Real-Time Flavor Release from Foods during Eating - ACS Publications

Chapter 3

Real-Time Flavor Release from Foods during Eating 1

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B. A. Harvey , M . S. Brauss , Rob S. T. Linforth , and Andrew J. Taylor

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Corporate R&D Division, Firmenich S. Α., 1 route des Jeunes, 1211 Geneva 8, Switzerland Samworth Flavour Laboratory, Division of Food Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, United Kingdom

Downloaded by INDIANA UNIV BLOOMINGTON on May 9, 2015 | http://pubs.acs.org Publication Date: September 7, 2000 | doi: 10.1021/bk-2000-0763.ch003

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Measurement of flavor release from foods as they are eaten on a breath-by-breath basis (nosespace) has been made possible using Atmospheric Pressure Chemical Ionization (APCI) Mass Spectrometry. A n overview is given of some applications of the technique, which is rapid, sensitive and quantitative. In conjunction with simultaneous sensory evaluation it may be used to assist in the design of release profiles of flavors from foods with desired perceptual characteristics; encapsulation of flavors added to chewing gum is used as an example. Change in nosespace volatile concentrations following homogenization of components of a composite food is demonstrated. The effects on flavor release of food formulation variables can be rapidly determined, illustrated by differential intensities and release rates from yogurts of varying fat content. A further example is given showing the sequential release during eating of enzymatically generated volatiles from fruit such as tomatoes.

It has long been a goal of flavor research to have an analytical procedure which could detect and discriminate odor chemicals from breath in real time with sensitivity comparable to the human nose. This has been achieved by Prof. A . Taylor and Dr. R. Linforth at the University of Nottingham in a joint project with Firmenich S.A.(7). The method used is Atmospheric Pressure Chemical Ionization (APCI) Mass Spectrometry, combined with a specially developed interface to allow continuous analysis of the breath from the nose (nosespace) of a volunteer taster. Breath is sampled at a constant rate and is diluted by a flow of nitrogen carrier gas. A P C I is a soft ionization technique, typically producing an ion of a flavor molecule plus a

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© 2000 American Chemical Society

In Flavor Release; Roberts, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.


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proton (MH+) without fragmentation. Many compounds may be monitored simultaneously in exhaled breath on a breath-by-breath basis and are identified by their different masses. Quantification is achieved by injection of standard solutions of volatiles in an effectively inert solvent, via a syringe pump into the carrier gas flow. Tests on a range of compounds of different functionalities have shown a linear response from the mass spectrometer over ranges of nosespace volatile concentrations commonly found during eating. APCI-MS as a technique for breath analysis has been reported elsewhere (2) although it is difficult to make a comparison of the relative performance. The use of A P C I - M S has opened up a great potential for analysis of gas phase volatiles in real time other than breath analysis. A range of such applications has been developed by Firmenich using the technique under the acronym AFFIRM® (Analysis of Flavors and Fragrances In Real-tiMe). Breath analysis however remains the most important application. The main advantages of AFFIRM® are the capacity to measure quantitatively the kinetics of the release of flavor molecules over much shorter time periods than has previously been possible, speed of data collection and sensitivity typically down to levels of a few ppb. This paper gives an overview of some applications of AFFIRM®ative nosespace analysis using a range of food types as examples.

Results and Discussion Data from breath analysis using AFFIRM® can be used in many ways. For instance, nosespace data can be collected from trained sensory panelists as they simultaneously estimate perceived flavor intensity as a function of time. Parallel processing of the analytical and sensory data obtained in this way can lead to a better understanding of those factors which affect flavor perception (3,4). AFFIRM® can be used to aid flavorists in flavor creation by matching nosespace concentrations of volatiles in a flavor formula incorporated in a food to those in a target food. It can, in addition, provide rapid feedback to flavorists and scientists in the development of e.g. flavor encapsulation systems. The speed of data collection also lends itself to initial screening of products before commencing sensory testing, with substantial savings of time and resources. Chewing gum is a good medium for demonstrating and comparing release of volatiles into the breath, since a large part of the starting material remains in the mouth for as long as required. A survey of market chewing gums has shown that the intensity and time dependence of flavor release vary greatly (5), illustrated by the release of menthol from three market sugar-free peppermint chewing gum sticks from different manufacturers (Figure 1). Release of a single flavor compound only, menthol, is presented here for clarity. Samples were chewed by the same operator for 20 minutes. Each data point represents the maximum menthol intensity from one breath. Data were collected for the first 5 minutes and for periods of one minute each after 10 and 20 minutes to compare lastingness.



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While the matrix compositions of the market samples are unknown and variable, flavor bursts in the first 1-2 minutes of eating can often be associated with the presence of visible embedded granules or a hard sugar coating containing relatively high concentrations of volatiles which are released into the breath when crushed by chewing. Release profiles between individuals vary greatly owing to differences in physiological variables such as breathing rate, manner and rate of chewing, and rate of saliva production. Rates and intensities of volatile release depend also on the nature of the food matrix and physicochemical properties of the volatiles. The importance of this last factor is demonstrated in Figure 2, where the time dependence of release of a series of volatiles from gelatin/pectin gels of fixed matrix composition are compared. Each release curve is the mean of 5 replicates eaten by the same operator and normalized to the maximum intensity. There is considerable variation between the times to maximum intensity, T , of the different compounds. A continuous change in the relative concentrations of the different flavor compounds therefore takes place in the air passing over the olfactory receptors as the gel is eaten, which can be quantified. In conjunction with sensory evaluation, the real time capacity of AFFIRM® can thus lead to a better understanding of the way we appreciate the flavor of foods. In parallel with this approach, progress is being made in the development of predictive models of the release of volatiles into the breath during eating based on physicochemical properties of the volatiles (6). max

Modifying Flavor Release Profiles It is an increasingly important market requirement, that a new flavor for a particular product should make a specific perceptual impression, for instance a powerful initial impact. For a given tonality, there is limited scope to substitute flavor compounds in a liquid formula for others according to their release properties, and control of flavor release through modifications to the food matrix composition or texture is often impractical. One flexible way to achieve a required flavor impression is by encapsulation of liquid flavors in various supports such as the Flexarome® range of carbohydrate-based flavor delivery systems developed by Firmenich, which also provides benefits in flavor stability. The usual procedure in the development of a new flavor, involving feedback between flavorists and sensory panels, is time consuming. AFFIRM® can provide substantial time savings by initial product screening and, through an increasing understanding of how the kinetics of flavor release affects perception, desirable features can be identified from nosespace profiles. Research is in progress both at the University of Nottingham and in the Corporate R & D Division of Firmenich SA to understand better those aspects of flavor release which affect perception, by simultaneous nosespace measurement and time-intensity sensory estimation by a trained panel of perceived flavor intensity. One important discovery obtained using flavored gelatin gels of varying gelatin content was a good correlation between the initial gradient of the nosespace release profile



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Figure 1. Menthol release from market peppermint chewing gum stich'.

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Figure 2. Release in-nose of volatiles from flavored gelatin/pectin gels normalized to maximum intensities.

and the maximum perceived flavor intensity (3). The correlation between maximum nosespace intensity and maximum perceived flavor intensity was not good. A steep



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initial gradient in the nosespace profile is therefore more important than the absolute flavour dosage in achieving an intense flavor impact. In the following example, a new Tutti Frutti flavor with a strong initial impact was required for bubble gum. A liquid flavor was encapsulated into each of three Flexarome® products, differing only in the composition of the Flexarome® matrix. The flavor level in each Flexarome® product was measured and batches of bubble gum were made to the same formula containing each of the Flexarome® products at an equivalent flavor dosage. Release profiles of amyl valerate from the different bubble gum batches are compared during the first minute of eating in Figure 3. Each curve is the mean of 3 replicates eaten by the same operator.

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Time (min) Figure 3. Effect of encapsulation in Flexarome® matrices on the release of amyl valerate in-nose from tutti-frutti flavored bubble gum. The initial rate of change of amyl valerate concentration in the nosespace is many times greater from the bubble gum samples containing the Flexarome® products than from the sample containing the liquid flavour. This is because the carbohydrate matrices of the Flexarome® products provide a physical barrier restricting the rate of partitioning of amyl valerate into the gum base, a process which is thermodynamically favored by the hydrophobicity of both the gum base and amyl valerate. Other hydrophobic flavor compounds, notably limonene, showed similar differences in initial nosespace gradients between the bubble gum batches. The differences in release profiles of more hydrophilic flavor compounds between the bubble gum samples containing Flexarome® and that containing liquid flavor were less pronounced, as expected, but tasting confirmed the greater initial flavor impact from samples containing Flexarome®.


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The dependence of perceived flavor intensity on the rate of change of volatile concentration in the breath indicates that the optimum form for flavor release profiles over a period of time should be a series of spikes rather than a uniform level. This may be achieved using an appropriate mixture of encapsulants with different temporal flavor release characteristics. Figure 4 shows the mean of 3 replicates of menthone release from chewing gum eaten by the same operator. There are two distinct maxima, within the first minute and after about 1.7 minutes of eating, which result from formulating in a single chewing gum batch menthone encapsulated in two different matrices with clearly differentiated time release properties.

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Time (min) Figure 4. Release in-nose of menthone encapsulated in two different matrices from sugar free chewing gum. When incorporated in a given food matrix, encapsulation in Flexarome® matrices of single flavor compounds (or groups of compounds giving rise to different notes or tonalities) with different time release characteristics can provide great flexibility in the design of temporal flavor impressions.

Integrity of Components in Composite Foods and Flavor Release It is common experience that the flavor of foods composed of physically distinct components is adversely affected by homogenization. The components of composite foods typically differ in perceived taste, texture/mouthfeel and qualitatively in the volatiles released during eating. These are generally recognised by food scientists as the main factors contributing to flavor (7). If, for example, a plateful of freshly cooked fish, tartare sauce and French fries is mixed in a blender, few would disagree that the result was less palatable although the nutritional content was unaltered. However such a perceptual deterioration is not due solely to less desirable textural


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and mouthfeel qualities; A F F I R M ative nosespace analysis has shown in a number of such multi-component foods that substantial quantitative changes in volatile concentrations in-nose contribute to the deterioration in perceived flavor quality following homogenization. The approach with complex foods is firstly to obtain a mass spectrum of the headspace of each component of the food. It is then usually possible to identify one or more peaks of significant intensity at particular mass/charge ratios which are unique to that component. The chosen peaks are then monitored as the food is eaten in its usual form and when modified. It is not necessary to identify the peaks followed to observe the effect, although identification may be readily made in a preliminary step in which volatiles in the headspace of each component are trapped on Tenax, desorbed and subjected to G C - M S analysis. Figure 5 shows an example of peanut butter and concord grape jelly sandwiches, in which the raw chromatograms of a single peak from each component are presented with a common time axis. The signal in the upper channel originates only from the grape jelly and that in the lower channel only from the peanut butter. N o signal from either channel was recorded when the bread was eaten alone.

Figure 5. Release of marker volatiles in-nose from sandwiches containing peanut butter (lower channel) and grape jelly (upper channel) as discrete layers (starting at 73.5 and 76.5 minutes) and after homogenization (starting at 80.5 minutes).



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At an indicated time of 73.5 minutes, an operator ate a sandwich containing a thin layer of peanut butter topped with a thicker layer of grape jelly. A second sandwich containing a thicker layer of peanut butter, of the same weight (10 g) as the grape jelly, was eaten by the same operator at 76.5 minutes, and at 80.5 minutes a further sandwich was eaten containing 10g grape jelly and 10 g peanut butter which had been previously mixed in a food blender. The intensity of the signal from the grape jelly is clearly reduced when blended with peanut butter. The same effect was seen when sandwiches of the three compositions were eaten by two other operators. Greater exposure of volatiles from grape jelly to the high fat content of the peanut butter in the sandwich with the blended filling may reduce both their mass transfer rates within the food and lower air/food partition coefficients.

Fat Levels in Yogurt and Flavor Release The effect of fat levels on volatile release has been investigated in some detail using AFFIRM®, particularly from cookies and from yogurt. Many physical properties of food including texture/mouthfeel and melting profile depend on fat levels. Volatile release can depend on such factors through modified mass transfer rates within the food. Fat also has an important role as a reservoir for flavor molecules, which will partition between the fat, water and air phases according to the hydrophobicity of the flavor molecules. Thus increasing the fat content in fat/water/air systems decreases the headspace concentration of hydrophobic flavor molecules which reside preferentially in the fat phase, while headspace concentrations of hydrophilic flavor compounds are affected little by fat content (8). Quantitative instrumental data on these effects in vivo are sparse; compositional changes have been measured from cheeses of different fat content (P) although no comment on rates of release was possible. Sensory studies have shown clear tendencies for more intense but more transient flavor release from fat-free foods than from the full fat products {10). The dependence of both intensities and rates of volatile release on the fat content of foods can be determined rapidly using AFFIRM®. Rates of release of anethole, a moderately hydrophobic flavor compound, are compared in Figure 6 from set yogurts of different fat content (11). The data are from 5 replicates eaten by the same operator. Intensities have been normalized to show more clearly the differences in release kinetics; maximum intensities were approximately four times higher from the 0% fat yogurt than from the 3.5% and 10% fat yogurts, which were of similar intensity to each other. The T value of the 0% fat yogurt was lower than those of the 3.5% and 10% fat yogurts and there is a trend of greater persistence with increasing fat content. The difference in T values between the 0% and 10% fat yogurts is statistically significant.

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Figure 6. Volatile release in-nose of anetholefromyogurts of different fat contents, normalized to maximum intensities. (Reproduced from reference 11. Copyright 1999 American Chemical Society.)

Time Dependence of Release of Enzymatically Generated Volatiles The short time resolution possible using AFFIRM®ative nosespace analysis renders it particularly suitable to study the temporal aspect of flavor release from fruits such as tomatoes from which both preformed and enzymatically generated flavor molecules are liberated during eating (72). Release of the two classes of volatiles are compared in Figure 7. Intensities have been normalized to the maxima and each curve represents the mean of 5 replicates eaten by the same operator. Isobutylthiazole is present in the intact tomato in the active form and is released first. Hexenal and hexenol are derived from linolenic acid by a sequence of enzymes in the lipid oxidation pathway. (Z)-3-hexenal is a product of the first enzymic step which can be followed by conversion to (£)-2-hexenal. As AFFIRM® cannot distinguish between isomers, the signal for hexenal in Figure 7 is the sum of the (2)-3 and (E)-2 isomers. A further enzyme step from either hexenal isomer can produce the corresponding hexenol isomer. Differences in T values between isobutylthiazole and hexenal, and between hexenal and hexenol, were statistically significant (p < 0.05, Student t-test). These T values agree with the enzymic pathway and sequence responsible for production of hexenal and hexenol. m a x

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Figure 7. Release in-nose of preformed and enzymatically generated volatiles from plum tomatoes. (Reproduced from reference 12. Copyright 1998 American Chemical Society.)

Conclusions The examples given demonstrate how AFFIRM®ative nosespace analysis provides a rapid method for the quantitative analysis in real time of volatiles in the breath during eating. The time resolution clearly distinguishes release rates during eating of different volatiles in a given food or of a given volatile as a function of composition variables such as fat levels in manufactured food. Combined with sensory analysis AFFIRM® is leading to a better understanding of those factors which affect flavor perception and is assisting in the design of flavor delivery systems. The speed of data collection and processing can offer substantial savings of resources in flavor development.

References 1.

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3. 4.

Linforth R.S.T.; Ingham K . E . ; Taylor A.J. In Flavour Science: Recent Developments; Taylor A.J.; Mottram D.S., Eds.; Royal Society of Chemistry: London, 1996, pp 361-368. De Kok P.M.T.; Smorenburg H.E. In Flavor Chemistry, Thirty Years of Progress; Teranishi R.; Wick E.L.; Hornstein I., Eds.; Kluwer Academic/Plenum Publishers, New York, 1999, pp 397-407. Baek I.; Linforth R.S.T.; Blake Α.; Taylor A.J. Chem. Senses. 1999, 24, 155-60. Linforth R.S.T.; Baek I.; Taylor A.J. Food Chem. 1999, 65, 77-83.


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5. 6.

Harvey B . A . Kennedy's Confection. May 1997, ppl8-20. Linforth R.S.T.; Friel E.N.; Taylor A.J. In Flavor Release: Linking Experiments, Theory and Reality; Roberts D.D.; Taylor A . J . , Eds., American Chemical Society: Washington D C , 1999. 7. Taylor A.J. Crit. Rev. Food Sci. Nutr. 1996, 36, 765-784. 8. De Roos K . B . Food Technol. 1997, 51, 60-62. 9. Delahunty C.M.; Piggott J.R.; Conner J.M.;Paterson A . Ital. J. Food Sci. 1996, 2, 89-98. 10. Bennet C.J. Cereal Foods World. 1992, 37, 429-432. 11. Brauss M . S . ; Linforth R.S.T.; Cayeux I.; Harvey B.A.; Taylor A.J. J. Agric. Food Chem. 1999, 47, 2055-2059. 12. Brauss M.S.; Linforth R.S.T.; Taylor A.J. J. Agric. Food Chem. 1998, 46, 22872292.


Real-Time Flavor Release from Foods during Eating - ACS Publications

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