2017 Volume 23 Issue 1 Pages 51-56
The aim of this study was to investigate the relationship between the influence of sweeteners on the in vivo aroma release from beverages and aroma perceptions. Equi-sweet and lemon-flavored model beverages were prepared using sucrose, acesulfame potassium (ACK), aspartame (ASP) and sucralose. The amounts of in-mouth odorants exhaled through the nostrils during the consumption of the model beverages were compared using the Retronasal Flavor Impression Screening System (R-FISS) by 4 trained panelists, and the relationship between the in vivo aroma release and their aroma perceptions was evaluated. As a result of the sensory evaluation using quantitative descriptive analysis, the lemon-like aroma of the beverage containing ACK was perceived to be significantly weaker, while the green aroma of the beverage containing sucralose and the spicy aroma of the beverages containing ASP and sucralose were perceived as significantly stronger than the other beverages. In contrast, there were no in-mouth odorants showing significant differences in their amounts that were common to the 4 panelists. Therefore, it was found that the sweeteners could have a small impact on the in vivo aroma release from the model beverages. These results suggested that differences in aroma quality of the model beverages by the types of sweeteners could result from factors other than the in vivo aroma release. Furthermore, it is highly likely that the taste-aroma interactions caused by the aroma and taste compounds would be one of the factors having a significant impact on the different aroma perceptions of the beverages containing the different sweeteners.
Flavor is considered to be a multi-modal sense resulting from multiple stimuli elicited by the aroma and taste compounds in foods, and is one of the most important characteristics determining the acceptance of foods by consumers. Recently, the increased consumer demand for healthier foods has resulted in a growing demand for low-calorie beverages with low-calorie sweeteners such as acesulfame potassium (ACK), aspartame (ASP) and sucralose. These artificial sweeteners have been widely used as alternatives to sugar in various beverages. In general, flavor perceptions of beverages can vary by the types of sweeteners. It was previously demonstrated that the intensity of the perceived flavor and overall aroma of beverages differed based on the types of sweeteners used in the beverage bases (Hewson et al., 2008; Matysiak et al., 1991; Wiseman and McDaniel, 1991). Previous studies have also reported that the amounts of aroma compounds released into the headspace of the beverages and their behavior varied by the types of sweeteners or their concentrations (Da Porto et al., 2006; Deibler and Acree, 2000; Hansson et al., 2001; King et al., 2006; Nahon et al., 1998; Rabe et al., 2003). Moreover, some of the studies indicated the possibility that the changes in the aroma perception could result from differences in aroma release from the beverages (Deibler and Acree, 2000; King et al., 2006; Nahon et al., 1998). These studies, however, investigated the influence of sweeteners on the in vitro aroma release from beverages using a model system such as a model mouth, etc°C, but the influence on the in vivo aroma release requires further explanation. Therefore, study of the influence of sweeteners on the in vivo aroma release from beverages would assist in understanding the relationship between beverage composition and the perception of aromas.
In this study, a Retronasal Flavor Impression Screening System (R-FISS; Kumazawa et al., 2008) was employed in order to examine the amounts and composition of the odorants exhaled through the nostrils via the nasal cavity. R-FISS is one of the analytical techniques used to analyze in-mouth odorants exhaled from the human nose. The major advantages of this technique are the ability to improve the detection limit of the odorants by concentrating them on a resin adsorbent and to determine the composition of the mixture consisting of a significant number of odorants in one measurement. Therefore, the aim of this study was to investigate the relationship between the influence of sweeteners on the in vivo aroma release from beverages and their aroma perception by comparing the amounts of the in-mouth odorants exhaled through the nostrils during the consumption of lemon-flavored model beverages containing different sweeteners.
Chemicals The following chemicals were purchased from the suppliers shown: the 11 odorants shown in Table 1 (Tokyo Chemical Industry Co., Ltd., Tokyo, Japan); 2-octanol and citric acid (Nacalai Tesque, Inc., Kyoto, Japan); sucrose, acesulfame potassium, aspartame, sucralose (Wako Pure Chemical Industries, Ltd., Osaka, Japan). The chemical purity of the 11 odorants shown in Table 1 and 2-octanol was confirmed by gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS).
| Compound | Conc. in ethanol (% w/w) | Selected ion (m/z)a | Response factorb | |
|---|---|---|---|---|
| cal. | ref. | |||
| α-pinene | 0.20 | 93 | 91 | 1.3 |
| camphene | 0.10 | 121 | 93 | 3.0 |
| myrcene | 0.10 | 69 | 93 | 1.7 |
| γ-terpinene | 0.80 | 136 | 121 | 3.3 |
| terpinolene | 0.20 | 121 | 93 | 2.1 |
| neral | 0.40c | 109 | 69 | 16.2 |
| geranial | 152 | 109 | 34.5 | |
| neryl acetate | 0.40 | 136 | 154 | 51.8 |
| geranyl acetate | 0.20 | 93 | 136 | 16.1 |
| nerol | 0.20 | 69 | 93 | 13.4 |
| geraniol | 0.40 | 69 | 136 | 8.3 |
Preparation of the Model Lemon Flavor The aroma composition of the model lemon flavor is shown in Table 1. The eleven odorants were dissolved in 99.5% ethanol.
Preparation of the Lemon-flavored Model Beverages The experimental design for the lemon-flavored model beverages is shown in Table 2. The model beverages were prepared so that the sweetness level of each model beverage containing the artificial sweeteners (beverages 2–4) was about the same as that of the beverage containing 4% sucrose (beverage 1). The equi-sweetness was determined by the sweetness power function for each sweetener based on experimental results from previous papers (Tornout et al., 1985; Wiet and Beyts, 1992). Their sweetness levels were then confirmed by sensory evaluation.
| Beverage number | Sucrose (% w/w) | Acesulfame K (ppm) | Aspartame (ppm) | Sucralose (ppm) | Citric acid (% w/w) | Lemon flavor (%v/v) |
|---|---|---|---|---|---|---|
| 1 | 4.0 | 0 | 0 | 0 | 0.1 | 0.1 |
| 2 | 0 | 200a | 0 | 0 | 0.1 | 0.1 |
| 3 | 0 | 0 | 200a | 0 | 0.1 | 0.1 |
| 4 | 0 | 0 | 0 | 60a | 0.1 | 0.1 |
First, the artificial sweeteners and citric acid were completely dissolved in distilled water at room temperature. The model lemon flavor was then added to each solution and mixed thoroughly in a sealed glass flask. The model beverages were immediately used (within 2 hours at the most) without sterilization after addition of the flavor.
Sensory Evaluation of the Model Beverages by Quantitative Description Analysis (QDA) Fifty grams of the model beverages was weighed into plastic cups, and then each cup was immediately capped with a plastic cap. These 4 model beverages were evaluated by 10 panelists (5 males and 5 females) employed by Ogawa & Co., Ltd. All the panelists had previously received extensive training in the descriptive sensory analysis of citrus-flavored beverages and had experience in the sensory profiling of various food samples. First, the panelists generated 17 aroma attributes by comparing the aroma profiles of each model beverage. These attributes were then ranked and clustered to determine the key attributes of the samples. Five key attributes were ultimately selected, and their definitions were confirmed by the panelists. Next, the 4 samples (beverages 1-4) were randomly presented to the panelists. Beverage 1 was also used as a control and was presented to panelists in addition to the 4 samples. The intensity of each attribute for the control was defined as 4. Ion exchanged water was provided for rinsing of the mouth. The panelists scored the intensity of each aroma quality for the 4 model beverages using a seven-point scale from 1 (very weak) to 7 (very strong) compared to that for the control. All samples were evaluated 3 times by each panelist. The sensory results were then analyzed using a one-way analysis of variance (ANOVA) followed by Tukey's test.
Trapping of In-mouth Odorants Exhaled through the Nostrils In order to determine the in-mouth odorants, the breath exhaled through the nostrils was trapped according to the procedure described in a previous paper (Itobe et al., 2009). After 30 mL of the model beverage at room temperature was placed in the mouth cavity, the panelists paused for 1–2 seconds, and then swallowed all of the liquid in one gulp. Ten breaths after the beverage had been swallowed were passed through a small glass column (6 cm × 5 mm i.d.) filled with Tenax TA (100 mg, 80/100 mesh, GL Science, Tokyo, Japan), which had been heated at 220°C for 2 hours prior to the analysis. The end of the glass column was connected to a pump by a silicon tube, and a suction of approximately 1 L/min was applied to the system during trapping of the air exhaled through the nostrils. This sampling system allowed the panelists to normally exhale without the need to press air through the Tenax column. After trapping of the in-mouth odorants, five microliters of an internal standard solution (5 µg/mL 2-octanol in ethanol) was directly added to the Tenax column for the quantitative analysis. The water and ethanol were then removed from the Tenax TA by flowing dry nitrogen (30 min, 100 mL/min). These experiments were carried out at room temperature (25°C ± 2°C). The experiments were performed by 4 trained panelists, and the Tenax columns were used as the samples for the GC-MS analysis. A blank test was also performed under the same conditions using distilled water.
GC-MS Thermal desorption of the trapped odorants on the Tenax column was performed with a TDU thermal desorption system (Gerstel GmbH, Mülheim an der Ruhr, Germany) in combination with the ATEX option of an MPS-2 autosampler and a CIS-4 injector (Gerstel GmbH) according to the following parameters. Thermal desorption was performed by programming the TDU from 20 to 280°C (held for 3 min) at the rate of 12°C/s in the splitless mode. Cryofocusing was performed with liquid nitrogen at −150°C. Injection was performed with the ramp of 12°C/s from −150 to 260°C (held for 3 min) in the splitless mode. The odorants were analyzed by an Agilent 6890 N gas chromatograph with an Agilent 5975 B series mass spectrometer (Agilent Technologies, Palo Alto, CA, USA). The column was a 30 m × 0.25 mm i.d. DB-WAX fused silica capillary (J&W Scientific, Folsom, CA, USA) with a film thickness of 0.25 µm. The oven temperature was programmed from 30°C (held for 3 min) to 120°C at the rate of 3°C/min, and then raised at the rate of 5°C/min to 230°C. The flow rate of the helium carrier gas was 1 mL/min. The mass spectrometer was used at an ionization voltage of 70 eV (EI) and operated in the selected ion monitoring and scan (SIM-SCAN) mode. The ion source and quadrupole temperatures were set at 230°C and 150°C, respectively. The selected ions listed in Table 1 and 45 for 2-octanol were monitored in the SIM mode. The quantitative amounts of the in-mouth odorants were determined by the internal standard method using a response factor. The response factors of 11 odorants in the model lemon flavor to 2-octanol (internal standard material) are shown in Table 1, and these response factors were calculated from the ratio of the selected ion peak area of each odorant to 2-octanol obtained by mass chromatography of a standard solution containing equal weights of odorants and 2-octanol. These selected ion peak areas were the mean values of triplicate results. The odorants were then quantitated as in-mouth odorants. The results were then analyzed using a one-way ANOVA followed by Tukey's test.
Identification of the odorants Each odorant was identified by comparing its Kovats GC retention index and mass spectrum to those of the reference compounds.
Influence of Sweeteners on Aroma Perceptions during Consumption of the Lemon-flavored Model Beverages In order to investigate the influence of the sweeteners on aroma perceptions during consumption of the beverages, the aroma profiles of the lemon-flavored model beverages (Table 2, beverages 1–4), which had equi-sweet levels and the same aroma content, were compared by sensory evaluation using QDA. As a result, the intensity of the lemon-like aroma of beverage 2 was significantly weaker, while the intensity of the green aroma of beverage 4 and the intensity of the spicy aroma of beverages 3 and 4 were significantly stronger than the other beverages (Fig. 1). It was previously reported that the intensity of the perceived flavor changed according to the types of sweeteners and their concentrations in the citrus-flavored model beverages (Hewson et al., 2008). The present results demonstrated that the aroma quality and flavor intensity of the beverages were perceived to differ due to the types of sweeteners.
Intensity of perceived aroma quality during the consumption of the lemon-flavored model beverages. Each intensity is the mean value of 10 panelists using a seven-point scale from 1 to 7. Error bars show the standard deviations. The different letters indicate significant differences (Tukey's test, p < 0.05).
These results suggested that differences in aroma perceptions according to the types of sweeteners in the model beverages resulted from factors other than the sweetness level, sourness level and aroma content in the beverages, since, aside from the types of sweeteners and their concentrations, each model beverage consisted of the same ingredients and composition. As previously mentioned, it has been shown that the aroma release from beverages varied according to the types of sweeteners and their concentrations (Da Porto et al., 2006; Deibler and Acree, 2000; Hansson et al., 2001; King et al., 2006; Nahon et al., 1998; Rabe et al., 2003), and differences in aroma release could affect the aroma perceptions of the beverages (Deibler and Acree, 2000; King et al., 2006; Nahon et al., 1998). Therefore, it is possible that differences in aroma perceptions of the model beverages could be the result of changes in aroma release, due to the concentrations of the sweeteners or the physicochemical interactions between the ingredients in the beverage base and the odorants.
Influence of Sweeteners on the In Vivo Aroma Release during Consumption of the Model Beverages In order to investigate in detail the influence of the sweeteners on the in vivo aroma release, the amounts of odorants exhaled through the nostrils during the consumption of the model beverages were compared by the 4 trained panelists using R-FISS. As a result, the amounts of in-mouth odorants showed individual differences (Table 3). Previous studies have already indicated that the chemical structure of some odorants can be changed by the enzymatic activities of human saliva in the mouth (Buettner, 2002a; Buettner, 2002b). Based on these results, differences in the in vivo aroma release among panelists might result from differences in the oral cavity, volume and composition of the saliva, or swallowing activity. Thus, the in vivo aroma release showed individual differences, but there were no in-mouth odorants that showed significant differences in their amounts common to the 4 panelists (Table 3). Therefore, it was found that the types of sweeteners or their concentrations likely had only a small impact on the in vivo aroma release during the consumption of the model beverages, whereas their aroma perceptions significantly differed in the sensory evaluation.
| Compound | Panelist 1 | Panelist 2 | ||||||
|---|---|---|---|---|---|---|---|---|
| Amount (ng) | Amount (ng) | |||||||
| Sucrose | ACK | ASP | Sucralose | Sucrose | ACK | ASP | Sucralose | |
| α-pinene | 17 ± 3.9 | 22 ± 8.9 | 13 ± 4.1 | 24 ± 6.6 | 32 ± 7.1 | 21 ± 3.5 | 28 ± 10.1 | 23 ± 5.7 |
| camphene | 11 ± 2.2 | 13 ± 5.2 | 8 ± 2.6 | 15 ± 4.1 | 18 ± 4.4 | 12 ± 2.0 | 15 ± 6.2 | 13 ± 3.3 |
| myrcene | 23 ± 4.2 | 24 ± 10.9 | 24 ± 4.6 | 25 ± 5.7 | 33 ± 7.5 | 34 ± 8.1 | 31 ± 8.6 | 27 ± 7.5 |
| γ-terpinene | 189 ± 33.6 | 237 ± 69.5 | 192 ± 33.2 | 208 ± 47.6 | 286 ± 77.7 | 276 ± 62.4 | 251 ± 72.3 | 234 ± 69.9 |
| terpinolene | 46 ± 9.5 | 60 ± 17.7 | 46 ± 8.8 | 47 ± 9.9 | 73 ± 22.3 | 57 ± 20.4 | 64 ± 20.5 | 43 ± 15.1 |
| neral | 20 ± 1.5 | 18 ± 1.9 | 17 ± 2.6 | 18 ± 1.8 | 16 ± 2.3 a | 8 ± 1.9 b | 12 ± 2.0 ab | 10 ± 2.4 ab |
| geranial | 21 ± 1.9 | 17 ± 1.8 | 18 ± 1.7 | 19 ± 2.3 | 16 ± 2.0 a | 9 ± 1.6 b | 13 ± 2.4 ab | 10 ± 2.4 b |
| neryl acetate | 81 ± 00 | 79 ± 00 | 66 ± 19.1 | 79 ± 12.8 | 144 ± 64.9 | 67 ± 47.0 | 105 ± 31.2 | 110 ± 37.6 |
| geranyl acetate | 21 ± 1.2 | 19 ± 1.8 | 16 ± 4.0 | 19 ± 2.3 | 35 ± 14.8 | 16 ± 10.5 | 26 ± 7.6 | 25 ± 9.0 |
| nerol | 46 ± 12.4 | 35 ± 8.5 | 30 ± 13.3 | 34 ± 8.2 | 29 ± 6.7 | 8 ± 4.4 | 23 ± 3.6 | 23 ± 4.6 |
| geraniol | 37 ± 9.0 | 39 ± 9.9 | 25 ± 5.6 | 37 ± 4.3 | 41 ± 5.8 | 16 ± 5.6 | 34 ± 5.5 | 30 ± 3.8 |
| Compound | Panelist 3 | Panelist 4 | ||||||
|---|---|---|---|---|---|---|---|---|
| Amount (ng) | Amount (ng) | |||||||
| Sucrose | ACK | ASP | Sucralose | Sucrose | ACK | ASP | Sucralose | |
| α-pinene | 15 ± 3.6 ab | 12 ± 1.7 a | 20 ± 00 b | 18 ± 4.7 ab | 16 ± 3.3 | 15 ± 5.0 | 11 ± 4.6 | 13 ± 4.5 |
| camphene | 10 ± 2.3 ab | 7 ± 1.1 a | 12 ± 1.6 b | 11 ± 3.0 b | 9 ± 2.0 | 9 ± 2.7 | 7 ± 2.7 | 7 ± 2.8 |
| myrcene | 25 ± 3.0 a | 28 ± 3.6 ab | 37 ± 4.8 b | 32 ± 8.6 ab | 13 ± 3.9 | 12 ± 4.8 | 10 ± 4.1 | 10 ± 4.5 |
| γ-terpinene | 216 ± 34.1 | 241 ± 40.8 | 298 ± 51.3 | 251 ± 66.9 | 132 ± 27.8 | 120 ± 61.7 | 95 ± 38.1 | 97 ± 50.5 |
| terpinolene | 52 ± 7.8 | 66 ± 10.1 | 80 ± 18.6 | 60 ± 16.0 | 31 ± 5.9 | 28 ± 16.2 | 21 ± 9.7 | 21 ± 11.8 |
| neral | 21 ± 0.8 | 21 ± 5.0 | 16 ± 1.5 | 17 ± 1.5 | 7 ± 1.2 a | 5 ± 0.5 ab | 4 ± 0.9 b | 6 ± 1.4 ab |
| geranial | 21 ± 0.8 | 21 ± 4.1 | 18 ± 1.7 | 18 ± 1.6 | 7 ± 1.2 | 5 ± 0.3 | 5 ± 1.3 | 6 ± 1.1 |
| neryl acetate | 126 ± 24.1 | 149 ± 57.6 | 91 ± 37.0 | 108 ± 29.5 | 63 ± 20.5 a | 30 ± 7.7 b | 22 ± 10.1 b | 32 ± 13.0 b |
| geranyl acetate | 30 ± 5.2 | 35 ± 13.9 | 24 ± 7.5 | 30 ± 7.1 | 14 ± 4.3 a | 7 ± 2.5 b | 5 ± 2.0 b | 8 ± 2.9 ab |
| nerol | 38 ± 4.5 | 34 ± 9.0 | 27 ± 3.5 | 33 ± 5.4 | 23 ± 3.1 a | 13 ± 2.3 b | 11 ± 3.8 b | 19 ± 7.3 ab |
| geraniol | 35 ± 11.2 | 46 ± 10.9 | 30 ± 4.7 | 33 ± 4.2 | 24 ± 3.4 a | 9 ± 1.4 b | 10 ± 5.8 b | 13 ± 5.7 b |
Although previous studies reported that the aroma release from beverages varied by the types of sweeteners and their concentrations (Da Porto et al., 2006; Deibler and Acree, 2000; Hansson et al., 2001; King et al., 2006; Nahon et al., 1998; Rabe et al., 2003), it is also possible that these changes are not noticeable within the range of the sweetener concentration generally used for beverages (Nahon et al., 1998; Rabe et al., 2003). Therefore, sweeteners might have a small impact on the in vivo aroma release due to the low concentrations of the sweeteners in the model beverages used in this study.
It was also reported that each sweetener has a different taste profile (Hanger et al., 1996; Wiet and Beyts, 1992). ACK has a sweet taste, accompanied by a relatively stronger bitter taste than other sweeteners (Hanger et al., 1996; Wiet and Beyts, 1992). ASP and sucralose have a relatively stronger sweet aftertaste than sucrose (Hanger et al., 1996) in addition to the sweet taste quality that is similar to sucrose. Therefore, the bitter taste might have an inhibitory effect on the perceived lemon-like aroma, and the sweet aftertaste might have an enhancing effect on the perceived green/spicy aroma. Previous studies have already indicated the possibility that the multi-modal interactions between multiple stimuli elicited by the aroma and taste compounds (taste-aroma interactions) in foods could change their perceived aroma intensities (Baldwin et al., 2008; Green et al., 2012; Hewson et al., 2009). Considering the present results, it is highly likely that the taste-aroma interactions caused by the aroma and taste compounds would have a significant impact on differences in the aroma perceptions of the beverages containing different sweeteners.
The present results suggested that differences in aroma perceptions according to the types of sweeteners in the model beverages would result from factors other than the amounts of in-mouth odorants exhaled from the human nose. Furthermore, it was inferred that the taste-aroma interactions could be one of the factors having a significant impact on the different aroma perceptions of the beverages containing different sweeteners. Sweeteners could, however, have an influence on the release kinetics of the in-mouth odorants during the consumption of the beverages, and consequently, change the composition of the retronasal aroma. Changes in the aroma composition due to the sweeteners may result in different aroma perceptions of the beverages. A future important challenge will be to understand the relationship between the taste compounds including sweeteners, in vivo aroma release, and their aroma perceptions resulting from multiple stimuli elicited by the aroma and taste compounds.
