Flavor: How Much Do We Really Understand?

The key to designing exciting new products with attractive flavors that will achieve continuing market success is to understand consumer needs. Increasingly, this is accepted as a statement of fact and not as an opinion but, if consumers are the key, do we really understand what they are telling us when probed on their likes and dislikes? Further, do we professionals in the food and beverage industries really understand the words we are using? These are not academic musings; as communications between operating functions improve (especially between marketing and technical functions), we find ourselves having to question our understanding of the words we use before we can translate their use into a consumer environment. The enormous importance of flavor to consumer choice has triggered a revolution in our understanding in recent years, and some of these developments will be outlined below.

The Flavor Pyramid

The characteristic flavor of foods is formed from the contributions from hundreds or even thousands of individual chemical species and, many times, the characteristic food flavor is influenced strongly by minute levels of certain key chemicals (often at levels less than one part per billion). The stimuli long have been classified into tastes and odors and, more recently, the importance of trigeminal stimuli has been recognized. The contributions of these classes to flavor can be shown diagrammatically as seen in the chart “The Flavor Pyramid.”

The foundations of any flavor are the involatile chemicals dissolved in saliva and detected in the mouth, commonly called the basic tastes. Unfortunately, a widely propagated misunderstanding is that the basic tastes are perceived only on certain locations on the tongue. This is not true. Although some regions are more sensitive than others, tastes can be perceived over much of the tongue, as well as on other soft oral surfaces, such as the palate and the throat. We also now recognize the need to expand the four basic tastes that have long been recognized (sweet, salt, sour, bitter) to include umami, the sensation from MSG and other flavor enhancers. The importance of the contributions of these stimuli to flavor should not be underestimated. For example, bitterness in the right context (such as coffee and beer) is essential to enjoyment, yet, in the wrong context, it is a source of consumer complaints. Sensitivity to bitterness is a genetic factor, and three populations have been identified (non-tasters, tasters and supertasters), giving new product development (NPD) teams an uncomfortable consumer segmentation to address. In addition, it becomes even more complicated when realizing that the segments can differ in different ethnic groupings.

Perhaps more research has been carried out into sweetness response than any other basic taste (not surprising, in view of our inherent liking for sweetness). The understanding also has been driven by the perceived need to reduce dietary sugar, and the consequential need to address the taste defects that often afflict sugar replacers based on intense sweeteners. Work carried out at Leatherhead Food International (Surrey, U.K.) as part of E.U.-funded projects has identified design strategies that can be used to minimize unwanted tastes and to maximize sweetness quality. (See “A Design Strategy for Sweetness Quality” chart.)

More recently, attention has focused on salt taste, primarily as a consequence of the need to reduce dietary salt intake for health reasons. Compared with sugar replacement, options are more limited, as no material has been identified that can deliver the clean, salty taste of sodium chloride, and relatively few with any salty taste at all. However, pressure to reduce the salt content of foods has continued to increase, and Leatherhead is examining various options.

Aroma Volatiles

The basic tastes provide the foundation for the aroma volatiles that give the interest and variety to foods. In contrast to the limited number of basic tastes, there are many thousand chemical species that deliver an odor response in the nasal cavity, and these are essential in building flavor variety. Scientists also are learning much more about how these volatile chemicals are perceived, particularly how they reach the receptors in the nose when foods are consumed--this is discussed in more detail in the area on flavor release.

Trigeminal stimuli have received less attention than other stimuli but are important in delivering excitement to foods and drinks. These stimuli trigger the trigeminal nerve responsible for the pain response to heat and cold. The chemicals that cause this are present in ingredients such as pepper, horseradish and chili, but this response also is produced from alcohol and the carbonic acid that is formed on carbonation of soft drinks. In an age in which consumers are experiencing sensations from foods encountered in foreign travels, it is not surprising that this stimulus is finding itself employed in unusual circumstances--for example, in the use of chili in fruit-based soft drinks, as well as in alcoholic beverages.

Sensory Interactions

Until recently, it has been common to investigate and describe the sensory quality of foods in terms of their individual sensory modalities: appearance, flavor and texture. It has now become widely accepted that this is an incomplete way of addressing perceived sensory quality, and it ignores the interactive nature of how consumers use their senses.

The effect of appearance on flavor perception is well known and used in the industry. For example, the use of a yellow food coloring in a plain white ice cream will increase the apparent intensity of flavor attributes. Other aspects of the appearance effect are less well understood--for example, how other appearance characteristics, such as reflectance properties and opacity, might influence flavor perception. Appearance also has an influence on perceived texture--sometimes known as visual texture. The sounds emitted from foods when broken, either in the hands (for example, chocolate) or in the mouth, also can be important in the perception of texture, especially in foods which are crispy or crunchy. The question of whether emitted sounds might influence the perception of flavor has been raised but has not been the subject of research. Perhaps it is unsurprising that even within a modality, interactions are evident, especially the complex stimulus that is flavor. The presence of one aroma compound can influence the perception of another, and similar interactions are found between the basic tastes. However, one of the most important interactions, and one that has been subject to many investigations in recent years, lies in the relationship between texture and perceived flavor, which has a tangible physical basis and influences how flavors are released from foods.

Flavor Release

Consider the events that take place when a solid food is bitten or placed in the mouth. Initially, the only flavor response comes from the volatile components coming from the external surface of the food. Once the food is sheared or crushed by the teeth, a series of events is triggered, resulting in the release of tastants, aroma volatiles and chemical irritants that are perceived as an overall flavor response. Other events also will contribute to this response. Increasing biting and shearing increases the effective surface area of the food and releases more flavor components. Saliva is injected as a lubricant to aid chewing, and this acts first as a solvent for the tastants, and second as a diluent. Temperature changes alter the form of the food: cold foods such as ice cream melt, fat in products such as chocolate melt and liquid components of hot foods can solidify.

A major consequence of this catastrophic series of events is that flavor is not perceived instantaneously. Flavor builds up from a zero level, reaches a maximum and, following a plateau period, falls away. However, since flavors are comprised of many chemical stimuli, if the character of a flavor is to remain constant through the time in the mouth, all the key flavor components must be released in harmony. The consequence of an unbalanced release is shown in the chart “Flavor Release.”

The consequences of imbalanced flavor release were seen in the development of fat-reduced foods in response to the health-driven need to reduce dietary fat. Many fat-reduced products were designed to mimic the textural characteristics of their full-fat equivalents but failed to deliver the required flavor characteristics. The need for solutions to these problems initiated research into the links between structure, composition, texture and flavor. This resulted in both an improvement in the flavor of the second-generation commercial products, and also the recognition of the boundaries of consumer acceptability (they reject products without acceptable flavor, despite the dietary benefits). Sophisticated methods now are available to investigate the relationship between the release of flavor components in the mouth and their perception: these use a combination of in-mouth measurement with measurement of sensory response using time-intensity methods.

Practical Consequences

The most important single message that has emerged from recent research is that we can no longer place the different sensory modalities into compartments and investigate them in isolation. Consumers integrate all the sensory responses they are receiving and process them into a simple binary like/dislike response. If the industry is to understand and respond to changing consumer demands, these interactions must be recognized and understood. This requires research into the drivers of consumer acceptability, into the psychology of sensory response and into the biological basis of sensory perception.

Perhaps one of the more unexpected manifestations of this interest has been in the area of gastronomy, in which a combination of physicists, food scientists, food writers and chefs has driven interest in the science of gastronomy. These molecular gastronomers, as they have been called, have applied scientific principles to cooking to such an extent that chefs creating new eating experiences have achieved international acclaim. Heston Blumenthal, proprietor of the three Michelin-starred Fat Duck (Bray, U.K.), has been instrumental in leading these developments and has worked with ingredient companies to create radical new flavor and texture combinations. Ironically, the food industry now is investigating how such novel combinations can be adapted for the mass market.

Functional Foods and an Aging Population

In this highly innovative area of the food industry, considerable interest is being devoted to understanding sensory response. This is largely a consequence of the realization (partly as a consequence of some spectacular product failures) that functional foods will achieve success only if their eating quality achieves parity with that of conventional foods. This can be difficult to achieve if these foods contain ingredients in sufficient quantities to deliver nutritional and health benefits, but which have questionable sensory qualities, such as minerals, amino acids and peptides. There is a specific focus on bitterness and how it can be masked, but also in how flavors interact with these ingredients.

Within the next 25 years, it is projected that the percentage of the European population over the age of 60 will be over 25%, and there are concerns that, as a result of a combination of a number of factors, many elderly people will not have a nutritionally balanced diet. One contributory factor is thought to be the loss of sensory response to specific tastes and aromas. While this is known to occur in the elderly, the consequences in terms of enjoyment of food are less understood. This aspect has been a major focal point of the E.U. HealthSense project, which has been running for three years and which has involved 24 research centers in 10 countries. In common with the holistic principles outlined above, this project has been multifactoral in nature, investigating many factors likely to be interactive in nature. The Leatherhead role has involved the investigation of texture-related eating difficulties, which are likely to give rise not only to chewing and swallowing difficulties but also to loss of interest in eating through restricted release of flavors.

Future developments in the effective use of flavors will depend largely on the understanding of the nature of flavor itself and how the various components are perceived. This will be achieved by a multidisciplinary effort that addresses not only the perceptual aspects but also their relation to food structure and texture, and how these change during the time the food is in the mouth. This holistic approach carries the promise of solving many of the current problems in delivering flavors that satisfy consumer demands for quality, as well as a strong demand for healthy eating.

David Kilcast, B.Sc., Ph.D., FIFST, CSci, is business development manager for Sensory and Consumer Science at Leatherhead Food International (Surrey, U.K.). His team provides sensory, instrumental and consumer research and testing services for practical applications and has written and lectured extensively on the subject. He is a founding member of the Erice Molecular Gastronomy Group. He can be reached at + 44 1372 822 321 or dkilcast@leatherheadfood.com.

Leatherhead Food International is a global and independent provider of food information, market intelligence and technical and food research services delivering consultancy services varying from large-scale government research through customized client information projects to nutritional, sensory and consumer studies.

Sidebar: Going Global

North American food manufacturers increasingly offer exotically flavored fare typical of foreign lands. However, food manufacturers, both foreign and native, also are interested in providing prepared foods in emerging nations with a growing middle class.

For example, ITC Foods is privately owned by ITC Ltd. (Kolkata, India) and is a recent entry into the food industry. Bloomberg.com quotes ITC's net income fourth quarter 2004 net profit as 4.49 billion rupees ($99 million), up 16% from the year before, primarily due to cigarette and lodging sales. Under its premium brand, Kitchens of India, the company is eyeing not only its own market but, according to regional chief executive (Foods Division) Ravi Naware, "We are currently in discussions with a number of large retail stores, gourmet shops, delis and stores specializing in ethnic foods from different countries," as quoted in The Hindu Business Line in October 2003.

In 2004, Mintel's GNPD (Chicago) noted Kitchens of India introduced 100% natural Chicken Darbari with chicken chunks in a butter-laced tomato gravy and an ingredient legend that sports tomato ingredients, garlic, white butter, ginger, khoya, cashewnut (cashew), salt, sugar and rose petal powder. Its ready-to-eat Mirch Ka Salan dish is “made from succulent whole chilies in a thick gravy of roasted peanuts, almonds and sesame seeds.”

Another hot idea comes from Indosentra Pelangi, which introduced Bumbu Kentang Goreng Seasoning for French Fries into its domestic market in 2004. Its ingredient legend boasts sugar, salt, cheese, flavor, chili powder, pepper and MSG as taste enhancers

Taste sensations come from developed countries, as well, of course. Ito En's (Toyko) Jujitsu Yasai launched a juice that has “warming effects for the winter,” with apples, lemons (including Chinese lemon), carrots, spinach, ginger extract, chili and flavor.

--Claudia D. O'Donnell, Chief Editor

PHOTOS COURTESY OF MINTEL'S GNPD