by C. Rose Kennedy
figures by Kaitlyn Choi
What’s in a Flavor?
The word “flavor” pervades our daily vocabulary, evoking associations of rich or vivid experiences beyond the experience of eating. Even in the literal context, the Flavor Extract Manufacturers Association (FEMA) describes flavor as “the entire range of sensations that we perceive when we eat a food or drink a beverage. Flavor encompasses a substance’s taste, smell, and any physical traits we perceive” . While foods do intrinsically contain flavoring substances, 90% of Americans’ grocery purchases also contain added flavors . These flavors are used to amplify or modulate the sensory experience associated with existing qualities of a product. Furthermore, they may also be used to make healthy yet bland options (like those lacking an excess of sugar or trans-fats) more appealing. For example, flavor agents may make reduced-fat foods seem rich and creamy, or add salty zest to low-sodium products. It’s obvious that flavors have immense power to influence our gustatory experiences, but what are they and where do they come from?
All flavors, including those intrinsically present in food, as well as natural and artificial flavor additives, are small chemical compounds or mixtures of compounds (Figure 1). While chemicals often evoke negative associations, it’s important to remember that all of the components of our food, our bodies, and the world around us are actually chemicals. Even things like water (dihydrogen monoxide), table sugar (sucrose, or alpha-D-glucopyranosyl-(1à2)-beta-D-fructofuranoside), and baking soda (sodium bicarbonate) are chemical compounds. In fact, the chemical properties and structures of flavoring substances are exactly what enable them to react with each other during cooking (think of that distinctive grilled flavor) bind with the taste receptors in our mouths.
The FDA broadly defines natural flavors to include any flavor isolated from natural sources like plant material (fruits, roots, bark, herbs, etc.) or animal products (meat, dairy, etc.) . Artificial flavors are any flavors that are not defined as natural, even if they have the exact same chemical composition as flavors isolated directly from nature . This distinction between the origins of flavors has no bearing on how safe, healthy, or delicious they are. In fact, flavor agents produced in a controlled laboratory setting undergo rigorous quality control at every stage, and do not require a lengthy, labor- and resource-intensive extraction process or acquisition of naturally rare or difficult-to-cultivate materials. As such, many nature-identical artificial flavors are actually available in higher purity than their natural congeners and may be obtained with less damage to the environment .
These artificial flavors are prepared by an elite group of highly trained professionals known as flavorists or flavor chemists, who must proceed through a rigorous seven-year apprenticeship (following university education) before they can become certified by the Society of Flavor Chemists [5, 6]. It is estimated that there are only roughly 500 certified flavorists worldwide . Flavorists prepare mixtures of flavors to meet consumer flavor preferences, all while following a stringent set of safety and efficiency guidelines. Furthermore, because they are considered ingredient manufacturers flavorists and flavor production companies must comply with all the same FDA and USDA rules developed for food production .
To aid this process, a panel of scientific and medical experts (representing fields including chemistry, toxicology, pharmacology, medicine, pathology, and statistics) serving the Flavor Extract Manufacturers Association (FEMA) has compiled a list of thoroughly vetted flavor compounds that are “generally recognized as safe (GRAS)” . The FEMA Expert Panel communicates their findings and all scientific data with the FDA, with international scientific and regulatory bodies, and in the scientific literature [8, 9]. Flavor companies are not required to disclose application of flavor ingredients that have already passed this rigorous review, but any novel flavor substances that have not yet made it onto the list require rigorous testing and approval to demonstrate safety before they may be incorporated into consumer products.
Let’s consider a few cases of flavor chemistry in action!
Vanilla is the most popular flavor worldwide. Not only is it used in favorites like ice cream, candies, cakes, and cookies, but vanilla also enhances perception of sweetness and other flavors (like those in chocolate, coffee, fruit, and nuts) .
Natural vanilla extract is obtained by steeping vanilla beans in alcohol to afford a solution of vanillin and other minor components that may be used in cooking and baking. While as many as 250 taste and aroma components have been detected in vanilla extract, most of these are destroyed upon exposure to elevated temperature, causing the complexity of the vanilla flavor to diminish upon baking. Furthermore, vanilla beans can only be obtained from hand-pollinated flowering orchids in a handful of tropical areas, making them precious commodities, especially given the vast demand for vanilla (over 16,000 metric tons annually) worldwide . To meet this demand, flavor companies like International Flavors and Fragrances, Inc. and Givaudan have entire production lines devoted to development of high-quality substitutes for natural vanilla extract , .
One of these substitutes is castoreum extract. Castoreum is a secretion from the anal glands and castor sacs of beavers, which use it to mark their territorial claims. Castoreum extract possesses a warm, sweet odor and may be used as a stand-in for vanilla extract in many dairy products and baked goods . Following rigorous evaluation, castoreum and its extracts have earned a place on the GRAS List; however, worldwide consumption is relatively low (only about 300 pounds annually). It is interesting to note, though, that because castoreum is extracted from an animal source, it is considered a natural flavor, not an artificial flavor.
The bulk of vanilla substitutes are actually nature-identical vanillin and vanillin derivatives synthesized on multi-ton scale from guaiacol or lignin extracts, which can be isolated from wood pulp (Figure 2) , . In addition to providing an inexpensive source of vanillin—in higher purity than one could obtain from natural vanilla extract—this synthesis enables production of vanillin derivatives possessing desirable qualities, like increased flavor potency and thermal stability. For example adding one extra carbon atom to vanillin affords ethyl vanillin, which is 2–4 times more flavorful than vanillin itself. Due to this desirable property and its long-standing status on the GRAS list, ethyl vanillin has been used in some vanilla flavoring since the 1930s.  Perhaps it should come as no surprise, then, that in blind taste-tests, tasters preferred the artificial vanilla flavoring (including industrially produced vanillin and its analogues) in treats like cookies that must be baked at the high temperatures that cause many of the minor components of natural vanilla extract to decompose .
Butter Me Up
The rich, smooth flavor of butter is another consumer favorite, adding body and depth to cooking sprays, sauces, baked goods, and (of course) popcorn. This flavor arises from the production of diacetyl and acetoin as byproducts of sugar fermentation in the production of cultured dairy products like cultured butter, buttermilk, and sour cream .
While small quantities of these compounds can be isolated from these consumer-based dairy products, the very low efficiency of the extraction limits its practicality. Instead, these flavor additives are generally produced through chemical synthesis or industrial fermentation on specialized culture, which is optimized for flavor production, but is not the sort of media people generally like to eat (Figure 3) . When produced through this culturing technique, diacetyl and acetoin are listed as “natural butter flavoring,” but when they are produced through controlled laboratory synthesis, the very same components are listed as “artificial butter flavoring” .
You may have heard reports about “popcorn worker’s lung,” in which a handful of cases of lung disease have been linked to inhalation of very high levels of diacetyl in some microwave popcorn production facilities . However, both diacetyl and acetoin are long-standing members of the GRAS list. It is essential to remember that a high dose of anything can be toxic! For example, there have been numerous cases of deaths related to overdosing on water (not drowning, actually just drinking far too much) , . The FDA and OSHA have investigated concerns regarding aerosolized diacetyl carefully and have developed new standards to limit exposure to airborne particles in occupational settings . Additionally, their reports reiterate that the levels to which general consumers are exposed is far below the risk threshold. Furthermore, ingesting flavor agents like diacetyl routes these substances to the stomach (rather than the lungs), which is perfectly equipped to process these molecules. So go ahead, have your butter (flavor) and eat it too!
A Flavor Like You’ve Never Dreamed
As a few of our classic flavor favorites illustrate, flavor chemistry is both an art and a science dedicated to safely producing robust and resource-efficient natural and artificial flavors for your enjoyment. Perhaps the most exciting aspect, however, is the opportunity to combine known flavors in novel ways to explore flavors beyond what we’ve ever experienced. Flavorists seek to identify and fill “white spaces,” which are combinations of flavor qualities that consumer may enjoy but are unrepresented in products on the market. So next time you try an out-of-this-world treat like Juicy Fruit™ gum, a novel jelly bean, or your favorite sports drink, remember the labor of love that went into its development . For in the memorable words of Willy Wonka: “Invention, my dear friends, is 93% perspiration, 6% electricity, 4% evaporation, and 2% butterscotch ripple.”
C. Rose Kennedy is a Ph.D. candidate in the Department of Chemistry and Chemical Biology at Harvard University.
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