Sweetness and Sweeteners - American Chemical Society

Chapter 27 Improving the Taste of Artificial Sweeteners Using Flavors 1

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Downloaded by UNIV OF OKLAHOMA on September 8, 2013 | http://pubs.acs.org Publication Date: March 4, 2008 | doi: 10.1021/bk-2008-0979.ch027

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Masashi Ishikawa , Akio Nakamura ,* Ayano Fujiki , Junichi Ide , and Kensaku Mori 2

Technical Research Center, T. Hasegawa Company, Ltd., 335 Kariyado, Nakahara-ku, Kawasaki 211-0022, Japan Department of Physiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan

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Aiming to create flavorings that would bring the taste of artificial sweeteners closer to that of preferred sugar, we used multi-channel near-infrared spectroscopy (NIRS) to measure cortical responses coupled with sensory evaluation. As a result, it was noted that a conditional sugar solution reduced the amplitude of the response to the test sugar or artificial sweetener solution. In other words, the cortical response to a test solution was found to show adaptation by the conditional sugar solution. Sugar-sugar self adaptation was significantly greater than sugar-artificial sweetener cross adaptation recorded at specific regions of the temporal and frontal cortex. The sugar-artificial sweetener difference in taste could thus be monitored by the difference in cortical responses. Furthermore, sugar-flavored artificial sweetener cross adaptation tended to come close to sugar-sugar self adaptation among the subjects who sensed improvement of the taste of an artificial sweetener by addition of a particular flavoring.

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© 2008 American Chemical Society

In Sweetness and Sweeteners; Weerasinghe, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.


421 In response to recent, markedly growing consumer demand for lowcalorie/sugar-free food products containing non-nutritive artificial sweeteners, such sweeteners have become increasingly used as sugar substitutes (/). However, it has been known for some time that despite improvement these sweeteners when compared to the preferred taste of sugar still differ in taste (2,3). This difference likely comes from complex multi-sensory modalities. For example, bitterness comes from gustatory modality (4). Astringency and the aftertaste might come from somatosensory modality. Flavor is also an important factor to differentiate the taste of artificial sweeteners from that of sugar. Commercial granulated sugar has its specific and preferred taste and odor. Artificial sweeteners do not possess such sugar-like flavor. Here, our attention is focused on the importance of olfactory modality in sensing sugar flavor. We have sought to improve the taste of artificial sweeteners by applying sugar flavorings, because of the continuing preference of many consumers for the taste of sugar. We hypothesized that adding particular flavorings might reduce the sugar vs. artificial sweetener difference in teste and thereby improve the taste of artificial sweeteners. In order to evaluate the improvement and the difference in taste, we have used two methods. The first method is by subjective sensory evaluation with the second method being by optical imaging of cortical responses to sweeteners using near-infrared spectroscopy (NIRS). NIRS is a non-invasive optical technique that continuously monitors cerebral hemodynamics (5) for the assessment of functional activity in the human brain (6-11). Although NIRS measurements are limited to the cortical surface, changes in the concentration o f oxygenated and deoxygenated hemoglobin in the cerebral vessels can be measured and taken as indicators for cortical activation. In the current study, using multi-channel NIRS, we sought to monitor cortical activity during the sensory evaluation. Our first objective was to detect the difference between cortical responses to sugar and artificial sweeteners using the optical imaging method. Our second objective was to create flavorings that would minimize the sugar vs. artificial sweetener difference in cortical responses and also minimize the difference found by the sensory evaluation.

Materials and Methods Subjects Twenty-four healthy volunteers (fifteen male and nine female, mean age 35.6 ± 8.3 years) participated in this study for three straight days. Written informed consent was obtained after a complete explanation of the study. To avoid any influence of environmental stress, each subject was seated comfortably


422 in a temperature, humidity, and brightness controlled room throughout the experiments.


Optical Imaging Optical imaging was conducted with the ETG-4000 Optical Topography System (Hitachi Medical Co., Japan) using a 3 χ 11 optode set (consisting of 16 photo-detectors and 17 light emitters) providing a total of 52-channels. Nearinfrared laser diodes with two wavelengths (695 and 830 nm) were used as light emitters. Reflected lights were received by photo-detectors located 30 mm from the emitters. The optodes, which were mounted on a flexible cap, were carefully positioned on each subject's head so that the position was similar for all subjects. This configuration thus enabled us to detect signals simultaneously from the 52channels which covered a 60 χ 300 mm frontal area of the cortex in both hemispheres. Signals reflecting the relative oxygenated hemoglobin concentration ([oxyHb]), deoxygenated hemoglobin concentration ([deoxyHb]) changes were recorded from a starting baseline. 2

Procedure In this experiment, a high sweetness sugar substitute such as aspartame was used for the artificial sweetener solution. The de^ee of sweetness was converted to sugar equivalence. Ten mL granulated sugar (6%) for the sugar solution, aspartame (0.036%), or flavored aspartame solution was given to subjects as a test sample using a disposable cup with a straw. The flavorings contained volatile compounds from which subjects sensed granulated sugar-like sweet odor, based on analysis of raw cane sugar aroma constituents (12). Before measurement, subjects were trained to retain in mind taste characteristics of a sugar solution and that of an artificial sweetener solution. Test samples were given to the subjects one by one. After the optodes were placed on the subject's head, the subject was ready to start the sensory evaluation task. At time 0, we asked the resting subject to start the task. The subject would then pick up the cup and after a few seconds start to drink the given sample solution, then put back the cup on the desk. The subject would finish drinking by 5 seconds after the starting each, then concentrate on the sensory evaluation. After each task, the subject filled out a sensory evaluation questionnaire, comparing test samples and the corresponding conditional sugar solution. Five descriptors were used, namely, sweetness, odor, bitterness/astringency, sweetness aftertaste, and bitterness aftertaste, with each being rate on a scale ranking from -3, indicating "much weaker" to +3, indicating "much stronger", with 0 as the same when compared to the conditioning.


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Results and Discussion


Optical Imaging of Cortical Responses When subjects tasted a sugar or an artificial sweetener solution, a distinctive increase in [oxyHb] and a decrease in [deoxyHb] were observed in specific regions of the frontal and temporal cortices. The intensity of the changes were maximum in the temporal portion of the measurable area in both left and right cortical regions with the middle area showing no clear increase and decrease. The left half of Figure 1 shows the time course of typical changes in [oxyHb] evoked by the sensory evaluation task. [OxyHb] increased to a maximum level with a peak latency at about 25 seconds, then gradually returned to the baseline. Among the twenty-four subjects examined, such clear and robust increases in [oxyHb] were observed in fourteen subjects (58%). However, the remaining ten subjects showed little or no responses. To further assess the difference in cortical responses to sweetener solutions, we concentrated on analysis of such clear changes in [oxyHb] as cortical responses obtained from the fourteen subjects. The fourteen subjects showed such cortical responses to sugar and aspartame, regions evoked by the drinking of an aspartame solution being quite similar to those evoked by a sugar solution. As a first step, we addressed the question whether the amplitude of the cortical responses differ between a sugar solution and an artificial sweetener solution. Systematic analysis of the cortical responses in the fourteen subjects showed, however, that there are no statistically significant difference in the amplitude of the cortical responses between sugar and aspartame. Furthermore, a subject showed a greater response to aspartame in one experiment, whereas in smother experiment the same subject showed a greater response to sugar. In these experiments, we measured cortical responses to sugar, aspartame, and flavored aspartame in a sequential manner. Therefore, we thought that an amplitude of the cortical response to a sample was influenced by the previous response.

Self Adaptation and Cross Adaptation of Cortical Responses When a subject drank a sugar solution, then after 60 seconds drank a second sugar solution, a significant reduction of the amplitude of the second response was noted. The amplitude of the response to the test sugar solution was apparently influenced by the previous response to the conditional sugar solution as shown in Figure 1. This is a self adaptation of cortical responses to sugar solutions. When the test solution was changed to aspartame, we noted that the conditional sugar solution also reduced the amplitude of the response to the test aspartame solution. This is a cross adaptation of cortical responses to sugar-


424 aspartame solutions. In other words, the cortical response to an aspartame solution showed cross adaptation by the conditional sugar solution. It can be noticed that the sugar-aspartame reduction was smaller than the sugar-sugar reduction as shown in Figure I. This raised the possibility that sugar-sugar self adaptation might be greater than sugar-aspartame cross adaptation of cortical responses.


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Figure 1. Typical cortical responses to conditional sugar-test sugar solutions and conditional sugar-test aspartame solutions.

If this is the case, the comparison between cross and self adaptation could be a useful tool to evaluate the difference between cortical responses to sugar and artificial sweeteners. We thus addressed the question whether sugar-sugar self adaptation was greater than sugar-aspartame cross adaptation of cortical responses. In order to quantify these adaptations, the sugar solution was always given to subjects as a conditioning before every test sample solution. We then compared the ratio of adaptations between test samples by calculating the ratio of the amplitudes of responses to test samples and those of the previous responses to the conditioning. In order to avoid order effect within one day, we compared the cortical responses to the first pair of conditioning and test solutions, although the measurement of the cortical responses to the conditioning and test solutions were repeated four times in one day.


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Comparison between Self Adaptation and Cross Adaptation Figure 2 shows a comparison between sugar-sugar self adaptation and sugaraspartame cross adaptation recorded at a specific region (channel 41, C H 41). In the fourteen subjects, twelve subjects showed clear and robust responses in this region. Therefore, we compared the ratio of adaptations in these twelve subjects. O f the twelve, in ten subjects (83%), sugar-sugar self adaptation was greater than sugar-aspartame cross adaptation, mid the opposite results were noted in the remaining two subjects. Statistical analysis indicated that sugar-sugar self adaptation was significantly greater than sugar-aspartame cross adaptation in C H 41 (P=0.012, paired Mest). These findings support the hypothesis that sugarsugar self adaptation is greater than sugar-aspartame cross adaptation of cortical responses. The solid circle in Figure 3 indicates the cortical region ( C H 41), where we observed larger sugar-sugar self adaptation as compared to the sugar-aspartame cross adaptation. Also in the surrounding regions of the left side of the brain and in some regions of the right side (dotted areas in Figure 3), sugar-sugar self adaptation tended to be greater than sugar-aspartame cross adaptation. However the level of statistical significance was lower than that of C H 41 (0.05

Sweetness and Sweeteners - American Chemical Society

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