The Importance of Aroma

Flavor and aroma are inextricably tied together, making the ability to detect and distinguish specific aroma and flavor components crucial to sensory analysis.

"Formulating any type of food or beverage involves more than just one's sense of taste," says Stephen Manheimer, marketing director for Mastertaste (www.mastertaste.com), Teterboro, N.J. "You have to consider aroma, texture (mouthfeel) and, in many cases, even appearance. All of these factors contribute to the overall sensory experience that the consumer has when he sits down to eat. Aroma in particular is strongly linked to taste.

"The taste buds can only perceive five stimuli: salt, sweet, sour, bitter and umami   that is, 'savory' or 'meaty'," Manheimer continues. "Because of this, a lot of what consumers experience when eating actually occurs through their sense of smell, not taste. The natural question that comes to mind is, how do we perceive odors or aromas?"

In 2004, neuroscientists Richard Axel of Columbia University, New York, and Linda Buck of Fred Hutchinson Cancer Research Center, Seattle, shared the Nobel Prize for Physiology or Medicine for their contribution to our understanding of how we detect odors. Before they published their work, olfactory scientists knew the cells lining the nose bound a variety of molecules responsible for aroma.

These cells relay electrical signals to a specialized area of the brain called the olfactory bulb, which in turn shuttles messages to the brain's smell recognition center. However, which receptors on the cell's surface are doing the work and how exactly these signals are relayed had remained a mystery.

Axel and Buck showed the detection of aromas is highly specific: Each aroma molecule activates a specific receptor on a particular membrane cell of the nasal mucosa. When an aroma molecule binds to a receptor, it sets off a sequence of events involving special signal proteins, called G proteins, which control the opening or closing of channels in the cell membrane.

The surprising discovery was that each cell lining the nasal cavity displays only one type of receptor on its surface, which in turn can be activated by only a handful of related aroma molecules. Since most odors consist of many molecules that activate different receptor-bearing cells with different intensities, we can recognize about 10,000 different aromas.

Axel and Buck further showed the receptor-bearing cells send projections directly to the olfactory bulb. This helps to explain why we are so immediately sensitive to odors, and why separating taste from odor in food is next to impossible.

Most odor molecules are volatized organic compounds. Odor compounds form naturally during the ripening of plants, the development of oils or during natural processes such as fermentation. The list of known natural odorant chemical bases is extensive, ranging from alcohols, aldehydes, amines, esters, ethers and essential oils - anything that can evaporate and reach concentrations high enough for detection. Once identified, the chemicals responsible for aroma can be captured and utilized to enhance the food experience.

Trust your senses

The intricate association between aroma and flavor demands rigorous sensory analysis in order to determine what products will be acceptable to the consumer. "Sensory analysis is a critical step in innovation to give consumers the products they want, where, when and how they want them," says Jeffrey Kondo, vice president of product innovation for Dairy Management Inc./DMI (www.dairyinfo.com), Rosemont, Ill.

Aromas not only enhance flavor, they can enhance mood. Since the 1920s, scientists have noted powerful, mood-enhancing effects from such "comfort" aromas as cinnamon and clove.

DMI supports a pilot sensory lab at North Carolina State University's Southeast Dairy Foods Research Center, Raleigh, N.C. It is part of DMI's National Dairy Foods Research Center Program, a unified coordinated research effort designed to support and accelerate dairy innovation.

"Very important to industry are the sensory lexicons developed by MaryAnne Drake and her team," says Kondo. Drake is associate professor of sensory and flavor chemistry in the university's Department of Food Science. "These lexicons not only provide a standardized way of describing flavors but also link these flavors to chemical compounds. When you describe something as having a 'dairy flavor,' she's able to link that to at least some of the compounds that are actually causing that flavor. The descriptions and classifications can help a dairy processor keep going down the right road on a new product," explains Kondo.

Drake's approach to sensory analysis begins with her knowledge of the physiological ability to detect and distinguish aromas and flavors. "There are many modern instruments designed for sensory analysis, but nothing matches the human instrument for its complexity, intensity and sophistication of detection," says Drake. "Sensory testing is critical. Knowledge of consumer desires and perceptions and the sensory properties of existing competitor products can influence the breadth, depth and success of a product line. The dairy industry is in a desirable position in that its flavor and odor profiles are already pleasing to most consumers."

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"Aroma testing is always a challenge," says Kathleen Rutledge, founder of 21st Sensory Inc. (www.21stsensory.com), Bartlesville, Okla. "Ventilation issues are paramount to ensure the aroma from one product is not present when the next is evaluated. The objectives of the evaluation are important. For example, soy analogs can have a 'beany' aroma that does not elicit as much anticipatory interest as grilled beef. So a formulator can add smoke and some hydrolyzed vegetable protein or yeast ingredients to heighten the meat-like aromas.

"These compounds also can serve to mask any uncharacteristic aromas," continues Rutledge. "Often, the product developer submitting products for testing does not reveal what has been done to the product to increase or mask aroma. There is often a misguided idea that telling the testing group what the objectives are will bias the study. The opposite is true. With so many sensory signals being evaluated, the sensory group can benefit from being told the objectives and the work can be focused and the extraneous eliminated."

"The key for companies considering sensory testing is, what specific questions are you trying to answer? Do you want to understand the impact of substituting a new ingredient? Would you like to know how your product stacks up against a competitor's products? Different questions require different kinds of sensory testing, different objectives and different timelines," Drake adds.

Preserving the aroma

Given the nature of odor molecules - volitalized compounds - time is their natural enemy. Thus, reducing the rate at which aroma molecules evaporate protects the flavor and aroma of food.

"Acidulants are known to affect the rate of evaporation of various volatile ingredients," explains Barbara Heidolph, food marketing technical service and applications specialist for St. Louis-based ICL Performance Products LP (www.astaris.com). "Acidulants and acid salts can control the pH of a food or beverage via adjustment and buffering. Such acidulants and acid salts include the organic acids, such as adipic acid, citric acid and malic acid, or inorganic acids, such as phosphoric acid.

"Each acid has an ideal buffering range, so selection can be made based upon the target pH of the food product. Acid salts also may be used," she continues. "Monosodium phosphate is one of the best buffering agents available. When monosodium phosphate and disodium phosphate are used in combination, they can target a specific pH and maintain it."

While ICL does not make products that enhance aromas in food, the company does make ingredients that may affect the rate of evaporation of various volatile compounds and aid in aroma stabilization, thereby controlling the aroma of the food. Their technical experts work with the formulators to aid in selection of the right ingredient for their application as well as assist in process design, materials of construction and packaging. Other functional ingredients that may aid in aroma enhancement include: sequestrants, enzymes and of course antioxidants.

"Antioxidants help to stabilize the food and prevent deleterious reactions including rancidity," adds Heidolph. "Acidulants and sequestrants act as synergist with most antioxidants by interacting with metal ions such as copper and iron, preventing them from inhibiting the antioxidant function. Additionally acids and acid salts supply the desired reducing environment of hydrogen ions that will aid in regeneration of antioxidants during the storage life of a food or beverage."

The aromas and flavors of many of natural processes can be captured through distillation, extraction and other methods and be concentrated for use in other formulations. For example, Mastertaste's Zesti-Smoke line captures the flavor, aroma and even appearance of a traditional meat-smoking process by condensing natural wood smoke vapor with water," says Mastertaste's Manheimer. "Natural isolates, essential oils and oleoresins can help contribute to the consumer's experience."

This can be used in sauce and marinade applications to give the consumer the same experience they might have with a product that had been traditionally smoked.

"Aroma and flavor go hand in hand, just as you would see in any natural food process," says Manheimer. "Smoking meats will give the end product a specific aroma and flavor. Another example is the concentration of aromas from juices like citrus and apple, which possess a different distinct aroma and flavor."

Effective use of natural aromas is more than a mere mixing of chemicals because the intricate association between taste and aroma goes beyond simple chemical detection. We're accustomed to certain tastes and odors accompanying one another and can be put off by what are perceived as incongruent mixes.

Aroma and taste are inseparable qualities of food; altering one influences the other. This influence requires the most stringent of testing techniques that utilize the most sophisticated of instruments   the human instrument, the one owned by each consumer.