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Aroma cognition.

The aromatic fragrance of coffee is the determination of its commercial value. What is the pathway of that aroma from the cup or container to the brain center that evaluates this property? And could a better understanding of this travel path lead to a higher quality product?

The vapor developed during roasting is a highly complex gas mixture containing several hundred already identified components with possibly an equal number not yet defined. Many of these components are insignificant odor-wise as they may be relatively odorless or contribute little to the overall bouquet. Some may be important as carriers for the more characteristic coffee notes. Some may be necessary as reinforcing agents for total aroma. Some may serve as blending agents. There are probably only a dozen or so specific ingredients in particular proportions that go to make up the desired effect. Occasionally, a foreign note may intervene to reduce the value of the cup.

The public recognizes all these hundreds of gaseous components as a single ambrosia. Trained coffee buyers evaluate the total coffee bouquet as well as specific notes in each total that add or detract value. They also appreciate the variability; depending on degree of roast. A light roast has a lesser amount of gaseous aroma factors with a residual green note; while a heavy dark roast can destroy some of the desirable scents, substituting charred empyreumatic flavors which are preferred in warmer climates. Practically none of these individual odors are present in the green state. All must be developed by critical thermal processing.

Fundamental studies of the mechanism whereby these coffee vapors reach the brain centers are underway and beginning to exhibit some small progress. However, studies on the evaluation of these vapors by the brain are still in a highly primitive state and await further efforts.

There are four separate and distinct unit operations in the transmission of odors to the brain: detection, processing, recognition, and evaluation.

Detection occurs in the nasal passages. The mouth, tongue, and palate are almost completely insensitive to aroma vapors. If the nose is held so no vapors can enter while chewing, an apple would taste about the same as an onion.

Within the nasal passages, there are some four million cells which are sensitive to various vapors. Until recently, we had no idea how these cells functioned. Now it has been discovered that these cells contain certain proteins that have the ability to combine with vapor components. This combination activates them, causing them to become electrically charged. The higher the concentration of aroma components, the higher the charge.

Transmission of these odor signals to the brain is thus strictly an electrical phenomenon. A bundle of nerve fibers carry the electrical charge from the nasal cells to a section of the brain long identified as the olfactory bulb. When this is deficient or missing, the sense of smell is lost.

The olfactory bulb does not identify odors. It integrates these electrical stimuli and disseminates them to other areas in the brain - with special connections to areas involved in memory and emotion. In the memory section, they are compared to previous experience with these electrical impulses and identified. In the emotional areas, they are evaluated on the basis of pleasure and distaste. They may even initiate strong love-hate reactions evolving from previous conditioning.

It is relatively easy to visualize how the brain perceives variations in strength of a single flavor note. Modem instruments have no difficulty in measuring differentials of a millionth of an ampere or watt. The brain is an even more sensitive electrical measuring instrument and can detect deviations of electrical charges far smaller than this.

Visualizing how the nasal passages perceive and differentiate, thousands of various odors we encounter are much more difficult and complex. There are hundreds of flowers, each with a different essence; dozens of spice and food scents; to say nothing of the thousands of chemicals each with their own specific smell which may have different degrees of pleasantness and repulsiveness.

Studying odor detection, recent experimented work indicates that there is not a single protein, but a group of receptor proteins located in the nasal cells. These have different faculties for combining with minute quantities of various odorants and becoming electrically charged to varying degrees. In this manner, they differentiate between hundreds of thousands of odors.

An analogy would be the method we detect color. The eye has only three different receptor proteins for the primary colors; red, blue, and yellow. Yet the eye can discriminate thousands of color shades and strengths by minute shifts in the relative signal power from each of these three classes of receptors.

Odors are far more complicate, than colors. Despite many attempts, we have as yet been unable to divide them into primary classifications as we have with colors. Still, we might postulate a dozen or so smell receptors, each sensitive to a particular category of odors. Each smell might stimulate the receptors into a characteristic pattern. Thus, coffee aroma might stimulate receptors two and five; and fail to affect one and seven, while it influenced others to different degrees.

Each aroma would then have its own characteristic olfactory profile, expressed as a range of amplitudes across the receptor field. The brain could recognize each odor by its pattern of receptor stimulation, creating an infinite number of combinations. Some receptors could have the ability to modulate the system, turning it up or down, m or off. This model may be pure conjecture, but many odor phenomena have been observed that can be explained by such an olfactory code. It may be the explanation of why some molecules are able to block or promote the perception of other odors.

This code could indicate a promising direction for future coffee aroma research. In cooperation with the green coffee buyer, chemists and psychologists might endeavor to discover which of the coffee odor components produce pleasant and attractive brain images (which stimulate the appetite and which turn it off). Optimum range for crucial aroma components could be established. Eventually blending could be computerized.

In addition, there could be other components that might well enhance coffee aroma. For example, it has been demonstrated that if a component of rose oil is incorporated into tomato juice, it causes the juice to blossom with a far greater tomato smell.

Odor cognition research may appear highly theoretical today. Tomorrow, it could revolutionize the industry by creating a superior aroma, with greater retention in the cup.
COPYRIGHT 1993 Lockwood Trade Journal Co., Inc.
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Coffee Break with Dr. Samuel Lee
Author:Lee, Samuel
Publication:Tea & Coffee Trade Journal
Article Type:Column
Date:Apr 1, 1993
Words:1077
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