New Frontiers in Flavor Interactions

By Jeanne Turner
Contributing Editor

Any dinner-party guest choking their way politely through a less-than-delightful dish would have plenty to say about adverse flavor reactions. However, while a relative might suffer through Aunt Edna’s annual culinary horror, consumer products get one chance — and one chance only — to hook their audiences’ taste buds. If the flavor doesn’t strike the right note the first time, there is little chance the consumer will come back for seconds.

The flavor industry, with upwards of $10 billion worth of annual global revenue, invests a considerable amount of resources to help customers get it right the first time. The challenge is that the American palate never stands still. Consumers delight in discovering new taste sensations. In “The Physiology of Taste,” author Anthelme Brillat-Savarin succinctly notes, “The discovery of a new dish does more for human happiness than the discovery of a new star.”

Consequently, as the American palate expands to include more global flavors and ethnic variances, these factors — coupled with demands for fortified foods, or nutraceuticals — increase the multiple variables flavor chemists juggle.

In addition to the new global flavor introductions and an increased interest in nutraceutical foods, certain processing methods used to manufacture foods today also take their toll on ingredients and flavors. Entire volumes are dedicated to the topic of flavor reactions, so this article will merely skim the surface of some broad topic areas. To begin, however, it is important to take a brief glance at the mechanics of flavor.

Mechanics of flavor
Flavor chemistry is comprised of one part magic and two parts science, with a touch of artistry tossed in for good measure. It’s no small wonder that artistry forms part of the mixture, because flavor itself involves a combination of more than one of the human senses. A symphony of proper reactions must occur for the right flavor sensation to dominate. Flavor involves a blend of chemoreceptions: first, through the oral sensations within the mouth, including gustation or taste; second, airborne chemical reception of olfaction, or the sense of smell; and third, mouthfeel. Among all this, don’t forget the visual presentation of the food as it appears to the eyes. Smell, taste and touch, or mouthfeel, act in concert, firing neuroreceptors in the brain to blend together for that overall impression known as “flavor.”

Within the past several years, various researchers, including neurobiologists, have continued to add to the body of flavor knowledge, narrowing down the particulars that create a more lucid picture of the brain’s reaction to this combination of gustation, olfaction and mouthfeel. For example, Robert F. Margolskee, M.D., Ph.D., identified proteins crucial for taste cells to detect sweet and bitter chemicals, discovering they are very similar to related proteins necessary for vision. Others have obtained evidence that nerve receptors or neurons in the brain can respond to more than one type of taste signal in the same way that nerve cells that process visual stimuli from the retina can react to more than one color.

Among taste perceptions, the traditional “big four” that we all learned about in school, namely sweet, salty, bitter and sour, have been joined by a controversial fifth, umami. Named by the Japanese, it loosely translates as “meaty” or “savory” and is the sensation elicited by glutamate, one of the 20 amino acids associated with protein primarily derived from meat, fish or legumes. In 1998, researchers Nirupa Chaudhari, Ph.D., and Stephen D. Roper, Ph.D., of the University of Miami, FL, claimed to isolate a receptor from rat tissue that binds to the amino acid glutamate and proposed that it underlies the umami taste.

Whether we’re inclined to accept a fifth taste sensation or not, the entire system doesn’t stop with sweet and sour. We also sense taste intensity, deciding whether it is pleasant, unpleasant or neutral. The trigeminal nerve carries feedback about all kinds of sensation, except taste, from the anterior two-thirds of the tongue; for example it transmits hot or cold sensations. And the neurons in the taste pathway record these food or flavor attributes simultaneously, much as those in the visual system represent shape, brightness, color and movement.

Speaking my language
Despite the scientific advances in identifying the specific pathways and receptors that evaluate taste or flavor, everyone still interprets them a bit differently. So how does everyone at the corporate dining table evaluate products in a consistent manner? Common descriptors help provide a bridge between the researcher, the marketing department and the consumer. This is the starring role for a sensory scientist, who uses analytical methods to evaluate particular ingredients or foods to provide a descriptive analysis. The end result is usually a common vocabulary or lexicon of words that describes a product or ingredient. This information can help marketers identify key attributes that drive consumer preference. In addition, because both marketing and the lab can use the same set of descriptors, clear communication helps marketing cohesively work with researchers and developers so they can fine-tune products or ingredients to eliminate or enhance certain flavor characteristics.

For example, the aroma profile for “grape” might include 25 descriptors, or for “red apple” a total of 17. Along with descriptive terms, flavor chemists will also link descriptive types, or specific brands or varieties of items, such as Granny Smith or bubblegum, when evaluating flavors or ingredients to make flavors easier for taste panelists to identify.

A look at the papers submitted annually during the Chicago-based Institute of Food Technologists’ Annual Meeting and Expo reveals that not all foods or ingredients are described using sensory-science techniques — much sensory work remains. Country ham, various fruit purees, tomato sauce, peanut flour, and commercial versus fresh soymilk all warranted extended sensory research in an effort to establish common descriptive terminology. One recent study attempted to provide definitive, common terms for describing the flavor, aroma and chemical feeling characteristics of rum products from Louisiana. The terms the panel developed included: artificial, almond, butterscotch, caramel, chemical (plastic/ rubber-like/painty), chemical/medicinal, cinnamon, fruity (banana), fruity (apple/pear-like), floral, fusel oil, leathery, pure ethanol, hickory-smoke, sweet, vanilla and woody.

As a further step in analysis and identification, scientists boil down common descriptive terms to their molecular level. Cornell University, Ithaca, NY, offers a website (www.nysaes.cor nell.edu/flavornet/ sensory.html) that divides descriptive flavor terms into categories, including aromatics, berry flavors and terms, citrus, and floral, to name a few. A simple mouse click on a selected term from one of these lists, such as “sweet” or “tallow,” shows the chemical compound and molecular weight related to the flavor. Under sweet, for example, the chemical-compounds list includes methyl 2-methylbutanoate, popcorn, 2-methylpyrazine and 2-acetal pyridine. Another click on the chemical-compound term and up pops the molecular drawing. The final molecular analysis of a flavor characteristic is what enables a flavor chemist to reproduce or alter flavor notes in the lab.

Some like it hot
Ask any food technologist about the most torturous process any set of ingredients can experience and the answer would be heat-treatment — for example, pasteurization or deep-frying. Julie Anne Grover, flavor applications technologist, Wixon Fontarome, St. Francis, WI, also adds high-pressure systems, such as extrusion, to that list. “The high heat or the high pressure acts to release the volatiles of the flavor,” she says. “We can try to protect the flavor using different carriers, or another possibility would be to create a flavor system that would develop during heat processing.”

One example of a developing flavor system is a Maillard-reaction flavor that forms volatiles during heating. The formulator can use the Maillard reaction to their advantage when the desired end-result is a darker, more-cooked flavor, such as in a caramel or chocolate product. However, allow the Maillard reaction too much time within a system, and even those darker, cooked notes can be overdone.

Bob McGorrin, Ph.D., professor of food science and technology at Oregon State University, Corvallis, comments that, in 2002, a research group in Germany completed work and published information that noted changes in fresh-brewed coffee over a 90-minute period. While the Maillard reaction contributes to color and positive coffee notes, they discovered that part of the reaction that produces color in the coffee can actually bind up flavor compounds.

So, while the Maillard reaction can produce desirable flavors and colors in many foods, it can also produce some undesirable effects. In foods that target a particular protein level and composition, formulators should also be aware that the Maillard reaction can cause the destruction of essential amino acids, particularly lysine.

Bob Eilerman, senior vice president of research and development at Givaudan Flavors Corp., Cincinnati, says one way to work with the heat is to develop a precursor system, or system designed to change when heated: “There are systems designed to fall apart when you heat them. Initially they may not be particularly stable, or they may look incompatible with the raw materials, but they are more compatible in a post-reactive system, such as extrusion and thermal treatments. Basically, you design components that are set up to either decompose thermally, or enzymatically fall apart into fatty acids or other materials by virtue of the processing system.”

This is very much an applications-specific flavor system, says Eilerman, customized according to the specific parameters, and even processing machinery, that customers use in the plant. The benefits of this customized system are many. “It gives both us and the customer an opportunity to create something relatively unique,” he says. “The flavor display is less likely to be able to be mimicked or copied by others. And you’re using the temperature as a friend instead of a foe.”

Dan Rosson, sales manager for T. Hasegawa USA Inc., Cerritos, CA, says strong-heat systems, such as deep-frying, also present flavor challenges for the formulator: “You might try to stick them (flavors) in some sort of predust to make it through the system, but once the molecular weight of the flavor chemical goes beyond 300, you don’t smell the aroma anymore. Flavor companies really are selling aromatics, and heat is an enemy because flavors can flash off.”

To protect flavored ingredients, most items destined for deep-frying receive a coating of breading. For example, the cheese in a popper appetizer is first protected by a layer of breading and then stuffed within a jalapeño pepper. The two layers surrounding the cheese help it melt, but prevent it from dispersing into the fat. Flavor can disappear during frying because the oil gets the flavor — it doesn’t remain in the product. Even in flavored french fries, despite the power of extrusion, one chemist indicated they have better luck maintaining some flavor in an extruded fry, rather than one that is cut and then deep-fried in oil.

Within pasteurization systems, a closed system is more favorable to containing flavor than steam induction. A closed system, even a UHT one, may volatilize the flavor aromatics; however, they can be automatically recaptured within a closed system. Rosson adds that systems now exist that can add the flavor load after pasteurization.

The best tip is to select a carrier for a flavor to protect some of the volatiles. Much depends upon whether the flavor is in liquid or powdered form. Flavor companies can protect spray-dried flavors using different types of carriers. Liquid flavors should use a solvent with higher heat resistance, such as propylene glycol.

Some foods are expected to behave well under both subzero and high-heat exposure. For example, newer encapsulation technology helps deliver a better fresh-baked flavor to frozen dough, bread and pizza crusts that must operate under freeze/thaw/bake conditions. According to Carl Pacifico, new ventures development leader for Balchem Encapsulates, New Hampton, NY: “Yeast-leavened bread has that certain aroma when fresh-baked that doesn’t easily survive the freeze/thaw cycle from the supermarket to the consumer’s oven. We can provide that through our encapsulation technology.”

Pacifico notes garlic as one particular flavor candidate for encapsulation technology, “because it blows off so easily in dough. Also, too much garlic destroys the gluten in bread. You can’t put enough of it in to flavor bread without altering the gluten and, therefore, bread texture. Encapsulate it and you can get a nice garlic dough that will survive the typical abuse cycle of freeze/thaw and bake, while delivering a great garlic flavor to the customer.”

Essential fortification tips
Fortification has taken the food industry by storm. Unfortunately, many essential vitamins and minerals pack extra baggage with them, such as a chalky or gritty texture and mouthfeel, or bitter, metallic — or just plain nasty — flavor. In general, the rule of thumb with mineral and vitamin addition equals out to: the smaller the serving size, the greater the added vitamins and minerals will impact the flavor. At a 25% DRI level, developers would find the ingredients’ taste attributes very strong. Smaller serving sizes, heavily fortified, often give an off-flavor to the finished product.

Calcium is one of the more popular food additives in recent years. Typically, this mineral doesn’t have an overwhelming effect on a fortified-food flavor, but in a bland system, certain flavors can arise. Processors can choose to add a variety of calcium salts to a system; each salt has unique characteristics that can affect the flavor of the end product. Calcium lactate and calcium gluconate tend to taste more bland. Calcium carbonate, typically used in a broad range of formulations, may come across as soapy or lemony. Calcium citrate, not surprisingly, may taste acidic and chloride salt can promote bitterness. Another choice, tricalcium phosphate, has a bland flavor, but a gritty mouthfeel.

Flavor houses call upon various methods to deal with unwanted flavor notes or characteristics of popular, or even obscure, additives with healthful profiles, but less-than-desirable flavor notes. One example of a popular, yet occasionally challenging, food ingredient is soy, with its undeniable beany flavor notes.

Bob Nelson, senior food scientist for Flavors of North America, Inc., Carol Stream, IL, participated as a panelist during a soy symposium, discussing the impact of flavor technology on product development, specifically as it relates to soy. “Soy is the most economical and efficient source of supplying the growing world population with good, quality protein, as a complete source of essential amino acids for human consumption,” he notes.

As a popular, growing ingredient, what can the flavor industry do to help formulators incorporate soy into food systems? Some of the role of flavor development depends upon the exact nature of the ingredient, the processing conditions and the type of product being made. For example, the flavor of soy is most compatible with a grain-based product and shows success in this type of system. In addition, as the protein level increases in various soy products — from soy flour with about 40% to 60% protein, to 90% for an isolate — the negative flavor elements decrease.

However, soy flour tends to have higher thiamin content than other protein sources; thiamin can cause flavor problems in food products. Heating soy denatures the protein, which releases more thiamin notes that can further create negative flavor impressions.

Covering and encapsulating
Reaction flavors offer one method of dealing with negative flavors, Nelson suggests. A reaction flavor begins with a number of chemicals, usually amino acids and fat-based chemicals, blended together and subjected to heat, temperature, time and pressure. This provokes a chemical reaction that changes the character of the flavor to produce the desired end, such as a chicken flavor. The food scientist adds the flavor system or reaction flavor to the food formula, then subjects it to the required blending and processing to make an end product.

Some reaction flavors are nonsavory; however, reaction-flavor systems usually produce flavor notes in the savory or dairy categories. Flavor companies can complete a reaction-flavor system prior to delivery, or design it to finish full flavor development within the customer’s formulation.

Masking, another popular method of dealing with unwanted flavor notes, doesn’t bind or react to the flavor notes within the product. Rather, it covers it up or works over that undesired note as the term suggests.

“Personally, I think the greatest challenge might be a soy beverage; because they are so light in character the beany notes can come through very strongly,” says Grover. Companies such as Wixon Fontarome offer flavor modifiers to help mask soy ingredients’ beany notes. The flavor modifier used depends on the type of note the customer attempts to mask. “We can, in addition, add a modifier that can give the perception of a creamier product, to counteract an ingredient that might have a gritty texture,” she adds.

Encapsulation technology is experiencing growth in the areas of vitamin and flavor delivery, especially when the vitamin could cause off-flavors within the foods. Encapsulation usually involves a GRAS-approved and technically tailored hydrogenated-vegetable-oil coating for the process to deliver its load within the food system at the point where the body should digest the nutrient. “Encapsulated wellness ingredients not only provide control to avoid off-flavors within the food, but also can help control interactions or the potency of the vitamins, minerals or probiotics added to the food product,” says Pacifico. An example showcased by Balchem at a recent trade show included flaxseed, a source of omega-3 fatty acids, which usually deteriorates and loses efficacy during the manufacturing process.

Some might consider encapsulation technology as another form of masking. Pacifico cites guarana as one example. A native of Brazil, it serves as a popular source of tetra methylxanthine, which is similar to caffeine, theophylline and theobromine, a combination stimulant/euphoriant found in chocolate (the darker the chocolate, the higher the concentrations). “I understand that guarana within Brazil has a nice, pleasant taste,” he says, “but when dried for export it becomes bitter, with a strong aftertaste. There are manufacturers who are putting guarana in chocolate bars, yet even with the sugar and fat mimetics in that bar, the bitterness can have a big impact on people when eating it. That’s where we have helped with encapsulation technology.”

Selected coatings within encapsulate technology offer varying release mechanisms. The type of coating selected, as well as the techniques used on the substrate, depend on the type of application desired by the end user.

Warring amongst themselves
Sometimes flavors react with each other. At other times, ingredients — subjected to heat, pressure or even storage over time — will react in a negative fashion.

Some aldehydes combine with acids under high-heat conditions to form esters, which themselves have distinct aromatic qualities such as pear or peach. These are easily oxidized or dissipated when subjected to increased temperatures or wet conditions in a formulation. Some of the sweeter-smelling, more-delicate aldehydes (caramel and/or malt) can dissipate rapidly when exposed to the air. Again, if this reaction is intended, it works to the formulator’s advantage; however, all too often the reaction is unintended and adverse flavor results.

One example of a somewhat tricky flavor is cherry, mainly composed of benzaldehyde. It can react with alcohol or organic compounds within other flavors, to form acetals. Cherry is a popular flavor blended into juices and fruit punch, and Grover indicates some end-users prefer to mix their own flavors from different sources to maintain a proprietary position on their formula. However, if one company uses propylene glycol as a flavor carrier for strawberry and mixes this with a cherry flavor, this can spur a reaction over time.

As Nelson notes, however: “There are flavor interactions that we haven’t studied and still don’t understand. One example might be strawberry flavors in UHT milk. No one yet can get a strawberry through UHT that is the same quality as when it goes in.”

Peter Mazeiko, vice president of research and development for Ottens Flavors, Philadelphia, says: “Any time you put together a mixture of chemicals, you have the potential for an adverse reaction. Put an acid and an aldehyde or alcohol together, and you could be forming esters. Sometimes you might want that to happen, sometimes not. Mix propylene glycol, a common solvent, with any aldehydes and, if not controlled, you could form undesirable acetals. Some nuances of this reaction can taste like bug spray, some others you may want for complexity in your formulation.”

Packaging, shelf life and storage form too broad a topic to be included here. However, these do have great effect on flavor and require careful consideration when formulating a product.

The spirit of adventure
While any flavor chemist embarking on a new project can sense some excitement over a new challenge, the spirit of adventure comes alive over details of global searches for new flavors. Eilerman has participated in his company’s global search for new flavors called TasteTrek®. Hovering over the rain-forest canopy in Central Africa, or another exotic location, the scientists capture and bring back potential flavors to the laboratory with special equipment.

Their discoveries are multifold, says Eilerman. Researchers might find new fruits or unique natural products that provide new raw materials, and perhaps components, to insert into flavors to make them unusual and different. “We might discover anything from unique taste properties to unique sweetening abilities, or find creative ideation from viewing new construction and composition techniques that nature provides,” he adds.

They also search for new, global cuisines that either a customer has requested or might interest the exploratory American palate. Sometimes the new flavors work and sometimes they don’t. Processing techniques, pH or other factors might scratch a potential flavor off the list. “For example,” says Eilerman, “if the new flavor is proteinacious in any way, perhaps you’re retorting it in a beverage and it gels. It could decompose, or oxidize to change flavor — we have a number of hurdles to overcome.” However, these treks lead to exciting new flavor discoveries that can and do work. “The consumer in the U.S. has a very intense interest and curiosity, a willingness to try new cuisines. We can bring these back to the U.S. from our trips,” he notes.

In addition, Eilerman says the company has discovered flavors that can help mask the negative flavor notes of otherwise healthful ingredients. One exciting area of discovery from the overseas treks might be trigeminal materials that can change the way a consumer perceives a particular taste, or can act as a masking agent. The trigeminal properties might increase salivation, for example, and that can also impact the way a consumer perceives a given food.

Acids, sweeteners, lipids, oh my!
The chemical components of the ingredients themselves obviously affect the flavor system, interactions and release. Flavor-based interactions do occur, depending on the system’s pH. Flavor/acidulant interactions can occur most frequently in beverages, where the addition of acids provides tartness. Here, choosing the acid in a product can affect flavor perception. Naturally occurring acids in a juice beverage also affect how the flavor is perceived. Designers commonly use citric and/or malic acids with strawberry flavor, and pair tartaric acid with grape. Each acid has its own impact on the system’s overall flavor. An acid that works well with one type of flavor may not necessarily be the best choice for another flavor or blend.

Flavors interact with carbohydrates, and sweeteners have their own impact on flavor. High-intensity sweeteners — for example, aspartame or sucralose — have varying levels and types of aftertaste that must be treated in an individual manner. Flavor modifiers can help provide a sweetness profile to mimic real sugar. Manufacturers may even turn to sugar-masking agents when a formula is too sweet and the customer would like to have the sweetness reduced.

Fat influences taste perception, and flavor/lipid interactions also impact product stability, shelf life and taste. For instance, in a powdered formula fortified with iron and containing lipids, the fat reacts with the iron, causing catalytic oxidation of the lipids and resulting in rancidity.

Basically, any ingredient used in a food formulation can interact with each other or the flavor system. The best solution for the formulator is to work closely with their chosen flavor house from the very start of the formulation process, with full disclosure of the type of ingredients being used, to find the best flavor system for their product. Most flavor companies, if not all, will be happy to sign a confidentiality agreement.

Most of the flavor chemists could not stress strongly enough how helpful the element of open communication is in the working relationship. As an example, Mazeiko recalls trying to develop a flavor system for a cream-based filling. Using the ingredient information supplied by the customer, time and again his team developed a flavor, only to have the client reject it once he tested it in his own plant. “Finally, during a phone conversation, he indicated that, in addition to the other ingredients he gave us on his formulation list, he was adding 10% soy protein to the base,” he says. “This can significantly dilute the flavor’s effectiveness in a product.”

Back to the future
Looking to the future of flavor development, Mazeiko sees the challenges and opportunities increasing: “Flavors are being called on to do more than ever before, including providing richness and mouthfeel; fat mimetics; salt replacement or enhancement; soy or vitamin masking; bitter blockers; you name it. This challenges the industry, but also provides us with greater opportunities.”

Recent advances in genomic science could have a significant impact on flavor chemistry, according to Eilerman: “Genomics have created a whole new vista for flavor companies, by mapping both olfactory and taste receptors. This opens a new frontier. How far this will take us into the investigative area of receptor biology, to improve taste and aroma of food products, I don’t know, but it looks pretty interesting, at least from the science side.”

Then again, success or failure of a particular flavor treatment, even in the future, might depend upon trial and error — multiple tastings until everyone on the development team agrees that they have a winner.

As to the effect on the industry of multiple ethnic tastes landing on the shores of the United States, it all depends on attitude. Some in the flavor industry say manufacturers can consider the new tastes as a challenge, or as an opportunity. They note that 20 years ago, not many consumers ate salsa with their chips; yet look at today. Manufacturers can shrink from these trends or embrace them. And imagine being with the company that embraced that trend and ran with it.

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