingestion of substances likely to cause botulism, food poisoning, or disease. Cultures that would chose to ignore this developed mechanism by using spices would be at a disadvantage, causing their civilization to be less than successful at extending their lineage.

It has been hypothesized that spices act as medicinal treatments, since many primitive societies use spices as pharmaceuticals (Sherman & Flaxman, 2001). Spices have been prescribed for aiding digestion, raising sexual potency, decreasing blood pressure, controlling metabolism, and delaying the onset of degenerative diseases (Sherman & Billing, 1999; Sherman & Hash, 2001). However, Sherman and Flaxman (2001) suggest that if the role of spices was to cure, then they would often be taken in much larger doses and added to nearly all dishes, not just dishes prepared for the ill. Spices taken for the purpose of treating an ailment would most likely be taken in larger doses than they are called for in most recipes.

Sherman and Billing (1999) considered that spices could be used to aid in cooling the individual by promoting perspiration. Although the ingestion of horseradishes and chilies cause sweating in some people, the majority of spices do not possess this effect (Sherman & Billing, 1999). It does not make sense from an evolutionary perspective for an individual desiring to cool him or herself to become active and search the land for spices. Natural selection would not permit such a poor compromise. Our bodies’ natural homeostasis mechanisms are much more effective and efficient at controlling body temperature.

Sherman and Billing (1999) also present the possibility that spices could have been used as a sign of wealth. Since acquiring spices in earlier days was not a simple task of going to the grocery store, only the affluent would be capable of enjoying them. Like any rarity, spices could be viewed as a sign of wealth, separating those with money from those without. This hypothesis is not supported by the fact that the rarest spices tend to be used in the tropics, generally considered as poor by many standards (Sherman & Billing, 1999).

One hypothesis remains that has been supported by numerous recent studies and provides adequate proximate and evolutionary explanations. In 1998, Paul Sherman and Jennifer Billing from Cornell University published a paper explaining and supporting this hypothesis. Sherman and Billing (1998) suggest that spices have an antimicrobial effect that acts as a natural preservative in foods. Their hypothesis must fulfill five predictions: 1) spices must have antimicrobial properties, 2) the use of spices must directly relate to temperature, 3) common spices must inhibit native bacteria particularly well, 4) in general, meat recipes should be spicier that vegetable recipes, and 5) within countries, spice use should increase with temperature.

Sherman and Billing (1998) conducted a study analyzing the use of 43 spices in 36 countries worldwide. A total of 4,578 meat-based recipes from 93 traditional cookbooks were involved in this study. The study was restricted to meat-based recipes because meat is more likely to spoil and cause food poisoning than plant products. The spices’ inhibitory effects were tested on 30 species of bacteria. Every spice included in Sherman and Billing’s study displayed inhibitory properties on at least one species of bacteria. Eighty percent of the spices tested inhibited 50 percent of the bacteria, and four spices, garlic, onion, allspice, and oregano, inhibited the growth of every species of bacteria in this experiment.

Additional studies on spices have yielded similar results. A study released by Ross, O’Gara, Hill, Sleitholme, & Maslin (2001) analyzed the antimicrobial properties of garlic products. The compound found to be responsible for inhibition of antimicrobials was allicin (allyl 2-propene thiosulfinate). Unique to this study was the discovery that allicin is not present in garlic cloves; instead, allicin is formed by the crushing of the garlic clove. This discovery explains the antimicrobial abilities of garlic powder and garlic oil. Garlic oil and garlic powder have displayed the ability to inhibit H. pylori, S. aureus and E. coli (Ross et al., 2001). Basil, cumin, caraway, and coriander have been proven to inhibit the growth of Aeromonas hydrophila, Pseudomonas fluorescence, and Staphylococcus aureus (Brul & Coote, 1999).

A study by De, De, and Banerjee (1999) tested the antimicrobial effects of 35 Indian spices on a gram-positive organism, a gram-negative organism, and yeast. The 35 spices where individually mixed into molten agar media at three concentrations. The organisms were then added to the solidified media and their growth was compared with a control group. The results indicated that 20 of the spices had antimicrobial properties. Of the 20 spices with antimicrobial properties, six spices had both antibacterial and antifungal properties.

These results do not come as a surprise. Spices are evolved chemicals produced by plants as a means of defense against their natural predators. This defense can deter insects from eating the plant by giving off a pungent taste and aroma. This defense can also protect the plant from microscopic predators by inhibiting the growth of bacteria and fungi within the plant. Humans, to inhibit microbial growth, add these same chemicals that are used by plants, for preserving food (Sherman & Hash, 2001). Many scientists have suggested that the antimicrobial effects of spices might be removed by exposing the spice to heat during cooking. K.E. Diebel and G. J. Banawart explored this possibility by running a test in which oregano, sage, and ground cloves were heated at 42 degrees Celsius. It was found that after 16 hours of heating, all three spices still inhibited the growth of Campylobactor jejuni, a common cause of gastroenteritis.

The second prediction in Sherman and Billing’s (1998) hypothesis is that spices should be used most frequently in the hottest climates. High temperatures expedite food spoilage; therefore if spices were originally used to prevent food spoilage, they should be used most frequently near the equator. The results of Sherman and Billing’s study supported this prediction. Many of the spices that are commonly called for in warm-climate countries are used in 40 percent or more of the recipes. The most commonly used spices in colder countries are called for in less than five percent of the recipes. These results give validity to the idea that spices were initially used as preservatives. Cultures in cool climates would not need the antimicrobial effects of spices to prevent food spoilage as much as people in hot climates. Hot-climate cultures often utilize specific spices, those most effective at warding off bacteria. Cold-climate cultures had the privilege of selecting their spices more freely, because only a small inhibitory effect was necessary.

Sherman and Billing (1998) found an increase in average annual temperature to be directly correlated to an increase in the number of recipes that list at least one spice in the ingredients. The results also showed a direct correlation between increasing average annual temperature and the average number of spices called for in a recipe. As the average annual temperature increased so did the average proportion of recipes that require highly potent spices. For the purpose of this study, a spice was considered highly potent if it inhibits the growth of 75 percent of the bacteria the spice was tested against.

The third prediction of Sherman and Billing’s antimicrobial hypothesis is that spices commonly used in a country should be particularly potent at inhibiting bacteria that are native to the area. Sherman and Billing (1998) could not obtain data to support or contradict this prediction. With data from the World Health Organization, the two researchers were able to assemble lists of indigenous bacteria for nine countries. Out of these nine countries, only five were represented with cookbooks in the study. A look at cases of food poisoning in Korea and Japan reveals indirect support for this third prediction. From 1971 to 1990, 29.2 out of 100,000 Japanese citizens were victims of food poisoning. In Korea, a nearby country with a similar climate to Japan, only 3.0 out of every 100,000 citizens experienced food poisoning. This difference was thought to be attributed to differences in food preparation and handling. Upon analyzing the use of spices in these countries, there is a correlation between few cases of food poisoning and heavy use of spices. Korean recipes call for the use of 3.6 spices per recipe as opposed to Japan’s use of 2.2. The average Korean dish was determined to inhibit the growth of 51 percent of food-born bacteria while the average Japanese dish inhibited only 12 percent.

The fourth prediction of Sherman and Billing’s hypothesis is that meat recipes should be spicier than vegetable recipes. Plant cells are better protected from bacteria and fungi after death than animal cells. Plant cells have the advantage of a cellulose and lignin cell wall and an internal acidic pH of 4.3-6.5. The cell membranes of animal cells do not offer efficient protection from invasion following death. The cell’s neutral pH of 6.6-7.5 provides an ideal medium for bacteria growth (Sherman & Hash, 2001). In 2001, Paul Sherman teamed with Geoffrey Hash to conduct a study on vegetable recipes similar to Sherman and Billing’s meat-recipe study in 1998. The results of the study studies showed that vegetable recipes call for 2.4 spices on average, 1.5 fewer than the average meat recipes. In 27 of 34 countries, there were more vegetable recipes that called for zero spices than meat recipes calling for zero spices. The ratio of recipes calling for more than one of the 15 most potent spices was greater in meat recipes than for vegetable recipes.

The last piece to the antimicrobial hypothesis is that spice use should increase proportionally within a country as temperature increases. To find data for this hypothesis, Sherman and Billing (1998) gathered regional traditional cookbooks from China and the United States. The results were supportive of the prediction; as average annual temperature increased, so did the proportion of potent spices used.

The hypothesis of Sherman and Billing provides a structure that matches the proximate data and evolutionary principles. In a time before refrigeration and modern preservation techniques, all foods, meat in particular, spoiled very easily in warm climates. Tribes that relied on finding food when they were hungry or always ate their findings immediately following their discovery would constantly risk their well-being. If the food was not preserved and eaten after setting for a few hours, the intended nourishment could have turned into a bacteria cocktail causing illness and possibly death. An unsuccessful week of hunting and gathering could result in the death of the tribe. With the death of the tribe, the tradition of finding food upon necessity would go "instinct". This unsafe practice would cause the tribe to be unfit in an evolutionary perspective and their techniques would be selected against. A tribe that employed the use of spices could gather and prepare foods in advance. The spiced food that remained a day or two after it was prepared could still be safely ingested. These people would fare better in times of unsuccessful hunts. In addition, these people would not have to worry about eating food that may have been left over and spoiled from the previous day.

Nielsen and Rios (2000) explored the possibilities of using spices to preserve foods through the process of active packaging, preserving the food by controlling the sealed atmosphere of the package. Active packaging in the past has consisted of placed oxygen-absorbing agents in contact with or within the package of food. Nielsen and Rios tested the effects of mustard oil in active packaging of hot dog buns and rye bread. The mustard oil was tested as a fungi inhibitor and the minimal concentration of mustard oil required to obtain a reasonable shelf life was determined. These concentrations were then added in the packaging process of hot dog buns and rye bread. It was determined that the amount of mustard oil needed to inhibit fungal growth effected the taste of the hot dog buns. The same amount of mustard seed oil went undetected in the packaging of rye bread.

O. Peter Snyder (1997) at the Hospitality Institute of Technology and Management has released a list of spices with a known inhibitory effect against specific microbials. His list includes cinnamon, cloves, and mustard as strong inhibitors; allspice, bay leaf, caraway, coriander, cumin, oregano, rosemary, sage, and thyme as medium inhibitors; black pepper, red pepper, and ginger as weak inhibitors. While he encourages the use of these spices, he also warns that spice use should not displace conventional methods of preservation. Causes of food poisoning have been traced back to contaminated fresh spices improperly cleaned before use and grown in poor conditions.

From the above evidence, it is clear that spices have great potential as preservatives in a society that prides natural ingredients. Sherman and Billing’s work appears as the most optimistic view of spices, where many common spices have outstanding antimicrobial effects. On the other hand, Snyder’s article warns the reader that food poisoning can result from the use of contaminated spices. It is obvious that more work is necessary to determine the practicality of spices as preservatives. Regardless of their antimicrobial effects, Cajun and other spicy dishes will continue to be served throughout the warmer climates. Why? Simply because spices taste good.

Brul, S., & Coote, P. (1999). Preservative agents in foods: Mode of action and microbial resistance mechanisms. International Journal of Food Microbiology, 50, 1-17.

De, M., De, A. K., & Banerjee, A. B. (1999). Antimicrobial screening of some Indian Spices. Phytotherapy Research, 13, 616-618.

Nielsen, P. V., & Rios, R. (2000). Inhibition of fungal growth on bread by volatile components from spices and herbs, and possible application in active packaging, with special emphasis on mustard essential oil. International Journal of Food Microbiology, 60, 219-229.

Ross, Z. M., O’Gara, E. A., Hill, D.J., Sleightholme, H. V., & Maslin, D.J. (2001). Antimicrobial properties of garlic oil against human enteric bacteria: Evaluation of methodologies and comparisons with garlic oil sulfides and garlic powder. Applied and Environmental Microbiology, 67(1), 475-480.

Sherman, W. P., & Billing, J. (1998). Antimicrobial functions of spices: why some like it hot. Quarterly Review of Biology, 73(3), 1-47.

Sherman, W. P., & Billing, J. (1999). Darwinian gastronomy: Why we use spices. Bioscience, 49(6), 453.

Sherman, W. P., & Flaxman, S. M. (2001). Protecting ourselves from food. American Scientist, 89(2), 142.

Sherman, W. P., & Hash, G. A. (2001). Why vegetable recipes are not very spicy. Evolution and Human Behavior, 22, 147-163.

Snyder, O. P. (1997, August 12). Antimicrobial effects of spices and herbs. Retail Food System Reports. Retrieved November 4, 2001 from the World Wide Web: http://www.hi-tm.com/Documents/Spices.html