April 28, 2008
Flavor modulation sounds like an esoteric principal, but truth be told, we all have a touch of the flavor chemist in us. Even my mother betrayed an unwitting knack for the flavorists art in her scheme for making my siblings and me eat our vegetables: Just douse them with ketchup. As a flavor-masking technique, her ketchup offensive was a bit blunt, but according to Mariano Gascon, vice president, R&D, Wixon Inc., St. Francis, WI, it was not without logic.
It makes a lot of sense, says Gascon. If you think about it, one of the phenomena that operates in taste modulation is taste-blocking. There are substances that have the property to block tastes, and one of them is eugenol, which is present in the clove that is used as an ingredient in ketchup. That has the property literally to just numb your receptors.
The nutraceutical witches brew thats made the kitchen an annex of the medicine cabinet presents trickier neutralization tests than mere ketchup can tackle. Fortunately, advances in flavor modulation have kept pace with the flavors being modulated.
Companies have been working at it longer, so just by sheer concentration of effort, new technologies have been found, says George Lutz, quality assurance/technical services manager, Cargill Salt, St. Clair, MI. Its opened up a whole new basket of ingredients that, to be honest, the product developer gets to play with. Just having more tools available enables them to do some unique things.
New challenges, old solutions
Taste masking is embedded in our culture, says Gascon. Mary Poppins told you to add a little sugar, and it made the medicine go down. Similarly, chefs have long corrected an off-balance recipe by sprinkling in sugar, salt or vinegar.
A judicious inclusion of fat can hide a multitude of sins, too, as Kim Gray, Ph.D., senior applications scientist, Givaudan Flavors, Cincinnati, explains. A perfect example is milk chocolate, she says. The cocoa itself is extremely bitter, but add some fat and sugar and you get milk chocolate, which is very pleasant.
The off notes targeted most for masking are many. Some artificial sweeteners are notorious for bitter, metallic, lingering notes, says Greg Yep, vice president of global application technology, Givaudan. He cites caffeine as another bitter offender. Nutritional ingredients present the biggest headaches, with B vitamins giving off a rotten-egg taste thanks to sulfur groups, and minerals lingering on the palate as metallic or bitter. Casein comes in for criticism as bitter and soapy, and soy proteins can also taste notoriously bitter, as well as grassy and reminiscent of hay, he says. Rounding out the list, tannins and catechins, popular antioxidants, are bitter; omega-3 fatty acids can taste fishy; and the nutraceutical market in general, he concludes, just tastes mainly bitter.
But as consumers show more interest in these ingredients, the demand for functional products has seen tremendous growth, says Markus Eckert, vice president, technical, Mastertaste, Teterboro, NJ. In the past, consumers seeking healthier products were willing to forgo taste in exchange for the health benefits offered by these products. Now that this trend has hit the mainstream public, food and beverage manufactures have begun dealing with a new consumer for whom taste is the top priority.
The physiology of taste
Traditionally, a brute-force approach of drowning out off notes summed up the industrys standard for ameliorating objectionable flavors. And, while dumping in sugar, salt, or heavy, sweetish flavors like peanut butter, vanilla and chocolate can mask some bitterness and off notes, just piling flavor atop flavor leaves a lot to be desired. For one, its costly. For another, its superficial, as an initially appealing flavor can fade in the shadow of more objectionable off notes. And, adds Gray, in the past, many of these masking agents covered up the entire taste of the product, and not just the off notes.
In their search for 21st-century solutions that appeal to 21st-century palates, researchers have turned to the physiology of taste for answers. The use of receptor technology has allowed some companies to selectively screen ingredients that mask the off tastes right at the taste buds, says Gray, thereby tailoring the solution to the problem. Conceding that were not completely there yet, she says, this approach can, in the future, be fine-tuned just to block the off notes and not suppress the flavor.
At the vanguard of the revolution are companies like Senomyx, Inc., San Diego, CA. Were trying to translate what people taste into the biology of taste, says Mark Zoller, Ph.D., chief scientific officer, Senomyx. That means understanding how taste buds work, and then understanding the proteins that mediate these tastes. The company has discovered that taste buds are composed of mixed cells that sense the individual tastes, as opposed to the old theory of single-sensation taste buds. These cells operate in either a lock and key mode where the tastant binds to the receptor and triggers the neurological response signaling a specific taste, or a channel and pore system where ions that create sour and salty move through pores to trigger the response.
Sugar, but sweeter
In the case of sweetness, Zoller says companies want to enhance sucrose to reduce the amount of carbohydrate you use, so it doesnt have as many calories, while still tasting like sucrose. What our biochemical assays allow us to do is, basically, to serve as a filter. Im only interested in the samples that actually trigger or do something to the receptor, and thats fairly rare. Still, the company has compiled a library of about 500,000 samples of sweetness enhancers, both synthetic and natural.
Recent movements to reduce sugar have influenced R&D, especially in products for children and in drinks containing juice, says Eckert. With children in mind, we are working with processors on carbonated beverages and dairy beverage applications where the focus is clearly on formulating with less sugar. The companys sweetness enhancer, based on natural FEMA GRAS flavor materials, he says, is not an artificial additive like aspartame or saccharin, nor is it meant to replace the natural sweetener. Rather, he describes the technology as synergistic, meaning that the primary sweetness impression on the taste buds has to come from the product, or from sugar itself. The flavor modulator potentiates this signal and increases the perceived overall sweetness of the product.
Symrise, Teterboro, NJ, released a sweetness enhancer that uses the carbohydrate present in an existing formulation to affect an interaction with the tongues own sweetness receptorsultimately stimulating a sweeter taste.
By making the sweet taste of a given amount of sugar go farther, not only can a formulation use less, but it can omit artificial substitutes. High-intensity sweeteners tend to have very characteristic sweetness profiles that leave a lingering aftertaste, which some consumers perceive as bitter and artificial, says Eckert.
One of the things weve found from our science is that different sweeteners bind to the receptor in different ways, Zoller says. Were trying to understand whether if, when these sweeteners bind to the proteins, theyre getting stuck. One of the ideas about the lingering of the sweeteners is that maybe they just stick on the receptor too well. Alternatively, maybe theyre sticking on the membrane of the cell. Those are the kind of mechanistic studies that were trying to do.
Stretching the salt
Such stickiness might account for the bitter aftertaste of salt substitutes like potassium chloride. Its bitterness, its metallic tasteit just doesnt have the same effect on the taste bud, Lutz says. And thats why true saltiness is so hard to replicate: Certain taste buds are a target for the compound salt. And if it doesnt match up to that receptor, then its not received in the same fashion.
Another approach, Zoller notes, is trying to boost other flavors to try to fool people into not realizing that theyve taken out the salt. Witness the use of umami-enhancing ingredients like monosodium glutamate (MSG), yeast and vegetable extracts, and the nucleotides inosine monophospate (IMP) and guanosine monophosphate (GMP) in reduced-sodium foods.
One tactic is making the salt receptor more efficient. Zoller likens the sodium ion channel to a hose, but it actually has a limit to how much sodium can pass through at a given time. Were trying to increase the rate at which the sodium flows into the cell over a given time, so that you can still get the same signal, but reduce the amount of sodium you need to get it. This isnt a salt substitute: Its trying to make the salt we use more effective in what it does, he says.
Researchers at FONA International Inc., Geneva, IL, are also looking at making low-sodium formulations taste saltier on their own by focusing on all its attributes. In other words, says Robert Sobel, Ph.D., director of technology and innovation, FONA, we ask what happens when you put salt in your mouth. You get a watering sensation. You get a mouthfeel sensation.... Its just a matter of understanding the physiological response of the body to salt, and seeing if you can build things around that to enhance it. How can we enhance this salt signal without adding the extra salt? What can we do to amplify that response?
For its part, Cargill Salts entry into the sodium-reduction contest isnt just an enhancer, Lutz says. Its actually a sodium-reduction system. The system is a limited deck of common GRAS ingredients that allow for sodium reductions in the range of 25% to 50%, he says.
The bitter end
To enhance salty and sweet sensations, researchers are trying to block bitternessto an extent. An appreciation for hoppy beer, strong coffee, peppery greens and high-cocoa chocolate, for example, can bring sublime pleasure. Our approach is that, rather than block all bitterness, first were identifying the types of bitterness people dont like, and then were picking out the bitter receptors that correspond to that, Zoller says.
The strategy prevents the keythe bitter compoundfrom tripping the receptor lock. Were looking for a special key that doesnt trigger the lock, but still fills the space, Zoller explains. Its like putting Super Glue in the lock. Among the many compounds that trigger bitterness, Senomyx has narrowed its search to two novel receptors, one that responds to 6-nitrosaccharin, a derivative of saccharin, and another sensitive to both 6-nitrosaccharin and denatonium, one of the most-bitter substances known.
Mastertaste is also taking a biochemical approach to fighting bitterness, particularly from high-intensity sweeteners. We have worked in flavor modulation geared toward masking bitter off notes by manipulating the bitter receptors and increasing the sweetness perception using natural flavor ingredients that not only contribute to the overall flavor profile, but also bind to the taste receptors on the tongue to give the desired overall taste impression, says Eckert.
Pulling off the mask
Sobel is quick to distinguish tactics of taste blocking from the process of flavor masking. The term blocking refers to an actual physical interaction on the palate where you have chemicals that are blocking the taste receptors on the tongue, he says. In masking, youre not using something thats going to physically bind to the taste bud to block that perception. What youre doing is using more of a psychological impact of competing responses from both the nose and tonguebecause the flavor attribute is really coming from the nose; the taste attribute is really coming from the tongue.
In other words, youre playing head games. Masking really takes advantage of understanding that psychological response in the brain, Sobel says. All signals going from the tongue, and also from the olfactory bulb, compete for time within the brain, he explains. To mask caffeines bitterness, he says, you could go ahead and put a flavor in theresomething like a vanilla flavor, for instanceat a very low level. This confuses the brain to preferentially perceive the vanilla flavor, because the brain, from a very early age, is trained to like vanilla flavor.
Flavor modifiers have little or no taste of their own, says Gascon. They are chemicals or extractives or substances that have proven to have an effect on the way you perceive food. They complement, enhance or modify the flavor of what you use them in, he says. They do so through mechanisms such as adaptation (fatiguing the palate on a particular taste or flavor), cross-adaptation (raising or lowering the perception threshold for one substance by fatiguing the palate on another), taste-blocking (literally blocking the ability to perceive certain flavors or tastes), and taste modification (completely changing a taste or flavor perception from whats expected).
Sometimes a stealth flavor modifier needs help. Flavor chemists may start with a silent base and accessorize it with identifiable flavors. Ray Hartman, senior flavorist, FONA, calls this flavor pairing. A good example would be if youre trying to block bitterness in some type of product, he says. So you use a masking agent to mask or offset your bitterness, and then you pair it with a grapefruit flavor to meet consumers expectations for bitterness, because grapefruit actually has its own bitterness.
Similarly, Sobel worked on a product that had a sulfurous off note, he says. Mango flavor solved the problem. Because mango carries a slight sulfuric note of its own, it piggybacks onto the undesirable sulfur and brings it over to the acceptable side.
Matching like with like isnt the only option, says Jean Gallagher, technical solutions manager, FONA. It may be something where you want to pair known and unknown so that youre sending something of a confusing signal, if you will, she says. Its disruptive, and yet pleasant.
Sometimes, masking may not be the biggest obstacle. I think the hardest challenges arent so much covering up off notes, Sobel says, but matching the temporal width of a flavor perception. Consider the example of a caffeinated chewing gum. While a masking system based on cinnamon is a common solution, the issue then is that the cinnamon flavoring doesnt last long enough, he says. So what happens is the caffeine starts to come through after you start chewing for a while, and then you have to start exploring other options of how you get flavor duration to occur.
Modifying from the ground up
Matching the desired profile with the starting base is the only way flavor modification works. We always look at the end product and keep that in mind throughout the process, Sobel says. By understanding the overall complexity of the finished product, that gives us a better strategy for how to approach it.
Processing and storage are always important. Heat, preservatives and so on will influence the off-note formation in the finished product, says Yep. Also, you dont want the processing conditions to cause unnecessary reactions. Sometimes off notes dont really get pronounced until the product has been on the shelf or exposed to light. So a masking system may need to be developed to handle future off notesnot necessarily just the taste of the product right off the line.
The take-home message is nothing new: Flavor modulation is best pursued on a case-by-case basis. Theres no one silver bullet thats going to address the issue of difficult ingredients, nor is there any one flavor that is going to do the job adequately, Gallagher says.
Thats why there are a lot of different approaches, adds Hartman. Theres masking, theres flavor enhancement, there are modifierstheres just not one pathway to success on these projects. You could use compounds that block taste on the tongue. You could use ingredients that work synergistically with other compounds or other basic tastes. There are multiple ways to tackle the problem. At the end of the day, whats going to define success is whether or not this product is preferred.
Kimberly J. Decker, a California-based technical writer, has a B.S. in Consumer Food Science with a minor in English from the University of California, Davis. She lives in the San Francisco Bay area, where she enjoys eating and writing about food. You can reach her at [email protected].
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