Oral shear stress predicts flavour perception in viscous solutions

Conformational entropy of hyaluronic acid contributes to taste enhancement

Natural taste/flavor enhancers are essential ingredients that could potentially address condiments overconsumption. For the first time, we report that hyaluronic acid (HA) could modulate taste perception, governed by the dynamic interactions among taste compounds, mucin, and HA. Various conformations of HA impact taste perception. The high molecular weight (Mw) of 1090 kDa HA inhibits the sense of taste due to its increased viscosity, which hinders the penetration of Na⁺ into the mucin layer. HA with low and medium Mw (100 kDa, 400 kDa) could enhance taste perception. Isothermal titration calorimetry analysis confirms the stronger binding between mucin and HA. The intensity of their interaction increases as the Mw of HA increases from 8 kDa to 400 kDa. Quartz crystal microbalance with dissipation characterization further indicates that the rigid conformation of 100 kDa HA facilitates the binding of Na⁺ with taste receptors, thereby enhancing taste perception. The flexible conformation of 400 kDa HA may conceal the taste receptor cells, reducing taste enhancement. Our work advances the understanding of conformational entropy of natural mucoadhesion and mucopenetration polymers, which lays the foundation for their potential use as taste enhancers.

The Impact of Vanilla and Lemon Aromas on Sensory Perception in Plant-Based Yogurts Measured with Static and Dynamic Methods

The application of cross-modal interaction is a potential strategy to tackle the challenges related to poor sensory properties, such as thin mouthfeel, in plant-based yogurts. Thus, we aim to study the influence of aroma compounds possibly congruent with sweetness on the perceived sensory profile. Descriptive analysis and temporal dominance of sensations (n = 10 × 4) with a trained panel were conducted with and without a nose clip. One unflavored sample and samples flavored with either lemon or vanilla aromas were included (vanilla; 0.05%; 0.1%; lemon: 0.025%; 0.05%). Odor intensity, thick, sticky, and melting sensation, sweetness, and grain-like flavor were evaluated on an unstructured 10-cm line scale with anchors and reference samples. The results demonstrate how vanilla and lemon aromas suppressed grain-like flavor and enhanced odor intensity and sweetness. The following order was detected among samples in perceived sweetness intensity: unflavored < lemon < vanilla. The two sessions with and without nose clip differed statistically in sweetness, highlighting that the aromas impacted the perceived sweetness but not the mouthfeel in vanilla samples. The study suggests that congruent aromas could modify the perceived sweetness in plant-based yogurts; however, aroma or perceived sweetness does not impact the mouthfeel in plant-based yogurts. While the odor−taste interaction in such products is evident, the study highlights that aroma compounds alone do not modify mouthfeel.

The role of viscosity in flavor preference: plasticity and interactions with taste

The brain combines gustatory, olfactory, and somatosensory information to create our perception of flavor. Within the somatosensory modality, texture attributes such as viscosity appear to play an important role in flavor preference. However, research into the role of texture in flavor perception is relatively sparse, and the contribution of texture cues to hedonic evaluation of flavor remains largely unknown. Here, we used a rat model to investigate whether viscosity preferences can be manipulated through association with nutrient value, and how viscosity interacts with taste to inform preferences for taste + viscosity mixtures. To address these questions, we measured preferences for moderately viscous solutions prepared with xanthan gum using 2-bottle consumption tests. By experimentally exposing animals to viscous solutions with and without nutrient value, we demonstrate that viscosity preferences are susceptible to appetitive conditioning. By independently varying viscosity and taste content of solutions, we further show that taste and viscosity cues both contribute to preferences for taste + viscosity mixtures. How these 2 modalities are combined depended on relative palatability, with mixture preferences falling in between component preferences, suggesting that hedonic aspects of taste and texture inputs are centrally integrated. Together, these findings provide new insight into how texture aspects of flavor inform hedonic perception and impact food choice behavior.

Thickened Liquids Using Pureed Foods for Children with Dysphagia: IDDSI and Rheology Measurements

Children with dysphagia, or swallowing disorder, are at an increased risk for developing respiratory compromise, failure to thrive, and aversion. Thickened liquids can be recommended for children with dysphagia, if shown to be effective on instrumental examination and if strategies/interventions with thin liquids are not successful. Thickened liquids have many benefits, including creating a more cohesive bolus, slowing oropharyngeal transit time, and reducing aspiration. However, preparing thickened liquids with commercially available thickeners can result in poor compliance due to concerns regarding taste, texture, accessibility, cost, thickness variability, and potential negative impact of these substances on a child's immature digestive tract. The purpose of this study was to determine if liquids could be successfully thickened with widely available, commercial pureed foods, and to assess how these mixtures compare to starch and gum based thickening agents. The International Dysphagia Diet Standardisation Initiative (IDDSI) flow test was performed for each sample of puree thickened liquids, gum based thickened water, and cornstarch based thickened water. In addition, rheology testing was performed on each category of the samples to measure viscosity at various shear rates and temperatures, and to assess the presence of yield stress. Results revealed that liquids thickened with smooth textured purees were comparable to commercial starch and gum based thickeners, and may be offered as a viable alternative.

Impact of pulsation rate and viscosity on taste perception - Application of a porous medium model for human tongue surface

BACKGROUND

Temporal dynamics may importantly modulate sensory perception, including taste. For example, enhanced perceived taste intensity is often observed when tastant concentration is fluctuating in pulses. The perceived intensity is higher than that of the solutions with a same averaged, but constant concentrations. Meanwhile, taste intensity often decreases with increase of tastant viscosity, despite no changes to the stimuli concentration. The mechanisms to these phenomena are not well understood, in part due to the complicated transport process of tastant through papillae, taste pores, etc. to reach the taste receptors, a cascade of events that are difficult to quantify.

METHOD

We computationally modeled the human tongue surface as a porous micro-fiber medium, extending a previous study and exposed it to pulsatile tastant solution (0.2 and 0.4Hz) with various added viscosity (~0.0011-~0.09 Pa⋅s).

RESULTS

Our simulation revealed that the stimuli concentration within the papillae structure increase with pulsed stimulation, especially those with a longer period (16% increase at 0.4Hz and 23% at 0.2Hz compared to continuous stimuli) and decrease (-6%) with added viscosity. The trend matched well with measured taste perception to sucrose added apple juice in the literature (R² > 0.97 for both low and high viscosity stimuli series). Decreased diffusivity due to the increase in viscosity, however, was not a major factor underlying this process.

CONCLUSION

This study re-affirms the validity and accuracy of modeling human tongue surface as a porous medium to investigate taste stimuli transport processes and such peripheral transport dynamics may have significant effects on taste perception.

Taste of time: A porous-medium model for human tongue surface with implications for early taste perception

Most sensory systems are remarkable in their temporal precision, reflected in such phrases as “a flash of light” or “a twig snap”. Yet taste is complicated by the transport processes of stimuli through the papilla matrix to reach taste receptors, processes that are poorly understood. We computationally modeled the surface of the human tongue as a microfiber porous medium and found that time-concentration profiles within the papilla zone rise with significant delay that well match experimental ratings of perceived taste intensity to a range of sweet and salty stimuli for both rapid pulses and longer sip-and-hold exposures. Diffusivity of these taste stimuli, determined mostly by molecular size, correlates greatly with time and slope to reach peak intensity: smaller molecular size may lead to quicker taste perception. Our study demonstrates the novelty of modeling the human tongue as a porous material to drastically simplify computational approaches and that peripheral transport processes may significantly affect the temporal profile of taste perception, at least to sweet and salty compounds.

Taste perception is an important gateway for food selection, food intake, energy and nutrition balance–as world is facing epidemic of obesity and diabetes. Information conveyed via the taste system provide crucial behavior choices, e.g. in identifying edible and nutritious food source, driving hedonic evaluation and craving, as well as avoiding poisonous substances. Thus, the interest to understand early taste responses is important, not only for basic science, but also for clinical and public health applications.

Ternary Cross-Modal Interactions between Sweetness, Aroma, and Viscosity in Different Beverage Matrices

Sugar reduction in food and beverage products involves several challenges. Non-nutritive sweeteners may give unwanted off-flavors, while sugar-reduced products often lack mouthfeel. To overcome this, the addition of aroma to increase sweetness through cross-modal interactions, and the addition of hydrocolloids such as pectin to increase viscosity, have been suggested as strategies to aid sugar reduction. However, viscosity has been shown to decrease both taste and aroma intensities. An increase in viscosity may thereby affect the use of aromas as sweetness enhancers. Additionally, the effects of aromas and hydrocolloids on sweetness intensity and mouthfeel depend on the food matrix involved. The present study investigated cross-modal aroma-sweetness-viscosity interactions in two beverage matrices: water and apple nectar. The perceptual effects of vanilla aroma (0-1 mL/kg), sucrose (2.5%-7.5% w/w) and pectin (0%-0.3% w/w) were studied in both matrices. For each matrix, cross-modal interactions were analyzed with descriptive analysis using a trained sensory panel. The effect of vanilla aroma on sweetness intensity was found to be higher in apple nectar compared to in water. Furthermore, pectin affected neither taste, aroma, nor the cross-modal effects of aroma on taste in either of the matrices. These results indicate that pectin, in the studied range of concentrations, may be used to improve mouthfeel in sugar-reduced beverages, without compromising taste or aroma perception.

Viscosity drives texture perception of protein beverages more than hydrocolloid type

Hydrocolloids are added to alter rheological properties of beverages but have other properties that can contribute to overall taste and texture perception. In this study, tapioca starch and λ-carrageenan were used to determine how hydrocolloid type, viscosity level (4-6 mPa·s, 25-30 mPa·s, and 50-60 mPa·s at 50 s^-1 ), and complexity of the system (aqueous, skim milk, or whole milk) influence sensory taste and texture of fluids. All fluids were shear thinning; however, skim milk and whole milk solutions that contained carrageenan had much higher low shear viscosity and lower high shear viscosity than those with starch. There was a significant effect of viscosity level on sensory perception of consistency, creamy/oily, mouthcoating, and residual mouthcoating in aqueous, skim milk, and whole milk beverages, and a weak effect of hydrocolloid type. However, normalizing creamy/oily, paste, and mouthcoating against sensory consistency removed the effect of hydrocolloid type. Flavors (cream, cooked, cardboard, and melon/cardboard) were associated with the type of hydrocolloid and milk protein ingredient. Temporal dominance of sensations showed that samples exhibit similar temporal sensory profiles, although the addition of hydrocolloids enhanced dominance of creaminess even in samples without fat. Hydrocolloid type did not significantly influence mouthcoating or the persistence of astringency. Additionally, increasing viscosity from 3 to 74 mPa·s at 50 s^-1 did not suppress perceived sweet or salty taste. The results suggest that in fluid systems with viscosity levels typically found in beverages, textural properties are determined by viscosity and independent of the type of hydrocolloid.

A comparison of the sensory and rheological properties of different cellulosic fibres for food

The impact of different cellulosic microstructures formed by highly entangled fibre networks was studied for food applications as dietary fibre. This paper reports the impact of the microstructure on the rheological and sensory behaviour of the aqueous suspensions of particulate and fibrillated forms of softwood cellulosic fibres, and was compared with citrus fibres. An aqueous suspension of cellulosic fibres shows stable viscoelastic gel-like behaviour as a function of frequency. The particulate form of cellulosic fibres showed the lowest shear viscosity as compared with the entangled network system at comparable concentrations. To provide further insight into the relationship between the structure of cellulosic fibre and taste (salt) perception, an aqueous suspension with matched shear viscosities were studied. A hypothesis to explain why softwood cellulosic fibre (CTE) with an entangled network structure prolongs the taste perception is presented.

Factors affecting the ortho- and retronasal perception of flavors: A review

Flavor perception is a highly individual sensation, and is impacted by a number of factors. Olfaction is a critical element in fully experiencing flavor. In this review, we explore the differences between orthonasal (sniff) versus retronasal (mouth) olfaction, and provide a comprehensive summary of recent publications in this arena. Here we explore the complexities of flavor perception, including the role that select flavors and media have on identification and localization. We also discuss some common neural imaging techniques used in this field, as odorants activate different neural responses in diverse areas of the brain, as well as the different stimulation patterns derived from perceiving food and nonfood related odorants. The information provided will be useful for sensory scientists and industry alike for the development of novel food and beverages that positively impact the consumer experience.

Effect of hydrocolloid on rheology and microstructure of high-protein soy desserts

Due to the rheological and structural basis of texture perceived in semisolid foods, the aim of this work was to study the effects of two thickening agents, on rheology and microstructure of soy protein desserts. As rheological parameter values may not be enough to explain the possible perceived texture differences, the effect of composition on two instrumental indexes of oral consistency (apparent viscosity at 50 s(-1) and complex dynamic viscosity at 8 Hz) was also studied. Samples were prepared at two soy protein isolate (SPI) concentrations (6 and 8 % w/w), each with four modified starch concentrations (2, 2.5, 3 and 3.5 % w/w) or four Carboxymethyl cellulose (CMC) concentrations (0.3, 0.5, 0.7 and 0.9 % w/w). Two more samples without added thickener were prepared as control samples. The flow curves of all systems showed a typical shear-thinning behaviour and observable hysteresis loops. Control sample flow fitted well with the Ostwald-de Waele model and the flow of samples with thickener to the Herschel-Bulkley model. Viscoelastic properties of samples ranged from fluid-like to weak gel, depending on thickener and SPI concentrations. Starch-based samples exhibited a globular structure with SPI aggregates distributed among starch granules. In CMC-based samples, a coarse stranded structure with SPI aggregates partially embedded was observed. Variation of the two thickness index values with composition showed a similar trend with good correlation between them (R(2) = 0.92). Soy desserts with different composition but with similar rheological behaviour or instrumental thickness index values can be obtained.

Properties of oil/water emulsions affecting the deposition, clearance, and after-feel sensory perception of oral coatings

The aims of this study were to investigate the influence of (i) protein type, (ii) protein content, and (iii) viscosity of o/w emulsions on the deposition and clearance of oral oil coatings and after-feel perception. Oil fraction (m(oil)/cm(2)(tongue)) and after-feel perception differed considerably between emulsions which do not flocculate under in mouth conditions (Na-caseinate) and emulsions which flocculate under in mouth conditions (lysozyme). The irreversible flocculation of lysozyme stabilized emulsions caused slower oil clearance from the tongue surface compared to emulsions stabilized with Na-caseinate. Protein content had a negative relation with oil fraction for lysozyme stabilized emulsions and no relation for Na-caseinate stabilized emulsions immediately after expectoration. Viscosity differences did not affect oil fraction, although the presence of thickener decreased deposition of oil on tongue. We conclude that after-feel perception of o/w emulsions is complex and depends on the deposited oil fraction, the behavior of proteins in mouth, and thickeners.

Oral texture influences the neural processing of ortho- and retronasal odors in humans

Eating implies mutual interactions between different senses. In the present work we aimed at studying relations between food texture and food odor, using both psychophysical and imaging techniques. Eighteen right-handed healthy human subjects participated to both behavioral and fMRI sessions. Fresh, sweetened milk and a more thickened version were delivered orally; in addition, a buttery-cream aroma was presented ortho- or retronasally. Stimuli were applied using a gustometer and or an air-dilution olfactometer, both computer-controlled. In each session subjects rated separately odor-, taste- and thickness intensities of the stimuli. The behavioral data show that odors, presented through either retro- or orthonasal path, induce a significant flavor enhancement with respect to the no-odor condition. Brain functional data indicated a significant enhancement of the activation of olfactory eloquent areas in favor of ortho-nasal odor presentation while activations of mechanosensory areas were favored by the retro-nasal odor route. As effect of oral stimuli we found a significant correlation between the texture intensity rating vs. the BOLD signal in the supplementary motor area, known to drive subconsciously primed movement, putatively associated in this case with the tongue movement required with the handling of the stimulus. Moreover, we found inhibition of the signal in different sensory specific areas as an effect of the mutual interaction between stimulus qualities. In conclusion, ortho- and retronasal odors differentially affect the neural processing of the texture of oral stimuli.

A comparison of the sensory and rheological properties of molecular and particulate forms of xanthan gum

A particulate form of xanthan gum was prepared by extrusion cooking. The temperature dependence of the viscosity of this form shows similarities to starch with an increase in viscosity to a maximum with increasing temperature as a result of the swelling of the particles. The rheology and mixing behaviour with water of the particulate and conventional molecular forms of xanthan were compared with a modified starch. The particulate xanthan products mixed rapidly with water in a similar way to ungelatinised starch, whereas conventional molecular xanthan systems mixed poorly. Using an experienced sensory panel, model tomato products thickened with the three systems were compared at equal shear viscosities. The panel could not discriminate between the tomato flavour of the three products, but found that the xanthan products were perceived as being significantly thicker. These observations were consistent with previous work. Salt perception for both xanthan products was poorer than for the starch thickened systems. A hypothesis to explain why xanthan does not fit into the previously postulated link between mixing and perception is presented.

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Particulate form of xanthan was made by extrusion, no degradation of biopolymer.

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Suspension of the particulate form of xanthan mixed well with water.

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No difference in flavour of soups thickened by starch or two forms of xanthan.

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No link between the mixing behaviour and flavour perception for xanthan.

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Suggested that xanthan interacts in a specific way with saliva.

Dairy-Based Emulsions: Viscosity Affects Fat Difference Thresholds and Sweetness Perception

In complex emulsions, viscosity or viscosity-associated sensory attributes such as creaminess are important for quality assessment and product differentiation. Two sets of emulsions with fat or locust bean gum content being varied at seven levels were developed; the two emulsions at each level had similar apparent viscosity. Additionally, sugar concentration was kept constant either with respect to total emulsion, or with respect to the aqueous phase. Series of two-alternative forced choice tests were performed with one constant stimulus, and just noticeable differences were calculated using probability regression. The results show that, when viscosity was not compensated, it was easy for the subjects to (a) distinguish emulsions with different fat content when the fat content was addressed in the question, and to (b) distinguish emulsions with different fat or locust bean gum content when creaminess was addressed. For the latter descriptor, it is of minor importance whether viscosity is altered by fat content or a thickener. Weber fractions that were calculated for viscosity were approximately 0.20. The quantitative effects of viscosity on sweetness, however, depend on how product rheology was modified.

Influence of texture on the perception of saltiness in wheat bread

As a basis for sodium reduction in bread, the influence of crumb texture on the intensity of saltiness and the release of sodium ions during chewing was investigated. A coarse-pored bread crumb was created by extending the proofing time (90/120 min vs 20/40 min as control), whereas the omission of proofing resulted in a fine-pored crumb (0/0 min). A significantly faster sodium release from the coarse-pored bread compared to the fine-pored bread (constant sample weight) was measured in-mouth and in a mastication simulator. This explained the significantly enhanced salty taste of the 90/120 min bread. Corresponding experiments with constant sample volumes revealed a significantly enhanced saltiness despite similar amounts of extracted sodium during the first seconds of chewing. Therefore, saltiness was influenced both by the velocity of sodium release and by crumb texture. Appropriate modification of crumb texture thus leads to enhanced saltiness, suggesting a new strategy for salt reduction in bread.

Orosensory and Homeostatic Functions of the Insular Taste Cortex

The gustatory aspect of the insular cortex is part of the brain circuit that controls ingestive behaviors based on chemosensory inputs. However, the sensory properties of foods are not restricted to taste and should also include salient features such as odor, texture, temperature, and appearance. Therefore, it is reasonable to hypothesize that specialized circuits within the central taste pathways must be involved in representing several other oral sensory modalities in addition to taste. In this review, we evaluate current evidence indicating that the insular gustatory cortex functions as an integrative circuit, with taste-responsive regions also showing heightened sensitivity to olfactory, somatosensory, and even visual stimulation. We also review evidence for modulation of taste-responsive insular areas by changes in physiological state, with taste-elicited neuronal responses varying according to the nutritional state of the organism. We then examine experimental support for a functional map within the insular cortex that might reflect the various sensory and homeostatic roles associated with this region. Finally, we evaluate the potential role of the taste insular cortex in weight-gain susceptibility. Taken together, the current experimental evidence favors the view that the insular gustatory cortex functions as an orosensory integrative system that not only enables the formation of complex flavor representations but also mediates their modulation by the internal state of the body, playing therefore a central role in food intake regulation.

Effects of pulsation rate and viscosity on pulsation-induced taste enhancement: new insights into texture-taste interactions

Oral stimulation with high-tastant concentrations that are alternared with low-tastant concentrations or water rinses (pulsatile stimulation) results in taste intensity ratings that are higher than continuous stimulation with the same average tastant concentration. This study tested the combined effects of taste pulsation rate and viscosity on pulsation-induced taste enhancement in apple juice. According to a tastant-kinetics hypothesis, less pulsation-induced taste enhancement is expected at enhanced pulsation rates in the high-viscous proximal stimulus compared to lower viscous stimuli. High-concentration sucrose apple juice pulses and low-concentration sucrose apple juice intervals were alternated at different pulsation periods (pulse + interval in seconds) every 2.5 s (period length = 5 s) or every 1.25 s (period length = 2.5 s). Pulsed stimuli were presented at two viscosity levels by the addition of pectin (0 and 10 g/L). Sweetness intensities of pulsed stimuli were compared to a continuous reference of the same net but nonalternating sucrose concentration. Sweetness ratings were higher for pulsatile stimuli than for continuous stimuli. In low-viscous stimuli, enhancement depended on the pulsation period and peaked at 5 s periods. In high-viscous stimuli, the same enhancement was observed for both pulsation periods. These results contradict a tastant-kinetics hypothesis of viscosity-induced taste suppression because impaired tastant kinetics by viscosity would predict the opposite: lower pulsation-induced taste enhancement for viscous stimuli, especially at higher pulsation rates. Instead, these observations favor an explanation based on perceptual texture-taste interactions, which predict the observed independence between viscosity and pulsation rate.