3.6 The "Melody" of Coffee
• Salivary
FOOD
PROPERTIES
33
• Aroma compounds
• Taste compounds
• Texture
• Color IN-MOUTH ENVIRONMENT
• Appearance
• Breathing
• Mastication
• Swallowing
• Mucous layer
PSYCHO-SOCIAL
EFFECTS
• Culture
• Memories
• Expectations
• Mood
• Alertness
. Attention
Fig. 3.1 Three factors influence flavour perception. The first includes all aspects that are related solely to the food, such as the aroma-active compounds present and interactions between the food matrix and aroma compounds. The second comprises all aspects related to the in-mouth situation. This makes the person eating the food an integral part of the system being analysed, and takes account of interactions between food and consumer. Finally, psychosocial and cognitive effects modulate aroma perception
Coffee is an interesting example of olfactory preference. The remarkable preference that some consumers develop for the volatile aroma molecules liberated from mature, partially fermented, dried, roasted and ground beans of the plant are testament to the integrative nature of the olfactory preference development process. The positive preferences that are developed are presumably a consequence, in part, of neurophysiological inputs from caffeine rather than nutritive or even microfloral inputs. Coffee aroma evolves in the mouth during drinking and finishes over several minutes after swallowing, with a typical after odour in the mouth. The nose space technique is able to capture many of these dynamic processes analytically, and gives a vivid insight into aroma release and its temporal evolution in the mouth. An abbreviated selection of I I compounds that were simultaneously measured in the air exhaled through the nose during drinking of espresso coffee is shown (Fig. 3.2) using a technique termed proton-transfer reaction mass spectrometry (PTR-MS) [26, 27]. The top-left frame of Fig. 3.2 shows the in-mouth temperature measured with a tiny thermocouple in the coffee assessor's mouth. Prior to taking coffee into the mouth, the temperature was about 35 oc. As the individual sipped the coffee (at 50 s), the temperature rose immediately to 46 oc, and then decreased owing to the thermal conduction in
in the oral cavity. After keeping the coffee in the mouth for 10 s, the temperature dropped below 40 oc. In this specific aroma evaluation, the individual assessor was instructed to keep the coffee within the mouth for a relatively long time prior
to swallowing in order to extend the measurements during the basic processes that occur in mouth. The concentration-time plots are those of compounds appearing at the indicated masses (m/z) in the nose space air: m/z 37 corresponds to the protonated water cluster, H20•H30+, present in the breath air, whether or not the person had coffee in the mouth (natural humidity in breath). This water signal acts as a marker for the regularity and stability of breathing rhythm, another important variable in the overall in-mouth experience. Though some- what arbitrary, the overall aroma development can be considered sequentially in stages. First, at the first contact of the liquid coffee with the in-mouth environment, there is an initial rise in the concentration of aromatic compounds, the first-sip aroma. Second, the concentration of the various compounds avail- able to the olfactory epithelia peaks and then decreases rapidly. Breaking these individual compounds into discrete temporal curves of concentration versus time reveals that the rate of decrease is not the same for all compounds; hence, the overall profile of the coffee aroma exposed to the olfactory epithelia, again, changes with time. The rapid decrease of the concentrations of volatile com- pounds from coffee in the breath air is believed to be a combination of various phenomena: (l) temperature dependence of the air—water partition coefficient,
(2) dilution of coffee with saliva, (3) interaction with saliva constituents and (4) adsorption and diffusion into the mucous layer. Third, when coffee is swallowed, coffee volatiles are released during the passage through the throat. The subsequent exhalation, the swallow-breath, entrains these volatiles through the nose and out through the nostrils. Accordingly, the corresponding aroma profile is called the swallow-breath aroma. For a series of compounds, high concentrations of volatiles are measured in the breath air just after swallowing. Fourth, when coffee is swallowed, the breath air continues to contain some of the coffee volatiles for several more minutes. This effect is known as the finishing or after- odour aroma. The persistence of various coffee aroma compounds in the breath air is reminiscent of coffee aroma, although it has a composition quite different from the aroma in the first sip, or the swallow breath. The breath-by-breath observations of the retronasal aroma transport of a wide variety of subjects revealed inter- and intraindividual differences and documented the need to go beyond a static aroma description. Simply describing the odorant exposure experience requires that the various compounds be measured
odorant exposure experience requires that the various compounds bc measured as an integrated and dynamic process, but the differences among subjects imply that additionally an individualised view be brought into the very first stages of flavour research—measurement of aroma exposure. The breakthroughs in meth- odologies that bring such analytical precision to studying olfactory exposure can now be brought to address a more concrete understanding of the customerk perception of food aroma in general. The analytical approaches described must now be coupled to means to evaluate the subjective aspects of flavour preference simultaneous with odorant exposure. Ultimately, studies such as the evaluation presented will enable research to acquire a better understanding of how aromas lead to preferences for specific foods. The example of coffee aroma measurement revealed inter individual differences in the manipulation of the odorant exposure related to flavour preferences. That is, individuals who reported a greater preference for coffee manipulated the concentration of aromas to increase the net concentration and duration of exposure relative to individuals who did not regularly consume coffee. These approaches were thus capable of resolving novel aspects of the variation in individual consumers. For example, coffee is prepared differently from country to country. Individual preferences, modes of preparations and serving temperatures vary within a country and even within a family. Very accurate measures are necessary to resolve these subtle differences that are nonetheless critical to preference development. Recent studies have investigated the retronasal aroma from other foods such as ice cream or banana 1281. In all of these studies, a dynamic evolution was observed that was characteristic for the type of food and consumption temperature, and that revealed inter-individual differences. With methods in place to measure volatile aroma compounds within the ol- factory space of individuals in real time, and to couple these to subjective reports of preference, it then becomes possible to combine these with more comprehensive measures of acute metabolism and physiology within an individual during the period when a novel food is being first perceived and olfactory preferences
• Salivary
FOOD
PROPERTIES
33
• Aroma compounds
• Taste compounds
• Texture
• Color IN-MOUTH ENVIRONMENT
• Appearance
• Breathing
• Mastication
• Swallowing
• Mucous layer
PSYCHO-SOCIAL
EFFECTS
• Culture
• Memories
• Expectations
• Mood
• Alertness
. Attention
Fig. 3.1 Three factors influence flavour perception. The first includes all aspects that are related solely to the food, such as the aroma-active compounds present and interactions between the food matrix and aroma compounds. The second comprises all aspects related to the in-mouth situation. This makes the person eating the food an integral part of the system being analysed, and takes account of interactions between food and consumer. Finally, psychosocial and cognitive effects modulate aroma perception
Coffee is an interesting example of olfactory preference. The remarkable preference that some consumers develop for the volatile aroma molecules liberated from mature, partially fermented, dried, roasted and ground beans of the plant are testament to the integrative nature of the olfactory preference development process. The positive preferences that are developed are presumably a consequence, in part, of neurophysiological inputs from caffeine rather than nutritive or even microfloral inputs. Coffee aroma evolves in the mouth during drinking and finishes over several minutes after swallowing, with a typical after odour in the mouth. The nose space technique is able to capture many of these dynamic processes analytically, and gives a vivid insight into aroma release and its temporal evolution in the mouth. An abbreviated selection of I I compounds that were simultaneously measured in the air exhaled through the nose during drinking of espresso coffee is shown (Fig. 3.2) using a technique termed proton-transfer reaction mass spectrometry (PTR-MS) [26, 27]. The top-left frame of Fig. 3.2 shows the in-mouth temperature measured with a tiny thermocouple in the coffee assessor's mouth. Prior to taking coffee into the mouth, the temperature was about 35 oc. As the individual sipped the coffee (at 50 s), the temperature rose immediately to 46 oc, and then decreased owing to the thermal conduction in
in the oral cavity. After keeping the coffee in the mouth for 10 s, the temperature dropped below 40 oc. In this specific aroma evaluation, the individual assessor was instructed to keep the coffee within the mouth for a relatively long time prior
to swallowing in order to extend the measurements during the basic processes that occur in mouth. The concentration-time plots are those of compounds appearing at the indicated masses (m/z) in the nose space air: m/z 37 corresponds to the protonated water cluster, H20•H30+, present in the breath air, whether or not the person had coffee in the mouth (natural humidity in breath). This water signal acts as a marker for the regularity and stability of breathing rhythm, another important variable in the overall in-mouth experience. Though some- what arbitrary, the overall aroma development can be considered sequentially in stages. First, at the first contact of the liquid coffee with the in-mouth environment, there is an initial rise in the concentration of aromatic compounds, the first-sip aroma. Second, the concentration of the various compounds avail- able to the olfactory epithelia peaks and then decreases rapidly. Breaking these individual compounds into discrete temporal curves of concentration versus time reveals that the rate of decrease is not the same for all compounds; hence, the overall profile of the coffee aroma exposed to the olfactory epithelia, again, changes with time. The rapid decrease of the concentrations of volatile com- pounds from coffee in the breath air is believed to be a combination of various phenomena: (l) temperature dependence of the air—water partition coefficient,
(2) dilution of coffee with saliva, (3) interaction with saliva constituents and (4) adsorption and diffusion into the mucous layer. Third, when coffee is swallowed, coffee volatiles are released during the passage through the throat. The subsequent exhalation, the swallow-breath, entrains these volatiles through the nose and out through the nostrils. Accordingly, the corresponding aroma profile is called the swallow-breath aroma. For a series of compounds, high concentrations of volatiles are measured in the breath air just after swallowing. Fourth, when coffee is swallowed, the breath air continues to contain some of the coffee volatiles for several more minutes. This effect is known as the finishing or after- odour aroma. The persistence of various coffee aroma compounds in the breath air is reminiscent of coffee aroma, although it has a composition quite different from the aroma in the first sip, or the swallow breath. The breath-by-breath observations of the retronasal aroma transport of a wide variety of subjects revealed inter- and intraindividual differences and documented the need to go beyond a static aroma description. Simply describing the odorant exposure experience requires that the various compounds be measured
odorant exposure experience requires that the various compounds bc measured as an integrated and dynamic process, but the differences among subjects imply that additionally an individualised view be brought into the very first stages of flavour research—measurement of aroma exposure. The breakthroughs in meth- odologies that bring such analytical precision to studying olfactory exposure can now be brought to address a more concrete understanding of the customerk perception of food aroma in general. The analytical approaches described must now be coupled to means to evaluate the subjective aspects of flavour preference simultaneous with odorant exposure. Ultimately, studies such as the evaluation presented will enable research to acquire a better understanding of how aromas lead to preferences for specific foods. The example of coffee aroma measurement revealed inter individual differences in the manipulation of the odorant exposure related to flavour preferences. That is, individuals who reported a greater preference for coffee manipulated the concentration of aromas to increase the net concentration and duration of exposure relative to individuals who did not regularly consume coffee. These approaches were thus capable of resolving novel aspects of the variation in individual consumers. For example, coffee is prepared differently from country to country. Individual preferences, modes of preparations and serving temperatures vary within a country and even within a family. Very accurate measures are necessary to resolve these subtle differences that are nonetheless critical to preference development. Recent studies have investigated the retronasal aroma from other foods such as ice cream or banana 1281. In all of these studies, a dynamic evolution was observed that was characteristic for the type of food and consumption temperature, and that revealed inter-individual differences. With methods in place to measure volatile aroma compounds within the ol- factory space of individuals in real time, and to couple these to subjective reports of preference, it then becomes possible to combine these with more comprehensive measures of acute metabolism and physiology within an individual during the period when a novel food is being first perceived and olfactory preferences
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