Packing a Punch with Pungency

Packing a Punch
with Pungency
September 1998 -- Applications

By: Kimberly J. Decker
Contributing Editor

    Anyone who has experienced the cooling effect of a menthol drop or the sinus-clearing punch of too much hot-pepper sauce knows that traditional tastes and flavors aren't the only factors contributing to a food's character. Indeed, many of the foods we enjoy - such as chile pepper, horseradish, mint and ginger - would not have nearly so much appeal were it not for their pungency. The bottom line: pungency is popular.Irritation  The term "pungency" encompasses several sensations in foods, ranging from the bite of mustard or the burn of a pepper, to a mint's cooling action and tequila's alcoholic sharpness. These sensations all result from the action of food chemicals on what is known as the trigeminal nerve; the sensations themselves comprise the trigeminal sense. Although it isn't entirely understood how these chemicals act on the nerves to initiate trigeminal responses, the overwhelming global preference for pungent foods has spawned increased research into the workings of the trigeminal sense.  Basically, the trigeminal sense resembles taste and smell in that it is recognized as an individual sensory system. But it stands apart from those more common chemical senses in several ways. "The definition we have for tastes is that they go through a specific nerve," says Jean-Marc Dessirier, sensory researcher, University of California-Davis. "Now, the other sensation that we have in the mouth, including the sensation of what I call spiciness, goes through a different set of nerves." This set of nerves is the trigeminal, whose three main branches enervate the eyes, the oral and nasal mucosa, and, to some degree, the facial skin. This path of enervation explains why a hot bowl of chile can burn your mouth and lips, and open the floodgates in your eyes and nose. But because of the difference in which nerves are stimulated, Dessirier says that spiciness is "a different sensation; it's not a taste, although it is often called a hot 'taste.' It's not a smell either." Essentially, it is the trigeminal sensation we call pungency.  Although the trigeminal nerve resembles the major taste and smell nerves by having chemoreceptors sensitive to certain food chemicals, it distinguishes itself from the common chemical senses by having a variety of other unique receptors. These include mechanoreceptors that respond to tactile sensations, thermoreceptors that are sensitive to changes in temperature, proprioceptors that register to motion, and nociceptors that mediate pain responses. So, to put the pieces together, the trigeminal receptors in the facial area respond to irritants in foods in such a way that leaves us with sensations ranging from mildly tingly to downright agonizing. It's that simple, right?  Well, not quite. "It's an absolutely huge field," says Bruce Bryant, Ph.D., senior research associate, Monell Chemical Senses Center, Philadelphia. And it is an area upon which science is only beginning to cast a clear light. "The evolutionary purpose for the trigeminal sense is to really warn an organism that it's about ready to be hurt or that it's already hurt," Bryant explains. This does not mean that foods we perceive as spicy put us in any danger when we eat them. Although some theories suggest that the runny nose and crying that characterize the trigeminal response are ways of expelling harmful substances from the body, all common pungent foods are considered GRAS. Instead, these foods initiate a trigeminal response for a number of different reasons. "The fact that foods are pungent has more to do with the fact that plants are taking advantage of a sensitivity in the organisms that eat them," Bryant says. "Plants can elaborate compounds so they have defenses against being eaten."  Trigeminal chemoreceptors and nociceptors aside, common knowledge says that certain irritating chemicals in foods cause the sometimes painful sensation known as pungency. The capsaicin found in chiles, the pipperine in black pepper, ginger's gingerols, and the biting isothiocyanates found in mustard and horseradish are some of the more obviously pungent compounds. It might be more surprising to learn that the cooling effect of menthol in mint oil is really just a different form and strength of that same pungency. In other words, both minty refreshment and peppery heat result from the same sensory stimulation and thus lie on different ends of the very same sensory continuum.Hot, but not  With all due respect to cool mint, people usually describe the overwhelming sensation experienced when eating something pungent - such as a chile pepper or horseradish - as "hot." But those foods are not necessarily hot in terms of temperature. The trigeminal nociceptors and thermoreceptors simply jumble the sensation in such a way that our brains confuse the pungent sensation with heat. "Within the nociceptors, there are also a wide range of different fibers that respond to different types of things," Dessirier says. And sensory scientists do not know which specific fibers respond to one stimulus and not another. "What we think is that the fibers that are actually stimulated by chemical irritants - the spicy compounds - are called 'polymodal' nociceptors, because they respond to different kinds of painful stimuli, including mechanical pain, which would be the equivalent of pinching; thermal pain, which is either very hot or cold, but is usually very hot; and chemical pain," which comes from contact with the irritant compounds in foods like hot pepper. So, people just sense this chemically stimulated "heat" as thermal heat.  Another reason for attributing a spicy food's impact to heat might be that the food stimulates both the heat- and pain-sensing fibers, Dessirier says. Recent evidence hints that receptors for capsaicin, the irritant in chile peppers, are similar to trigeminal thermoreceptors. The physiological mode that capsaicin uses to act on trigeminal nerves involves its interaction with a recently recognized ion channel, according to Bryant. "It's a nonspecific cation channel that lets a lot of calcium and sodium into the neurons," he explains. And if the same channels react to both nociceptor and thermoreceptor stimulation, it could explain the essentially false perception of heat in a "hot" pepper.Hot times  Pungency has risen in popularity: A growing ethnic population and rising ethnic dining trend has helped the United States double its per capita fresh-chile consumption from 3.3 lbs. in 1980 to 6.5 lbs. in 1996. This has led not only to more research into trigeminal physiology, but exploration into pungency's chemistry as well.  Of all the "heat"-producing compounds, the capsaicinoids - the pungent principles in the Capsicum species of chile peppers - have probably received the most interest. Five major classes of capsaicinoids exist, all vanillylamides of monocarboxylic acids. Capsaicin and dihydrocapsaicin are the most common capsaicinoids and contribute the most heat to peppers, where they are concentrated in the white veins and seeds.  Our ability to perceive a pepper's heat depends on the ability of its capsaicin to make contact with trigeminal nerve endings. That, in turn, depends on capsaicin's solubility. "Capsaicin is an oil-soluble compound that readily gets through the skin," Bryant says, "though it does have a barrier on the tongue to get through." The tongue is not too formidable a barrier however, since capsaicin's oil solubility makes for easier transmission through the lipid membranes of the cells in the oral mucosa.  As an oil-soluble molecule, its entry into the trigeminal system and its effects differ from those of volatile irritants like isothiocyanates in horseradish. "The difference between capsaicin and horseradish is really a matter of access," Bryant explains. The irritants in the latter, being volatile, have greater access to the sensory mucosa in the nasal passages, where the nerve endings are relatively close to the surface. This permits a quicker and fuller release of the volatiles into the nasal mucosa than onto the tongue. Volatility brings the first punch of horseradish's pungency to the back of the palate and the nasal passages, while capsaicin's association with the solid phase locates its earliest bite more directly on the tongue and the skin of the mouth itself.Measuring up  Depending on the variety of pepper, where it was grown, and how mature it was at harvest, capsaicinoid content in chiles can vary widely. While common red peppers contain, on average, about 0.06% capsaicinoids, African varieties can have up to 0.85%. Because of this variation in fieriness, food processors and chile fans needed a more descriptive and accurate way of rating a pepper's burn levels than the terms "mild, medium and ouch!"  Obtaining an organoleptic measure of a chile's heat involves performing the Scoville heat test. This sensory system uses trained panelists to taste increasingly concentrated dilutions of pepper to identify the lowest concentration at which they detect the characteristic capsaicin burn. The reciprocal of that dilution is taken as the Scoville heat unit for that pepper. To ensure accurate and objective results, panelists must be careful not to cause their palates to fatigue - a tough task when dealing with peppers' irritating nature.  Fortunately, HPLC, which measures capsaicinoids in parts per million, can back up the more subjective sensory method. But while HPLC can give an exact, quantitative measure of capsaicinoid content for a particular chile pod, like the sensory method, it says nothing about other pods from different locations or different climatic conditions. For a more comprehensive picture of a pepper's heat, the percent capsaicinoids, as determined by HPLC, can be mathematically correlated to sensory Scoville heat units. Stuart Jeffery, president, Quetzal Foods International Corporation, New Orleans, says "sensory and HPLC Scoville testing are day and night factors, and within each of these standards and each group of people - the sensory testers and HPLC lab - there are variances." His experience has been that the "right" testing lab - whether using sensory or instrumental methods - is essential.Spicing up your life  The heat index is not the only consideration for processors wanting to take advantage of peppers' appeal. "The capsicum species is not just hot," Jeffery says. "It is also flavorful, colorful, aromatic, and texturizing, all of which influence the mouthfeel and total sensory perception of any recipe." The best route for product designers is to experiment with different kinds of chiles, he recommends. The number and variety commercially available today - from the smoky chipotle to the sweeter, milder poblano - practically guarantee a good flavor match. But it is important to establish a "relationship" with the chiles themselves. Get to know which ones have more flavor than others by tasting them; become familiar with the location in the mouth where a pepper creates a burn and whether it dissipates or lingers; and take into consideration the differing textures among the dried and fresh varieties.  Often, the best chile to use is actually a mixture. "Each ingredient adds its own qualities to the recipe," Jeffery says. "Therefore, it is very important, when experimenting with chile combinations, that each chile is sensed separately within the recipe prior to the next being added." Indeed, some have relatively weak tastes and heat levels, a characteristic that may make them just fine on their own, but can render them inadequate when paired against more powerful varieties. As a remedy for a chile that "falls off," consider using a larger quantity to stretch the pepper's heating and flavoring effects.  And while a carefully selected and proportioned blend of chiles can add significant flavor, texture and overall sensory appeal to a formulation, it is certainly possible to go overboard and create a product that is devastatingly hot. When the heat of a chile overpowers even the strongest ingredients, the brain and mouth can no longer distinguish the recipe's real purpose. Most consumers do not want an isolated experience of pure heat, but rather wish to notice the threshold levels for each ingredient in a product that exhibits sensory variety.  The key to keeping powerful peppers in check is to determine which chiles are actually attainable and then to decide what heat and flavor specifications are appropriate for the application. Once that is done, formulators should: combine chiles of different strengths and flavor levels; look for milder samples of the same varietal; reduce the amount of the overpowering ingredient; and use trial and error. Jeffery encourages developers to use notoriously hot peppers, but to use them wisely.The real thing?  Beyond the question of how much or what kind of chile to use in a recipe lies the debate over using chile oleoresins (the extracted essential oils) or the actual chile itself. Jeffery believes the former isn't the best choice if achieving real chile flavor is the goal. In some extractions, it is often only the heat that comes through. But among the benefits of extractions are their precise heat and flavor levels, and their relative imperviousness to growing conditions. "With natural chiles, every factor, from the seed to the storage of the delivered product, affects everything." But despite threats, such as microbiological contamination and oxidation, Jeffery recommends using the natural chile, believing that the different interactions often give the pepper a desirable heat and flavor profile unattainable with an extraction.  For chile extracts, plenty of delivery-system options exist. Dried flavoring powders and chile sauces are common, and oleoresins can pack a lot of pungency into an oil-soluble form. But water-soluble and spray-dried forms of chiles are becoming more popular. And since some interactions between chile flavors and the food matrix can detrimentally affect both, new methods of encapsulating chile flavors have been developed, leading to increased flavor stability and shelf life. Mane USA, Wayne, NJ, has been conducting work in flavor-encapsulation using beta-cyclodextrin. A donut-shaped molecule that traps flavors based on their solubility and polarity, beta-cyclodextrin protects them from the food environment (and the environment from them) until the appropriate time for flavor delivery - either during manufacturing or in the consumer's home. The line of natural Mexican chile flavors developed by McCormick Flavors, Hunt Valley, MD, also offers four of its chile flavors in two different encapsulated forms.Chilling out  Opposite capsaicin's heat on the trigeminal spectrum lies the cooling sensation of peppermint, spearmint and wintergreen. This sensation occurs when compounds in these flavors interact with trigeminal cooling receptors in the nasal or oral tissues. Menthol (in its natural, l-isomer form), is responsible for most of mint's cooling character. And though the crystalline form of some polyols, such as xylitol, create a slight cooling feeling from their endothermic breakdown, this differs from a menthol cooling sensation.  Menthol bears the distinction of being both volatile and oil-soluble, which allows it to enter the nasal passages with enough left in the solid or liquid phase to pass through the epithelium of the tongue and mouth. There it basically resets thermal receptors, sensitizing them to cooling. This cooling depends heavily on evaporation. "If you put some menthol in your mouth and close your mouth," Bryant says, "there's not too much of a thermal, cool sensation." Just breathe in, however, and the evaporation helps intensify the effect.  But cooling is not the only effect menthol has - depending on its concentration, menthol can be cooling or irritating. While lower concentrations seem to stimulate the trigeminal cold fibers, the irritating sensation occurs when higher concentrations interact with nociceptors. "There might be a cross-connection somewhere, but we really don't know about that," Dessirier says. This irritation isn't really as uncommon as it might initially seem: Just brush your teeth or gargle with a large amount of minty toothpaste or mouthwash, and then feel your eyes start to water and your mouth burn. Dessirier also points out that drinking cold water after using a mentholated product can result in a mildly stinging sensation as well. "That's because some of the cold fibers, having been stimulated by menthol, instead of coding the water's temperature as just cold, push it into the pain range."Making mint work  Menthol can be effectively used in products where a cooling sensation is desirable: candies, lozenges, some beverages and certain baked goods. Given the number of mint flavors from which to choose, it helps to know what sets one apart from the other. "Spearmint and peppermint are a world apart," says Paulette Lanzoff, director of flavor creation and application, Mane USA. "Peppermint is very cool, the chief components being menthol, menthol acetate, menthone and terpenes." The predominance of menthol in peppermint gives it its characteristic chill. "Spearmint has a moderate amount of menthol, but the chief component in spearmint is levo-carvone, which is not really cool. It's more of a warming sensation." Carvone's high volatility brings it up into the nasal passages, making it a strong contributor to spearmint's aroma. Furthermore, even within a type of mint, there are multiple subspecies and varieties, each with its own flavor profile. Which variety a developer chooses to use is, as is the case with hot peppers, really a matter of aesthetics and a willingness to meet consumers' preferences.  As to the relative benefits of synthetic and natural mint flavors, Lanzoff admits that this decision is tough to make. Mint's major trigeminal-active component is indeed levo-menthol, and whether flavorists crystallize it from mint oil or synthetically produce it, it performs essentially the same way. The differences appear when mint oils themselves are compared. Based on the mint species, where it grows, and the season, the oil's characteristics can vary widely. This can have a profound effect on the quality of oils extracted from the plant. "There are compositional differences that can be analyzed and determined," Lanzoff says, "and then there's subtle flavor differences...for which the sensory ability is even more acute."  When choosing between menthol extracted from the plant's own oils and synthetic menthol, formulators should consider price in addition to quality. In comparison to menthol synthesized from petroleum byproducts, naturally extracted mint oil can cost up to 30 times as much.Special delivery  Mint flavors are popular in such a wide array of applications that finding the right delivery systems can be a bit tricky. The delivery system for a baked good should be weaker, Lanzoff says, ensuring equal mixing of the mint flavor with the rest of the ingredients. An emulsion could come in handy in this application to prevent any solvents from coming into direct contact with volatile solvents in the production facility. But for something like a hard candy or a lozenge, straight mint oil or mint-oil combinations (without solvents) can work well. Teas, a common application for mint, provide the option of employing dried mint leaves. For a flavor essence, Lanzoff says there are limited applications for liquid flavors using solvents, like ethyl alcohol, that can be plated onto the leaves and then evaporated off. However, most teas and other drink blends use dry flavors.  Another issue to consider is the duration of the flavor and cooling sensation. The general consensus is that the flavor essences last longer. "It's going to be stronger in concentration than the straight leaves, and there's less dependency on the consumer's extraction method to get the flavor delivered," Lanzoff explains. "So there's more standardization from usage to usage."  Regardless of the delivery system used, the strength of mint's lingering flavors and aromas can prove problematic in processing. "We find a lot of processors staying away from mint because they're afraid of cross-contamination in their plant," Lanzoff says.A new kind of cool  Just as chile pepper's bite differs from that of horseradish, not all cooling effects are identical, either. The difference between polyol sweeteners and menthol offers one example. At Mane USA, researchers have created Physcool™, a salt resulting from the combination of succinic acid and menthol, that offers a unique cooling sensation to products without introducing any mint flavor. Whereas menthol's cooling is very upfront and felt strongly in the nasal passages, this flavor sends the cooling into the back of the mouth and throat. This delays the release of the cooling effect and gives a sustained cooling perception at any temperature.  Besides enhancing existing mint flavors in such products as candies, lozenges and some pharmaceuticals, it also is ideal for such applications as sports beverages, where the predominant flavor is not mint, but where a cooling sensation is desirable even at room temperature and above. As a flavor potentiator, it helps avoid some of the problems associated with an excess of mint flavor. "An excess of menthol will create bitterness," Lanzoff says. "You may want to get more cool than you can get from menthol, without the bitterness."  Other, less obvious applications for the product include alcoholic beverages, where its cooling action makes the beverage seem more refreshing and enhances the perception of proof - making it attractive to producers of low-proof and no-proof beers. Researchers had been experimenting with the compound in chocolate and in hot-pepper sauces, where they expected it to create a hot-and-cold effect. "But what it did," Lanzoff says, "was it almost changed the way the heat is perceived in the mouth. It's a little difficult to describe."  With all the resources available, food product designers should have no problem creating a refreshing or zingy edge in a product. And given the popularity of the different manifestations of pungency, it seems as if any product could benefit from that edge.Ouch!
Fiery Foods Heat Scale Scoville Heat Units Chile Varieties/ Commercial Products 100,000 to 500,000 habanero Scotch bonnet, South American chinenses, African birdseye 50,000 to 100,000 santaka, chiltepin, rocoto Chinese kwangsi 30,000 to 50,000 piquin, cayenne long tabasco, Thai prik khee nu, Pakistan dundicut 15,000 to 30,000 de arbol crushed red pepper, habanero hot sauce 5,000 to 15,000 early jalapeÒo amarillo, serrano, TabascoÆ sauce 2,500 to 5,000 mild jalapeÒo, mirasol, cayenne large red thick Louisiana hot sauce 1,500 to 2,500 sandia, cascabel yellow wax hot 1,000 to 1,500 ancho, pasilla EspaÒola improved, Old Bay seasoning 500 to 1,000 NuMex Big Jim chile, NuMex 6-4 chile chili powder 100 to 500 NuMex R?Naky chile, Mexi-Bell, cherry, canned green chiles Hungarian hot paprika 10 to 100 pickled pepperoncini   0 mild bells, pimiento, sweet banana U.S. paprika
Courtesy of Quetzal Foods International Corporation.  Kimberly Decker, a California-based technical writer, has a bachelor's degree in consumer food science with a minor in English from the University of California-Davis. She lives in the San Francisco Bay Area, and enjoys cooking and eating food in addition to writing about it.Back to top