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Modulation of sensory perception of cheese attributes intensity and texture liking via ortho- and retro-nasal odors
Accepted Manuscript Modulation of sensory perception of cheese attributes intensity and texture liking via ortho- and retro-nasal odors P. Han, T. Fark, R. de Wijk, N. Roudnitzky, E. Iannilli, H-S. Seo, T. Hummel PII: DOI: Reference:
S0950-3293(18)30761-4 https://doi.org/10.1016/j.foodqual.2018.11.019 FQAP 3612
To appear in:
Food Quality and Preference
Received Date: Revised Date: Accepted Date:
13 September 2018 29 October 2018 21 November 2018
Please cite this article as: Han, P., Fark, T., de Wijk, R., Roudnitzky, N., Iannilli, E., Seo, H-S., Hummel, T., Modulation of sensory perception of cheese attributes intensity and texture liking via ortho- and retro-nasal odors, Food Quality and Preference (2018), doi: https://doi.org/10.1016/j.foodqual.2018.11.019
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Modulation of sensory perception of cheese attributes intensity and texture liking via orthoand retro-nasal odors Han P1*, Fark T1, de Wijk R2,3, Roudnitzky N1, Iannilli E1, Seo H-S4, and Hummel T1 1
Smell & Taste Clinic, Department of Otorhinolaryngology, Technical University of Dresden
Medical School, Fetscherstrasse 74, 01307 Dresden, Germany; 2Top Institute Food and Nutrition,
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Wageningen Food & Biobased Research, Consumer Science & Health,
Wageningen, The Netherlands, 4Department of Food Science, University of Arkansas, 2650 North Young Avenue, Fayetteville, AR 72704, USA Full names and titles of authors: Dr. Pengfei Han (PhD), Therese Fark (MD), Dr. Rene A. de Wijk (PhD), Dr. Emilia Iannilli (PhD), Dr. Han-Seok Seo (PhD), Professor Dr. med. Thomas Hummel (MD) Correspondence to: Pengfei Han, PhD., [email protected]. Smell & Taste Clinic, Department of Otorhinolaryngology, Technical University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany; phone +49-351-458-4189; fax: +49-351-4587130. Conflicts of interests: The authors declare no conflict of interest. Acknowledgements: We would like to thank C Ponne, C Kersch, and B Schuster for their help with the study.
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Abstract Cross-modal sensory integration plays a key role in food flavor perception and acceptance during consumption. The current study investigated the effect of a butter odor, delivered at various stages of oral processing cycle, on modulating the sensory properties of cheese. Twenty healthy volunteers (aged between 25 and 29 years, 12 women) were measured for their detection thresholds for the butter odor. In the sensory evaluation sessions, participants chewed and swallowed three types of cheese (low-fat, 20% fat content, LF; a medium-fat, 30% fat content, MF; high-fat, 40% fat content, HF, served in 16×16×12 mm3 cubes) while the butter odor was presented ortho- and retronasally in two concentrations at various points of the oral processing cycle. After swallowing, participants rated on a visual analogue scale for the intensities of cheese creaminess, butter note, overall flavor, and the pleasantness for cheese texture. Enhancement of added butter odor on perceived sensory attributes differed as a function of the delivery routes and timings. Creaminess intensity increased significantly when butter odor presented retro-nasally at the start of chewing. Butter note was enhanced when the retro-nasal odor was added during chewing. The texture pleasantness was increased with ortho-nasal odor presentation. In addition, for the creaminess intensity and texture liking enhancement, the observed effects were more pronounced with butter odor presentation at the lower concentration. Taken together, these findings suggested the importance of temporal congruency for cross-modal sensory enhancement in food flavor perception. The findings help to better understand flavor perception during oral processing of solid food, and add value for future development of foods with nutritional benefits. Key words: Cross-modal sensory enhancement; orthonasal; retronasal; cheese; texture; congruency
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Introduction Flavor is one of the most important attributes for food evaluation. Food flavor perception involves multisensory interaction in which signals from different sensory channels, including olfactory, gustatory, mechanical, trigeminal and even auditory sources merge and form a whole sensory percept (Seo and Hummel 2017). Sensory signals from different modalities often interact (enhancement or suppression) with each other and modulate the whole flavor perception. Odors not only contribute to the qualitative diversity of food, but also interact with other sensations and modulate the overall flavor perception. The most studied crossmodal sensory enhancement is between odor and taste, which often form the unitary flavor of food (Dalton et al. 2000), with a number of previous studies having shown odor enhancement by taste (Green et al. 2012; Welge-Lussen et al. 2009) or taste enhancement by odors (Labbe et al. 2006; Labbe et al. 2007; Sakai et al. 2001; Schifferstein and Verlegh 1996). The cross-modal sensory enhancement largely depends on the quality and temporal congruency of individual sensory stimuli. The quality congruency refers to the extent to which signals for distinct modalities could be considered attributes to the same object. For example, the salty- or sweet- congruent odor could enhance the saltiness and sweetness perception, respectively (Seo et al. 2013; Small et al. 2004). In the opposite direction, Green (2012) showed that sucrose, but not other tastants (NaCl, citric acid), significantly enhanced the perceived intensity of citral, vanillin, and furaneol - an strawberry odor. Quality congruency also influences the pleasantness, intensity and familiarity of the flavor perception. A recent study showed the odor-taste pairs were rated as more pleasant with increasing levels of congruency (Amsellem and Ohla 2016). In addition, the presence of a congruent taste significantly increased the localization of retronasal food odors to the tongue, known as the oral referral of retronasal odor perception (Fondberg et al. 2018; Lim et al. 2014; Lim and Johnson 2011; 2012). Neuroimaging studies also suggested a neural mechanism for the super additive effect of multisensory integration, in which certain brain areas (including insula, orbitofrontal cortex, amygdala and anterior cingulate cortex) respond to stimuli of different modalities (e.g. odor, taste or texture) and exhibit a larger response to their combinations than the sum of responses to each individual stimulus (de Araujo et al. 2003; Onuma et al. 2018; Small et al. 2004; Verhagen and Engelen 2006). The enhancement of perceptual as well as neural responses depends on familiarity and prior experiences with the stimulus (Frank and Byram 1988; Small et al. 2004). In addition, the quality congruency depends on the route of odor delivery, especially for foods. For instance, a number of studies reported the 3
enhancement of taste intensity by odor delivered via the retronasal route (Lawrence et al. 2009; Manabe et al. 2014; Stevenson et al. 1999). This is due to the fact that retronasal odors are more referred to the mouth to elicit flavor that represents known or potential foods (Lim and Johnson 2012). Apart from quality congruency, the congruency in the temporal dimension (e.g. timing of the delivery of sensory stimuli from different sensory modalities) is also important for multisensory enhancement (Isogai and Wise 2016). Holding a subthreshold concentration of saccharine in the mouth decreased detection thresholds for a sweet almond aroma, but odor thresholds were not affected when subjects expectorated the saccharine solution before sampling the odor (Pfeiffer et al. 2005). Recently, Kakutani and colleagues (Kakutani et al. 2017) compared the sweet taste intensity when a vanilla odor was presented synchronously with breathing via either orthonasal or retronasal route either before or after drinking the solution. Taste enhancement was observed only when the odor was presented retronasally and subjects exhaled after drinking the beverage, suggesting the importance of both the route of odor delivery and the temporal synchrony between odor and taste for the enhancement (Kakutani et al. 2017). Similar findings have been found for texture enhancement by odor. Retronasal aroma increased rated creaminess of dairy samples most when odor was presented during swallowing, less when presented while subjects manipulated the dairy sample in the mouth before swallowing, and not at all when the odor was presented while the mouth was filling (Bult et al. 2007). In another study, the enhancement of sweetness and bitterness by “sweet” and “bitter” odors was greatest with simultaneous presentation, and the enhancement was largely attenuated when the odor was presented before or after the delivery of taste with only one second of deviation (Isogai and Wise 2016). Food odor does not only have an impact on taste perception, but also on food texture. Previous research suggested that specific texture sensations such as creaminess, a highly desirable food property, are multi-modal percepts reflecting odor, taste, textural and, possibly, hedonic properties of foods (de Wijk et al. 2006). The interaction between odor and texture has been shown in previous studies (Hollowood et al. 2002; Pangborn et al. 1978). Food texture (e.g. creaminess or thickness) is also important for overall food sensory characteristics, especially for certain types of food such as milk products. It has been found that increased viscosity of beverages reduces retronasal odor intensity (Pangborn et al. 1978). Our previous work showed higher ratings for milk thickness and creaminess when butter-like odor was presented retronasally at the time of swallowing (Bult et al. 2007; Roudnitzky et al. 2011). 4
This pointed towards the temporal congruency of odor-texture enhancement in the late phase of oral processing. The first aim of the current study was to investigate the modulation of added odor on texture and flavor perceptions of a solid food - cheese. In addition, unlike previous research, the current study allowed subjects to chew the cheese ad libitum, trying to imitate eating situations in real life. A butter-like odor was presented at various stages of the eating cycle at the start of chewing, during chewing, and before swallowing, either through the orthonasal or retronasal route; multiple sensory attributes were rated. This study also tried to address the potential interaction between odor-texture enhancement with odor concentration and cheese type (e.g. fat level). We therefore included two concentrations of odor based on individual perceptual threshold and three types of cheese with varied fat content (high-fat, medium-fat and low-fat cheese). Materials and Methods Participants Twenty young healthy participants (12 females and 8 males) aged between 25 and 29 years took part in this study. Inclusion criteria were a normal sense of smell, as ascertained using the “Sniffin’ Sticks” test (Hummel et al. 1997), and self-reported regular consumption of Gouda cheese. The study was carried out in the Smell & Taste Clinic at the Department of Otorhinolaryngology of the TU Dresden, and the protocol was approved by the local Medical Ethical Committee (EK284122006). All participants were informed about the experimental procedure and provided informed written consent before participation. Odor stimuli The butter odor (Butter Buds Food Ingredients, Racine, WI, USA), a natural cream flavor, was used as odor stimulus. Two odor concentrations were selected for the study based on the individual threshold levels of the participants: the low concentration (LC) was just detectable for all subjects (5% above threshold - see below), whereas the high concentration (HC) was clearly detectable for all participants (twice the concentration of LC). Cheese stimuli The used cheeses were varieties of Gouda cheese ages less than two months. Gouda is the most popular type of Dutch cheese and accounts for approximately 50% of all Dutch cheeses. 5
Three Gouda cheese products (Friesland Foods, Meppel, The Netherlands) varying in fat level, i.e., low-fat (LF, 20% fat), medium-fat (MF, 30% fat), and high-fat (HF, 40% fat) cheeses, were used in this study. Using a cheese slicer (Genius, Limburg, Germany), each cheese sample was broken into bite-size cubes (16×16×12 mm). Procedure Participants took part in three sessions. In the first session, detection thresholds for butter odor were tested in an orthonasal way, using the method of ascending limits. Odorous stimuli of 1000 ms duration were presented to either left or right nostril (randomized selection) using a computer-controlled olfactometer (Burghart OM6b; Burghart, Wedel, Germany). Using the method of ascending limits the butter odor was delivered in ascending concentrations starting from the lowest concentration (5% v/v), and increased in steps of 5%. Participants were asked to answer “yes” or “no” whether an odor had been perceived or not. When participants perceived the odor at a certain concentration, they received the same concentration a second time. A threshold level was defined as the concentration where a given stimulus had been perceived twice in a row. The second and third sessions lasted approximately two hours each, during which all cheese stimuli were presented once in all experimental conditions. Participants were asked to chew each cheese cube ad libitum in the presence of either ortho- or retro-nasal odor at the low or high concentration level. The odor presentation followed the same procedure described previously (Bult et al. 2007). In the orthonasal condition (O), the odor stimulus was presented immediately after the cheese had been put into the mouth but before the onset of chewing (to mimic the natural situation where cheese is smelled ortho-nasally when the cheese is brought to the mouth). In the three retronasal conditions, the odor stimulus was presented retronasally at three different moments: at the start of chewing (R1), between the start and swallowing (R2), and during swallowing (R3). Oral chewing activity was measured using vibromyography (VMG) activity of the prelaryngeal, submandibular, buccal, and temporal muscles (de Wijk et al. 2008). VMG measurements allowed direct identification of the onsets of chewing and swallowing which served as triggers for odor delivery. The inter-stimulus interval between cheese stimuli was approximately 4 min to minimize adaptation. In addition to eight odor conditions (i.e., four instants of odor presentation × two odor concentrations), a control condition (C) was included without any odor presentation which was also applied with any of the three cheese stimuli. Therefore, the total number of stimulus conditions was 27 6
(i.e., 9 odor conditions × 3 cheese types) and each stimulus condition was tested in duplicate through the second and third sessions. Participants were asked to evaluate the intensities for cheese creaminess, butter note, overall flavor, and the pleasantness for cheese texture. Ratings for cheese sensory attributes were performed using the visual analogue scales (VAS): for intensity ratings the VAS ranged from 0 (not creamy / no butter note / no flavor) to 100 (very creamy / very strong butter note / very strong flavor), and for the texture pleasantness rating the VAS ranged from 0 (unpleasant) to 100 (pleasant) with a central marker indicating neutral.
Figure 1 Diagram showing the experimental procedure for one type of cheese under one odor stimulus concentration. Cells in grey indicate the timepoints for different conditions for odor stimuli and ratings for sensory attributes. Odor stimulus was presented orthonasally for 3 s after food intake and before chewing (O1). Odor stimulus was presented retronasally for 3 s at the three different instants: at the start of chewing (R1), half-way between chewing and swallowing (R2), or during swallowing (R3). Statistical analysis Data analysis was conducted using SPSS for WindowsTM (version 24.0, IBM SPSS Inc., Chicago, IL, USA), GraphPad Prism (Version 6, GraphPad Software, Inc. La Jolla, CA), and XLSTAT statistical software (Addinsoft, New York, NY, USA). To determine whether odor condition (i.e., O, R1, R2, R3, and C) could affect attribute intensities and texture likings of three types of cheese (i.e., LF, MF, and HF), a three-way analysis of variance (ANOVA), treating “odor condition” and “cheese type” as fixed effects and “participants” as a random effect, was performed as a function of odor concentration (i.e., L and H). Post-hoc comparisons between independent variables were performed using Tukey’s Honest Significant Difference (HSD) method. A statistically significant difference was defined as p < 7
0.05. To examine associations between odor condition (i.e., O, R1, R2, R3, and C) and attribute intensities and likings of cheese stimuli, principal component analysis (PCA) on covariance matrix was conducted using XLSTAT statistical software. Results Butter odor threshold The individual thresholds for butter odor are shown in Table 1. The averaged butter odor threshold was 14.75 (1.87), with 95% confidence interval (CI) 10.84 (lower CI) and 18.66 (higher CI) at 500-ms stimulation. The mean threshold was 9.25 (SEM 1.63), with the 95% CI 5.83 (lower CI) and 12.67 (upper CI) at 1000-ms stimulation. There was a significant effect of gender on threshold, showing that female participants were more sensitive to butter odor than male participants (F = 5.68, p = 0.03). There was no effect of nostril sides (F = 0.18, p = 0.68) or interaction between gender and nostril side (F = 0.18, p = 0.68) on butter odor threshold. Participants’ information and threshold levels are shown in the supplementary Table 1. Creaminess Low concentration level of butter odor There was no significant interaction between odor condition and cheese type in the ratings of creaminess intensity (F = 2.74, p = 0.22). The odor condition had a significant impact on creaminess perception (F = 2.74, p = 0.035). Post-hoc test showed that the creaminess intensity ratings in the R1 odor condition were greater than those in the R3 odor condition (p = 0.01). Creaminess intensities significantly differed with a fat level of cheese stimuli (F = 45.51, p < 0.001), with highest creaminess rating for HF, followed by MF and the LF cheese stimuli. High concentration level of butter odor There was no significant interaction between odor condition and cheese type in the ratings of creaminess intensity (F = 0.89, p = 0.53). Creaminess intensities were not significantly different as a function of odor condition (F = 0.14, p = 0.97), but differed in relation to the fat level of cheese stimuli (F = 51.32, p < 0.001), with highest creaminess ratings for HF, followed by MF and the LF cheese stimuli. 8
Figure 2: Mean ratings of creaminess intensity for cheese stimuli in the absence (control) or the presence of butter odor. Odor stimulus at either a low or a high concentration was presented via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. Butter note Low concentration level of butter odor There was no significant interaction between odor condition and cheese type in the intensity ratings of the butter note (F = 1.15, p = 0.34). Butter note intensities significantly differed by odor condition (F = 6.50, p < 0.001), with the butter note intensity being significantly higher in all odor conditions as compared to control conditions (i.e., no odor), as shown in Figure 2. In addition, perceived butter note intensity was highest when the odor was delivered during chewing (R2). Intensities of butter note during chewing (R2) was greater than those before chewing (i.e., orthonasal condition, “O”) and in the control condition (Figure 2). Intensity ratings of butter note were significantly greater in relation to the fat level of cheese stimuli (F = 11.29, p < 0.001), with highest butter note ratings for HF, followed by MF and the LF cheese stimuli. High concentration level of butter odor 9
There was no significant interaction between odor condition and cheese type in the intensity ratings of butter note (F = 0.63, p = 0.75). Butter note intensities were significantly different by odor condition (F = 6.24, p < 0.001). Similar to the trend at the lower concentration level of butter note, butter note intensities in the control condition (i.e., no odor) were significantly lower than other conditions with butter odor presentation, and butter note intensities in the R2 condition were greater than those in the O and control conditions (Figure 2). Intensity ratings of butter note significantly increased with the fat level of cheese stimuli (F = 7.09, p = 0.002), with highest butter note ratings for HF, followed by MF and the LF cheese stimuli.
Figure 3: Mean ratings of butter notes intensity for cheese stimuli in the absence (control) or the presence of butter odor. Odor stimulus at either a low or a high concentration was presented via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. Pleasantness of cheese texture Low concentration level of butter odor There was no significant interaction between odor condition and cheese type in the pleasantness ratings of cheese texture (F = 0.68, p = 0.71). Pleasantness ratings of cheese texture were significantly different as a function of odor condition (F = 2.86, p = 0.03), with higher ratings of texture pleasantness in the O condition than in the R3 condition; there were 10
no other pairwise differences between odor conditions. Pleasantness ratings of cheese texture significantly increased with a fat level of cheese stimuli (F = 11.10, p < 0.001), with highest texture liking for FF, followed by MF and the LF cheese stimuli. High concentration level of butter odor There was no significant interaction between odor condition and cheese type in the pleasantness ratings of cheese texture (F = 0.84, p = 0.57). Pleasantness ratings of cheese texture were not significantly different by odor condition (F = 0.27, p = 0.90). Pleasantness ratings of cheese texture significantly increased with a fat level of cheese stimuli (F = 10.26, p < 0.001), with highest texture liking for FF, followed by MF and the LF cheese stimuli.
Figure 4: Mean ratings of texture pleasantness for cheese stimuli in the absence (control) or the presence of butter odor. Odor stimulus at either a low or a high concentration was presented via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. Overall flavor Low concentration level of butter odor
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A significant interaction between odor condition and cheese type was observed in the intensity ratings of overall flavor of cheese stimuli (F = 2.48, p = 0.02). More specifically, a significant effect of odor condition on overall flavor intensity was present with MF cheese (F = 3.12, p = 0.02); the ratings for overall flavor intensity were significantly higher at O condition as compared to R1 (p = 0.03), but not with LF (F = 2.13, p = 0.09) or HF (F = 0.53, p = 0.72) cheese stimuli. There was no significant effect of odor condition (F = 0.29, p = 0.89) or cheese type (F = 2.60, p = 0.09) on intensity ratings of overall flavor.
Figure 5: Mean ratings of overal flavour intensity for cheese stimuli varied in their fat content (MF, medium-fat; HF, high-fat; LF, low-fat) in the absence (control) or the presence of butter odor presented at a low concentration via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. High concentration level of butter odor There was no significant interaction between odor condition and cheese type in the intensity ratings of overall flavor of cheese stimuli (F = 0.94, p = 0.48). Intensity ratings of overall flavor did not differ in relation to the odor condition (F = 1.27, p = 0.29) or the cheese type (F = 2.63, p = 0.09). Associations of odor condition with attribute intensity and liking
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Biplot representations of the principal component analysis (PCA) performed for the low and high odor concentration levels are shown in Figure 3. The first principal component (PC1) accounting for 64.09% and 79.22% of the total variance is related to the temporal congruency (timing of odor presentation), and separated butter note from other sensory attributes. The second component (PC2) accounted for 26.20% and 20.05% of the total variance and suggested an overall enhancement of the cheese sensory attributes by added odor. The PC1 in both low and high odor concentration conditions mainly represents information linked to butter note intensity. At both odor concentration levels, there was a positive association between butter note intensity and added odor via retronasal route especially at R2 (Figure 3A and 3B). When cheese was consumed in the presence of butter odor at a low concentration level, the creaminess intensities were more associated with retronasal odors presented at the onset of chewing (R1) (Figure 3A), however, the added odor (R1) at the high concentration had little impact on the creaminess intensity (Figure 3B). Additionally we saw more differentiation between attributes and conditions in the low compared to the high odor concentration.
Figure 6: Bi-plots of principal component analysis (PCA) showing the associations of four odor conditions with creaminess, butter note, and overall flavor intensities and texture pleasantness of cheese stimuli as a function of odor concentration level: low (A) and high (B) concentration levels of butter odor. Discussion
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The present study confirmed the effects of an added butter odor on perceived creaminess, butter note, total flavor and the texture pleasantness for cheese with different levels of fat contents. The odor presentations varied in pathways (either ortho- or retro-nasal) and timings (at start of chewing, during chewing or during swallowing). The results demonstrated enhancement of creaminess ratings and butter note intensity, as well as texture liking by the added odor which varied with timing of presentation, and cheese type (fat content). In addition, the observed effects were more pronounced when the odor was added at a lower odor concentration. The enhancement of perceived cheese attributes by added butter odor is in line with the temporal congruency for cross-modal sensory perceptions. First, creaminess ratings increased when the butter odor was presented retro-nasally at the start of chewing (R1). This finding is in line with the temporal congruency theory for cross-modal sensory integration, in which the enhancement of cheese sensory attributes by retronasal odors depends on a temporal binding window (Isogai and Wise 2016). This is the point when the cheese interacts with oral surface and saliva, and the initiation of the physical breakdown (de Wijk et al. 2006). Similar findings were observed for liquid dairy products (i.e. milk) (Bult et al. 2007). Other studies found higher ratings of fatty intensity without nose clips compared with nose clips on, indicating the role for retronasal odor perception on texture perception (Zhou et al. 2016). In addition, human neuroimaging study showed retronasal odor stimulation was related to brain activation at the base of the central sulcus, corresponding to the primary representation of the oral cavity, possibly reflecting that retronasal odors are referred to the mouth (Small et al. 2005). Another study reported the enhanced activation of the mechanosensory area in response to sweetened milk when a butter note odor was presented via retronasal route (Iannilli et al. 2014). Moreover, the textural and olfactory inputs converge in the insular cortex which serves as the neural mechanism for the cross-modal sensory enhancement (Rolls 2012; Small 2012). The butter note intensity peaked when the odor was presented retronasally while the cheese was being chewed but before swallowing (R2 condition). This timing is mainly followed by an exhalation where the volatile compounds travel to the olfactory receptor via the retronasal route (Roudnitzky et al. 2011). Butter note is mainly contributed by diacetyl which is released from the cheese during chewing (Curioni and Bosset 2002). This finding suggests that the butter note is perceived while the cheese is under oral processing and the key volatile and non-volatile compounds are released from the cheese-saliva bolus (Feron et al. 2014). As for the texture pleasantness, an increased rating was observed when butter odor was presented 14
orthonasally at the lower concentration. This mimics the situation in which the cheese odor reaches the consumers’ nose before chewing the cheese. This suggests an influence of odor on the expectation of texture pleasantness. Again, this finding is in line with previous findings showing that odors can affect texture attributes and vice versa (Bult et al. 2007). However, the enhancement of perceived cheese creaminess and overall flavor intensity was more pronounced when the butter odor was presented at the lower concentration. This might be due to the higher odor concentration being perceived as less pleasantness (Sano et al. 2002). Results from the current study suggested the enhancement of perceived cheese sensory attributes were dependent on the added odor concentration, with higher effectiveness at lower compared to higher butter odor concentrations. This was also reflected in a more differential pattern between attributes and conditions in the low compared to the high odor concentration in PCA result. It was possible that the higher odor concentration, twice as high as the detective threshold, evoked irritation, which may in turn diminish the effect of odor-taste enhancement. Besides, higher odor concentration may be also related to changed quality (Gross-Isseroff and Lancet 1988) or valence perceptions (Rouby et al. 2009). Previous studies have reported the taste enhancement by odor at relatively lower rather than higher concentration levels (Labbe et al. 2007; Seo et al. 2013). Findings from the current study may have implications for developing novel foods with nutritional benefits. For example, it has been shown that the oro-sensory cues (such as creaminess) increased the satiating effect of a protein-rich beverage (Bertenshaw et al. 2013). Thicker products were able to generate expectations that they are more filling compared to their thinner counterparts (Hogenkamp et al. 2011; McCrickerd et al. 2012). Moreover, stronger sensory attributes could also contribute to satiety through a top-down modulation of hormone release (Yeomans et al. 2016), which may reduce excessive consumption of high fat foods. Therefore, the odor-enhanced texture perception may help to formulate foods with With increased satiating properties, but without adding calories (de Graaf 2012). This provides insights to formulating food products with low calories density, while preserving pleasantness and having higher satiating properties (Campbell et al. 2017; Saint-Eve et al. 2009). However, results from the current study also indicate that odor enhancing is highly specific and depends on factors such as the fat content of the food, the type and concentration of the odor. The current study has some limitations. First, the study was performed in young participants with a narrow age range, in order to minimize potential effects of age on olfactory function, 15
and, hence, on sensory evaluation. However, the results may not be representative of the general population. The participants were not trained so that individual differences regarding the interpretation of certain sensory attributes may confound the results. For example, while flavor is commonly known as the integration of taste, aroma, and trigeminal sensations, it is often confused with orthonasal olfactory perception; evaluation of selected sensory attributes in the current study emerged from integrated sensations of visual, olfactory, gustatory, and tactile cues (Chen and Eaton 2012). A group of experienced panellists would make the findings more reliable. Second, since the study used a single odorant with butter note, it is possible that the effect of butter odor is potent and specific for certain sensory attributes; it may be weak for others, given the complexity of cheese flavor. Future study could use other key odors derived from cheese that contribute to certain sensory characteristics. Third, although we controlled the timing of odor delivery, the oral processing was ad libitum which may result in different levels of flavor release between conditions. Besides, 5% of butter odor was assigned for the threshold level for most of the participants, which also the lowest concentration level used for the threshold testing. Therefore, it was possible that the actual threshold level was below than 5%, which may result in different outcomes. Lastly, tiredness due to long testing duration and satiety effect with cheese consumption over time may have impacted on the results shown here. In conclusion, the current study adds to the increasing knowledge that sensory perception can be modified substantially by adding an odor which is an expression of the intimate connection between all the sensory channels involved in flavor perception.
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Labbe D, Damevin L, Vaccher C, Morgenegg C, Martin N. 2006. Modulation of perceived taste by olfaction in familiar and unfamiliar beverages. Food Qual Prefer 17: 582-589. Labbe D, Rytz A, Morgenegg C, Ali S, Martin N. 2007. Subthreshold olfactory stimulation can enhance sweetness. Chem Senses 32: 205-214. Lawrence G, Salles C, Septier C, Busch J, Thomas-Danguin T. 2009. Odour–taste interactions: A way to enhance saltiness in low-salt content solutions. Food Quality and Preference 20: 241-248. Lim J, Fujimaru T, Linscott TD. 2014. The role of congruency in taste–odor interactions. Food Quality and Preference 34: 5-13. Lim J, Johnson MB. 2011. Potential mechanisms of retronasal odor referral to the mouth. Chem Senses 36: 283-289. Lim J, Johnson MB. 2012. The role of congruency in retronasal odor referral to the mouth. Chem Senses 37: 515-522. Manabe M, Ishizaki S, Yamagishi U, Yoshioka T, Oginome N. 2014. Retronasal Odor of Dried Bonito Stock Induces Umami Taste and Improves the Palatability of Saltiness. J Food Sci. McCrickerd K, Chambers L, Brunstrom JM, Yeomans MR. 2012. Subtle changes in the flavour and texture of a drink enhance expectations of satiety. Flavor 1: 20. Onuma T, Maruyama H, Sakai N. 2018. Enhancement of Saltiness Perception by Monosodium Glutamate Taste and Soy Sauce Odor: A Near-Infrared Spectroscopy Study. Chem Senses 43: 151-167. Pangborn RM, Gibbs ZM, Tassan C. 1978. Effect of hydocolloids on apparent viscosity and sensory properties of selected beverages. Journal of Texture Studies 9: 415-436. Pfeiffer JC, Hollowood TA, Hort J, Taylor AJ. 2005. Temporal synchrony and integration of subthreshold taste and smell signals. Chem Senses 30: 539-545. Rolls ET. 2012. Taste, olfactory and food texture reward processing in the brain and the control of appetite. Proc Nutr Soc 71: 488-501. Rouby C, Pouliot S, Bensafi M. 2009. Odor hedonics and their modulators. Food Quality and Preference 20: 545-549. Roudnitzky N, Bult JH, de Wijk RA, Reden J, Schuster B, Hummel T. 2011. Investigation of interactions between texture and ortho- and retronasal olfactory stimuli using psychophysical and electrophysiological approaches. Behav Brain Res 216: 109-115. Saint-Eve A, Lauverjat C, Magnan C, Déléris I, Souchon I. 2009. Reducing salt and fat content: Impact of composition, texture and cognitive interactions on the perception of flavoured model cheeses. Food Chemistry 116: 167-175. Sakai N, Kobayakawa T, Gotow N, Saito S, Imada S. 2001. Enhancement of sweetness ratings of aspartame by a vanilla odor presented either by orthonasal or retronasal routes. Percept Mot Skills 92: 1002-1008. Sano K, Tsuda Y, Sugano H, Aou S, Hatanaka A. 2002. Concentration effects of green odor on eventrelated potential (P300) and pleasantness. Chem Senses 27: 225-230. Schifferstein HN, Verlegh PW. 1996. The role of congruency and pleasantness in odor-induced taste enhancement. Acta Psychol (Amst) 94: 87-105. Seo HS, Hummel T. 2017. Cross-Modal Integration in Olfactory Perception. In: Buettner A, editor, Handbook of Odor. Switzerland: Springer, Cham. p. 115-116. Seo HS, Iannilli E, Hummel C, Okazaki Y, Buschhuter D, Gerber J, Krammer GE, van Lengerich B, Hummel T. 2013. A salty-congruent odor enhances saltiness: functional magnetic resonance imaging study. Hum Brain Mapp 34: 62-76. Small DM. 2012. Flavor is in the brain. Physiol Behav 107: 540-552. Small DM, Gerber JC, Mak YE, Hummel T. 2005. Differential neural responses evoked by orthonasal versus retronasal odorant perception in humans. Neuron 47: 593-605. Small DM, Voss J, Mak YE, Simmons KB, Parrish T, Gitelman D. 2004. Experience-dependent neural integration of taste and smell in the human brain. J Neurophysiol 92: 1892-1903. Stevenson RJ, Prescott J, Boakes RA. 1999. Confusing Tastes and Smells: How Odours can Influence the Perception of Sweet and Sour Tastes. Chem Senses 24: 627-635. 18
Verhagen JV, Engelen L. 2006. The neurocognitive bases of human multimodal food perception: sensory integration. Neurosci Biobehav Rev 30: 613-650. Welge-Lussen A, Husner A, Wolfensberger M, Hummel T. 2009. Influence of simultaneous gustatory stimuli on orthonasal and retronasal olfaction. Neurosci Lett 454: 124-128. Yeomans MR, Re R, Wickham M, Lundholm H, Chambers L. 2016. Beyond expectations: the physiological basis of sensory enhancement of satiety. Int J Obes (Lond) 40: 1693-1698. Zhou X, Shen Y, Parker JK, Kennedy OB, Methven L. 2016. Relative Effects of Sensory Modalities and Importance of Fatty Acid Sensitivity on Fat Perception in a Real Food Model. Chemosens Percept 9: 105-119.
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Influences of odor concentration, delivery route and timing on cheese sensory attributes were studied.
Retronasal odor added during chewing enhanced perceived intensity of cheese creaminess and butter note.
Observed effects were more pronounced with butter odor presentation at the lower concentration.
Qualitative and temporal congruencies are important for cross-modal sensory enhancement.
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S0950-3293(18)30761-4 https://doi.org/10.1016/j.foodqual.2018.11.019 FQAP 3612
To appear in:
Food Quality and Preference
Received Date: Revised Date: Accepted Date:
13 September 2018 29 October 2018 21 November 2018
Please cite this article as: Han, P., Fark, T., de Wijk, R., Roudnitzky, N., Iannilli, E., Seo, H-S., Hummel, T., Modulation of sensory perception of cheese attributes intensity and texture liking via ortho- and retro-nasal odors, Food Quality and Preference (2018), doi: https://doi.org/10.1016/j.foodqual.2018.11.019
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Modulation of sensory perception of cheese attributes intensity and texture liking via orthoand retro-nasal odors Han P1*, Fark T1, de Wijk R2,3, Roudnitzky N1, Iannilli E1, Seo H-S4, and Hummel T1 1
Smell & Taste Clinic, Department of Otorhinolaryngology, Technical University of Dresden
Medical School, Fetscherstrasse 74, 01307 Dresden, Germany; 2Top Institute Food and Nutrition,
3
Wageningen Food & Biobased Research, Consumer Science & Health,
Wageningen, The Netherlands, 4Department of Food Science, University of Arkansas, 2650 North Young Avenue, Fayetteville, AR 72704, USA Full names and titles of authors: Dr. Pengfei Han (PhD), Therese Fark (MD), Dr. Rene A. de Wijk (PhD), Dr. Emilia Iannilli (PhD), Dr. Han-Seok Seo (PhD), Professor Dr. med. Thomas Hummel (MD) Correspondence to: Pengfei Han, PhD., [email protected]. Smell & Taste Clinic, Department of Otorhinolaryngology, Technical University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany; phone +49-351-458-4189; fax: +49-351-4587130. Conflicts of interests: The authors declare no conflict of interest. Acknowledgements: We would like to thank C Ponne, C Kersch, and B Schuster for their help with the study.
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Abstract Cross-modal sensory integration plays a key role in food flavor perception and acceptance during consumption. The current study investigated the effect of a butter odor, delivered at various stages of oral processing cycle, on modulating the sensory properties of cheese. Twenty healthy volunteers (aged between 25 and 29 years, 12 women) were measured for their detection thresholds for the butter odor. In the sensory evaluation sessions, participants chewed and swallowed three types of cheese (low-fat, 20% fat content, LF; a medium-fat, 30% fat content, MF; high-fat, 40% fat content, HF, served in 16×16×12 mm3 cubes) while the butter odor was presented ortho- and retronasally in two concentrations at various points of the oral processing cycle. After swallowing, participants rated on a visual analogue scale for the intensities of cheese creaminess, butter note, overall flavor, and the pleasantness for cheese texture. Enhancement of added butter odor on perceived sensory attributes differed as a function of the delivery routes and timings. Creaminess intensity increased significantly when butter odor presented retro-nasally at the start of chewing. Butter note was enhanced when the retro-nasal odor was added during chewing. The texture pleasantness was increased with ortho-nasal odor presentation. In addition, for the creaminess intensity and texture liking enhancement, the observed effects were more pronounced with butter odor presentation at the lower concentration. Taken together, these findings suggested the importance of temporal congruency for cross-modal sensory enhancement in food flavor perception. The findings help to better understand flavor perception during oral processing of solid food, and add value for future development of foods with nutritional benefits. Key words: Cross-modal sensory enhancement; orthonasal; retronasal; cheese; texture; congruency
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Introduction Flavor is one of the most important attributes for food evaluation. Food flavor perception involves multisensory interaction in which signals from different sensory channels, including olfactory, gustatory, mechanical, trigeminal and even auditory sources merge and form a whole sensory percept (Seo and Hummel 2017). Sensory signals from different modalities often interact (enhancement or suppression) with each other and modulate the whole flavor perception. Odors not only contribute to the qualitative diversity of food, but also interact with other sensations and modulate the overall flavor perception. The most studied crossmodal sensory enhancement is between odor and taste, which often form the unitary flavor of food (Dalton et al. 2000), with a number of previous studies having shown odor enhancement by taste (Green et al. 2012; Welge-Lussen et al. 2009) or taste enhancement by odors (Labbe et al. 2006; Labbe et al. 2007; Sakai et al. 2001; Schifferstein and Verlegh 1996). The cross-modal sensory enhancement largely depends on the quality and temporal congruency of individual sensory stimuli. The quality congruency refers to the extent to which signals for distinct modalities could be considered attributes to the same object. For example, the salty- or sweet- congruent odor could enhance the saltiness and sweetness perception, respectively (Seo et al. 2013; Small et al. 2004). In the opposite direction, Green (2012) showed that sucrose, but not other tastants (NaCl, citric acid), significantly enhanced the perceived intensity of citral, vanillin, and furaneol - an strawberry odor. Quality congruency also influences the pleasantness, intensity and familiarity of the flavor perception. A recent study showed the odor-taste pairs were rated as more pleasant with increasing levels of congruency (Amsellem and Ohla 2016). In addition, the presence of a congruent taste significantly increased the localization of retronasal food odors to the tongue, known as the oral referral of retronasal odor perception (Fondberg et al. 2018; Lim et al. 2014; Lim and Johnson 2011; 2012). Neuroimaging studies also suggested a neural mechanism for the super additive effect of multisensory integration, in which certain brain areas (including insula, orbitofrontal cortex, amygdala and anterior cingulate cortex) respond to stimuli of different modalities (e.g. odor, taste or texture) and exhibit a larger response to their combinations than the sum of responses to each individual stimulus (de Araujo et al. 2003; Onuma et al. 2018; Small et al. 2004; Verhagen and Engelen 2006). The enhancement of perceptual as well as neural responses depends on familiarity and prior experiences with the stimulus (Frank and Byram 1988; Small et al. 2004). In addition, the quality congruency depends on the route of odor delivery, especially for foods. For instance, a number of studies reported the 3
enhancement of taste intensity by odor delivered via the retronasal route (Lawrence et al. 2009; Manabe et al. 2014; Stevenson et al. 1999). This is due to the fact that retronasal odors are more referred to the mouth to elicit flavor that represents known or potential foods (Lim and Johnson 2012). Apart from quality congruency, the congruency in the temporal dimension (e.g. timing of the delivery of sensory stimuli from different sensory modalities) is also important for multisensory enhancement (Isogai and Wise 2016). Holding a subthreshold concentration of saccharine in the mouth decreased detection thresholds for a sweet almond aroma, but odor thresholds were not affected when subjects expectorated the saccharine solution before sampling the odor (Pfeiffer et al. 2005). Recently, Kakutani and colleagues (Kakutani et al. 2017) compared the sweet taste intensity when a vanilla odor was presented synchronously with breathing via either orthonasal or retronasal route either before or after drinking the solution. Taste enhancement was observed only when the odor was presented retronasally and subjects exhaled after drinking the beverage, suggesting the importance of both the route of odor delivery and the temporal synchrony between odor and taste for the enhancement (Kakutani et al. 2017). Similar findings have been found for texture enhancement by odor. Retronasal aroma increased rated creaminess of dairy samples most when odor was presented during swallowing, less when presented while subjects manipulated the dairy sample in the mouth before swallowing, and not at all when the odor was presented while the mouth was filling (Bult et al. 2007). In another study, the enhancement of sweetness and bitterness by “sweet” and “bitter” odors was greatest with simultaneous presentation, and the enhancement was largely attenuated when the odor was presented before or after the delivery of taste with only one second of deviation (Isogai and Wise 2016). Food odor does not only have an impact on taste perception, but also on food texture. Previous research suggested that specific texture sensations such as creaminess, a highly desirable food property, are multi-modal percepts reflecting odor, taste, textural and, possibly, hedonic properties of foods (de Wijk et al. 2006). The interaction between odor and texture has been shown in previous studies (Hollowood et al. 2002; Pangborn et al. 1978). Food texture (e.g. creaminess or thickness) is also important for overall food sensory characteristics, especially for certain types of food such as milk products. It has been found that increased viscosity of beverages reduces retronasal odor intensity (Pangborn et al. 1978). Our previous work showed higher ratings for milk thickness and creaminess when butter-like odor was presented retronasally at the time of swallowing (Bult et al. 2007; Roudnitzky et al. 2011). 4
This pointed towards the temporal congruency of odor-texture enhancement in the late phase of oral processing. The first aim of the current study was to investigate the modulation of added odor on texture and flavor perceptions of a solid food - cheese. In addition, unlike previous research, the current study allowed subjects to chew the cheese ad libitum, trying to imitate eating situations in real life. A butter-like odor was presented at various stages of the eating cycle at the start of chewing, during chewing, and before swallowing, either through the orthonasal or retronasal route; multiple sensory attributes were rated. This study also tried to address the potential interaction between odor-texture enhancement with odor concentration and cheese type (e.g. fat level). We therefore included two concentrations of odor based on individual perceptual threshold and three types of cheese with varied fat content (high-fat, medium-fat and low-fat cheese). Materials and Methods Participants Twenty young healthy participants (12 females and 8 males) aged between 25 and 29 years took part in this study. Inclusion criteria were a normal sense of smell, as ascertained using the “Sniffin’ Sticks” test (Hummel et al. 1997), and self-reported regular consumption of Gouda cheese. The study was carried out in the Smell & Taste Clinic at the Department of Otorhinolaryngology of the TU Dresden, and the protocol was approved by the local Medical Ethical Committee (EK284122006). All participants were informed about the experimental procedure and provided informed written consent before participation. Odor stimuli The butter odor (Butter Buds Food Ingredients, Racine, WI, USA), a natural cream flavor, was used as odor stimulus. Two odor concentrations were selected for the study based on the individual threshold levels of the participants: the low concentration (LC) was just detectable for all subjects (5% above threshold - see below), whereas the high concentration (HC) was clearly detectable for all participants (twice the concentration of LC). Cheese stimuli The used cheeses were varieties of Gouda cheese ages less than two months. Gouda is the most popular type of Dutch cheese and accounts for approximately 50% of all Dutch cheeses. 5
Three Gouda cheese products (Friesland Foods, Meppel, The Netherlands) varying in fat level, i.e., low-fat (LF, 20% fat), medium-fat (MF, 30% fat), and high-fat (HF, 40% fat) cheeses, were used in this study. Using a cheese slicer (Genius, Limburg, Germany), each cheese sample was broken into bite-size cubes (16×16×12 mm). Procedure Participants took part in three sessions. In the first session, detection thresholds for butter odor were tested in an orthonasal way, using the method of ascending limits. Odorous stimuli of 1000 ms duration were presented to either left or right nostril (randomized selection) using a computer-controlled olfactometer (Burghart OM6b; Burghart, Wedel, Germany). Using the method of ascending limits the butter odor was delivered in ascending concentrations starting from the lowest concentration (5% v/v), and increased in steps of 5%. Participants were asked to answer “yes” or “no” whether an odor had been perceived or not. When participants perceived the odor at a certain concentration, they received the same concentration a second time. A threshold level was defined as the concentration where a given stimulus had been perceived twice in a row. The second and third sessions lasted approximately two hours each, during which all cheese stimuli were presented once in all experimental conditions. Participants were asked to chew each cheese cube ad libitum in the presence of either ortho- or retro-nasal odor at the low or high concentration level. The odor presentation followed the same procedure described previously (Bult et al. 2007). In the orthonasal condition (O), the odor stimulus was presented immediately after the cheese had been put into the mouth but before the onset of chewing (to mimic the natural situation where cheese is smelled ortho-nasally when the cheese is brought to the mouth). In the three retronasal conditions, the odor stimulus was presented retronasally at three different moments: at the start of chewing (R1), between the start and swallowing (R2), and during swallowing (R3). Oral chewing activity was measured using vibromyography (VMG) activity of the prelaryngeal, submandibular, buccal, and temporal muscles (de Wijk et al. 2008). VMG measurements allowed direct identification of the onsets of chewing and swallowing which served as triggers for odor delivery. The inter-stimulus interval between cheese stimuli was approximately 4 min to minimize adaptation. In addition to eight odor conditions (i.e., four instants of odor presentation × two odor concentrations), a control condition (C) was included without any odor presentation which was also applied with any of the three cheese stimuli. Therefore, the total number of stimulus conditions was 27 6
(i.e., 9 odor conditions × 3 cheese types) and each stimulus condition was tested in duplicate through the second and third sessions. Participants were asked to evaluate the intensities for cheese creaminess, butter note, overall flavor, and the pleasantness for cheese texture. Ratings for cheese sensory attributes were performed using the visual analogue scales (VAS): for intensity ratings the VAS ranged from 0 (not creamy / no butter note / no flavor) to 100 (very creamy / very strong butter note / very strong flavor), and for the texture pleasantness rating the VAS ranged from 0 (unpleasant) to 100 (pleasant) with a central marker indicating neutral.
Figure 1 Diagram showing the experimental procedure for one type of cheese under one odor stimulus concentration. Cells in grey indicate the timepoints for different conditions for odor stimuli and ratings for sensory attributes. Odor stimulus was presented orthonasally for 3 s after food intake and before chewing (O1). Odor stimulus was presented retronasally for 3 s at the three different instants: at the start of chewing (R1), half-way between chewing and swallowing (R2), or during swallowing (R3). Statistical analysis Data analysis was conducted using SPSS for WindowsTM (version 24.0, IBM SPSS Inc., Chicago, IL, USA), GraphPad Prism (Version 6, GraphPad Software, Inc. La Jolla, CA), and XLSTAT statistical software (Addinsoft, New York, NY, USA). To determine whether odor condition (i.e., O, R1, R2, R3, and C) could affect attribute intensities and texture likings of three types of cheese (i.e., LF, MF, and HF), a three-way analysis of variance (ANOVA), treating “odor condition” and “cheese type” as fixed effects and “participants” as a random effect, was performed as a function of odor concentration (i.e., L and H). Post-hoc comparisons between independent variables were performed using Tukey’s Honest Significant Difference (HSD) method. A statistically significant difference was defined as p < 7
0.05. To examine associations between odor condition (i.e., O, R1, R2, R3, and C) and attribute intensities and likings of cheese stimuli, principal component analysis (PCA) on covariance matrix was conducted using XLSTAT statistical software. Results Butter odor threshold The individual thresholds for butter odor are shown in Table 1. The averaged butter odor threshold was 14.75 (1.87), with 95% confidence interval (CI) 10.84 (lower CI) and 18.66 (higher CI) at 500-ms stimulation. The mean threshold was 9.25 (SEM 1.63), with the 95% CI 5.83 (lower CI) and 12.67 (upper CI) at 1000-ms stimulation. There was a significant effect of gender on threshold, showing that female participants were more sensitive to butter odor than male participants (F = 5.68, p = 0.03). There was no effect of nostril sides (F = 0.18, p = 0.68) or interaction between gender and nostril side (F = 0.18, p = 0.68) on butter odor threshold. Participants’ information and threshold levels are shown in the supplementary Table 1. Creaminess Low concentration level of butter odor There was no significant interaction between odor condition and cheese type in the ratings of creaminess intensity (F = 2.74, p = 0.22). The odor condition had a significant impact on creaminess perception (F = 2.74, p = 0.035). Post-hoc test showed that the creaminess intensity ratings in the R1 odor condition were greater than those in the R3 odor condition (p = 0.01). Creaminess intensities significantly differed with a fat level of cheese stimuli (F = 45.51, p < 0.001), with highest creaminess rating for HF, followed by MF and the LF cheese stimuli. High concentration level of butter odor There was no significant interaction between odor condition and cheese type in the ratings of creaminess intensity (F = 0.89, p = 0.53). Creaminess intensities were not significantly different as a function of odor condition (F = 0.14, p = 0.97), but differed in relation to the fat level of cheese stimuli (F = 51.32, p < 0.001), with highest creaminess ratings for HF, followed by MF and the LF cheese stimuli. 8
Figure 2: Mean ratings of creaminess intensity for cheese stimuli in the absence (control) or the presence of butter odor. Odor stimulus at either a low or a high concentration was presented via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. Butter note Low concentration level of butter odor There was no significant interaction between odor condition and cheese type in the intensity ratings of the butter note (F = 1.15, p = 0.34). Butter note intensities significantly differed by odor condition (F = 6.50, p < 0.001), with the butter note intensity being significantly higher in all odor conditions as compared to control conditions (i.e., no odor), as shown in Figure 2. In addition, perceived butter note intensity was highest when the odor was delivered during chewing (R2). Intensities of butter note during chewing (R2) was greater than those before chewing (i.e., orthonasal condition, “O”) and in the control condition (Figure 2). Intensity ratings of butter note were significantly greater in relation to the fat level of cheese stimuli (F = 11.29, p < 0.001), with highest butter note ratings for HF, followed by MF and the LF cheese stimuli. High concentration level of butter odor 9
There was no significant interaction between odor condition and cheese type in the intensity ratings of butter note (F = 0.63, p = 0.75). Butter note intensities were significantly different by odor condition (F = 6.24, p < 0.001). Similar to the trend at the lower concentration level of butter note, butter note intensities in the control condition (i.e., no odor) were significantly lower than other conditions with butter odor presentation, and butter note intensities in the R2 condition were greater than those in the O and control conditions (Figure 2). Intensity ratings of butter note significantly increased with the fat level of cheese stimuli (F = 7.09, p = 0.002), with highest butter note ratings for HF, followed by MF and the LF cheese stimuli.
Figure 3: Mean ratings of butter notes intensity for cheese stimuli in the absence (control) or the presence of butter odor. Odor stimulus at either a low or a high concentration was presented via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. Pleasantness of cheese texture Low concentration level of butter odor There was no significant interaction between odor condition and cheese type in the pleasantness ratings of cheese texture (F = 0.68, p = 0.71). Pleasantness ratings of cheese texture were significantly different as a function of odor condition (F = 2.86, p = 0.03), with higher ratings of texture pleasantness in the O condition than in the R3 condition; there were 10
no other pairwise differences between odor conditions. Pleasantness ratings of cheese texture significantly increased with a fat level of cheese stimuli (F = 11.10, p < 0.001), with highest texture liking for FF, followed by MF and the LF cheese stimuli. High concentration level of butter odor There was no significant interaction between odor condition and cheese type in the pleasantness ratings of cheese texture (F = 0.84, p = 0.57). Pleasantness ratings of cheese texture were not significantly different by odor condition (F = 0.27, p = 0.90). Pleasantness ratings of cheese texture significantly increased with a fat level of cheese stimuli (F = 10.26, p < 0.001), with highest texture liking for FF, followed by MF and the LF cheese stimuli.
Figure 4: Mean ratings of texture pleasantness for cheese stimuli in the absence (control) or the presence of butter odor. Odor stimulus at either a low or a high concentration was presented via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. Overall flavor Low concentration level of butter odor
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A significant interaction between odor condition and cheese type was observed in the intensity ratings of overall flavor of cheese stimuli (F = 2.48, p = 0.02). More specifically, a significant effect of odor condition on overall flavor intensity was present with MF cheese (F = 3.12, p = 0.02); the ratings for overall flavor intensity were significantly higher at O condition as compared to R1 (p = 0.03), but not with LF (F = 2.13, p = 0.09) or HF (F = 0.53, p = 0.72) cheese stimuli. There was no significant effect of odor condition (F = 0.29, p = 0.89) or cheese type (F = 2.60, p = 0.09) on intensity ratings of overall flavor.
Figure 5: Mean ratings of overal flavour intensity for cheese stimuli varied in their fat content (MF, medium-fat; HF, high-fat; LF, low-fat) in the absence (control) or the presence of butter odor presented at a low concentration via orthonasal (O1) or retronasal (R1, R2, and R3) pathways. Error bars represent standard error of the means. Mean ratings with different letters at either low or high concentration level represent a significant difference at p < 0.05. High concentration level of butter odor There was no significant interaction between odor condition and cheese type in the intensity ratings of overall flavor of cheese stimuli (F = 0.94, p = 0.48). Intensity ratings of overall flavor did not differ in relation to the odor condition (F = 1.27, p = 0.29) or the cheese type (F = 2.63, p = 0.09). Associations of odor condition with attribute intensity and liking
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Biplot representations of the principal component analysis (PCA) performed for the low and high odor concentration levels are shown in Figure 3. The first principal component (PC1) accounting for 64.09% and 79.22% of the total variance is related to the temporal congruency (timing of odor presentation), and separated butter note from other sensory attributes. The second component (PC2) accounted for 26.20% and 20.05% of the total variance and suggested an overall enhancement of the cheese sensory attributes by added odor. The PC1 in both low and high odor concentration conditions mainly represents information linked to butter note intensity. At both odor concentration levels, there was a positive association between butter note intensity and added odor via retronasal route especially at R2 (Figure 3A and 3B). When cheese was consumed in the presence of butter odor at a low concentration level, the creaminess intensities were more associated with retronasal odors presented at the onset of chewing (R1) (Figure 3A), however, the added odor (R1) at the high concentration had little impact on the creaminess intensity (Figure 3B). Additionally we saw more differentiation between attributes and conditions in the low compared to the high odor concentration.
Figure 6: Bi-plots of principal component analysis (PCA) showing the associations of four odor conditions with creaminess, butter note, and overall flavor intensities and texture pleasantness of cheese stimuli as a function of odor concentration level: low (A) and high (B) concentration levels of butter odor. Discussion
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The present study confirmed the effects of an added butter odor on perceived creaminess, butter note, total flavor and the texture pleasantness for cheese with different levels of fat contents. The odor presentations varied in pathways (either ortho- or retro-nasal) and timings (at start of chewing, during chewing or during swallowing). The results demonstrated enhancement of creaminess ratings and butter note intensity, as well as texture liking by the added odor which varied with timing of presentation, and cheese type (fat content). In addition, the observed effects were more pronounced when the odor was added at a lower odor concentration. The enhancement of perceived cheese attributes by added butter odor is in line with the temporal congruency for cross-modal sensory perceptions. First, creaminess ratings increased when the butter odor was presented retro-nasally at the start of chewing (R1). This finding is in line with the temporal congruency theory for cross-modal sensory integration, in which the enhancement of cheese sensory attributes by retronasal odors depends on a temporal binding window (Isogai and Wise 2016). This is the point when the cheese interacts with oral surface and saliva, and the initiation of the physical breakdown (de Wijk et al. 2006). Similar findings were observed for liquid dairy products (i.e. milk) (Bult et al. 2007). Other studies found higher ratings of fatty intensity without nose clips compared with nose clips on, indicating the role for retronasal odor perception on texture perception (Zhou et al. 2016). In addition, human neuroimaging study showed retronasal odor stimulation was related to brain activation at the base of the central sulcus, corresponding to the primary representation of the oral cavity, possibly reflecting that retronasal odors are referred to the mouth (Small et al. 2005). Another study reported the enhanced activation of the mechanosensory area in response to sweetened milk when a butter note odor was presented via retronasal route (Iannilli et al. 2014). Moreover, the textural and olfactory inputs converge in the insular cortex which serves as the neural mechanism for the cross-modal sensory enhancement (Rolls 2012; Small 2012). The butter note intensity peaked when the odor was presented retronasally while the cheese was being chewed but before swallowing (R2 condition). This timing is mainly followed by an exhalation where the volatile compounds travel to the olfactory receptor via the retronasal route (Roudnitzky et al. 2011). Butter note is mainly contributed by diacetyl which is released from the cheese during chewing (Curioni and Bosset 2002). This finding suggests that the butter note is perceived while the cheese is under oral processing and the key volatile and non-volatile compounds are released from the cheese-saliva bolus (Feron et al. 2014). As for the texture pleasantness, an increased rating was observed when butter odor was presented 14
orthonasally at the lower concentration. This mimics the situation in which the cheese odor reaches the consumers’ nose before chewing the cheese. This suggests an influence of odor on the expectation of texture pleasantness. Again, this finding is in line with previous findings showing that odors can affect texture attributes and vice versa (Bult et al. 2007). However, the enhancement of perceived cheese creaminess and overall flavor intensity was more pronounced when the butter odor was presented at the lower concentration. This might be due to the higher odor concentration being perceived as less pleasantness (Sano et al. 2002). Results from the current study suggested the enhancement of perceived cheese sensory attributes were dependent on the added odor concentration, with higher effectiveness at lower compared to higher butter odor concentrations. This was also reflected in a more differential pattern between attributes and conditions in the low compared to the high odor concentration in PCA result. It was possible that the higher odor concentration, twice as high as the detective threshold, evoked irritation, which may in turn diminish the effect of odor-taste enhancement. Besides, higher odor concentration may be also related to changed quality (Gross-Isseroff and Lancet 1988) or valence perceptions (Rouby et al. 2009). Previous studies have reported the taste enhancement by odor at relatively lower rather than higher concentration levels (Labbe et al. 2007; Seo et al. 2013). Findings from the current study may have implications for developing novel foods with nutritional benefits. For example, it has been shown that the oro-sensory cues (such as creaminess) increased the satiating effect of a protein-rich beverage (Bertenshaw et al. 2013). Thicker products were able to generate expectations that they are more filling compared to their thinner counterparts (Hogenkamp et al. 2011; McCrickerd et al. 2012). Moreover, stronger sensory attributes could also contribute to satiety through a top-down modulation of hormone release (Yeomans et al. 2016), which may reduce excessive consumption of high fat foods. Therefore, the odor-enhanced texture perception may help to formulate foods with With increased satiating properties, but without adding calories (de Graaf 2012). This provides insights to formulating food products with low calories density, while preserving pleasantness and having higher satiating properties (Campbell et al. 2017; Saint-Eve et al. 2009). However, results from the current study also indicate that odor enhancing is highly specific and depends on factors such as the fat content of the food, the type and concentration of the odor. The current study has some limitations. First, the study was performed in young participants with a narrow age range, in order to minimize potential effects of age on olfactory function, 15
and, hence, on sensory evaluation. However, the results may not be representative of the general population. The participants were not trained so that individual differences regarding the interpretation of certain sensory attributes may confound the results. For example, while flavor is commonly known as the integration of taste, aroma, and trigeminal sensations, it is often confused with orthonasal olfactory perception; evaluation of selected sensory attributes in the current study emerged from integrated sensations of visual, olfactory, gustatory, and tactile cues (Chen and Eaton 2012). A group of experienced panellists would make the findings more reliable. Second, since the study used a single odorant with butter note, it is possible that the effect of butter odor is potent and specific for certain sensory attributes; it may be weak for others, given the complexity of cheese flavor. Future study could use other key odors derived from cheese that contribute to certain sensory characteristics. Third, although we controlled the timing of odor delivery, the oral processing was ad libitum which may result in different levels of flavor release between conditions. Besides, 5% of butter odor was assigned for the threshold level for most of the participants, which also the lowest concentration level used for the threshold testing. Therefore, it was possible that the actual threshold level was below than 5%, which may result in different outcomes. Lastly, tiredness due to long testing duration and satiety effect with cheese consumption over time may have impacted on the results shown here. In conclusion, the current study adds to the increasing knowledge that sensory perception can be modified substantially by adding an odor which is an expression of the intimate connection between all the sensory channels involved in flavor perception.
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Influences of odor concentration, delivery route and timing on cheese sensory attributes were studied.
Retronasal odor added during chewing enhanced perceived intensity of cheese creaminess and butter note.
Observed effects were more pronounced with butter odor presentation at the lower concentration.
Qualitative and temporal congruencies are important for cross-modal sensory enhancement.
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