Tracey Hollowood

Perception of taste intensity in solutions of random-coil polysaccharides above and below c∗

Sensory paired comparison tests were used to study differences in taste intensity in solutions of hydroxypropylmethyl cellulose (HPMC) at concentrations above (1.0% w/w) and below (0.2% w/w) c*, the coil-overlap concentration (the point at which viscosity changes abruptly with increasing thickener). The sweetness intensities of aspartame (250 ppm), sucrose (5% w/w), fructose (4.5% w/w) and neohesperidin dihydrochalcone (39 ppm) and the saltiness of sodium chloride (0.35%) were all found to be significantly reduced in the more viscous HPMC solution. There was no significant effect of HPMC concentration on the acidity of citric acid (600 ppm) or the bitterness of quinine hydrochloride (26 ppm). The sweetness intensities of sucrose and aspartame were likewise investigated in two further hydrocolloid solutions, guar gum and λ-carrageenan. Experiments were designed so that the ratios of the thickener concentrations (above and below c*) to their measured c* values remained constant. The sweetness of sucrose was found to be significantly reduced in the more viscous guar gum solution (P<0.05) and that of aspartame was reduced in the λ-carrageenan above c* (P<0.001). A multiple paired comparison design was used to show that the perceived sweetness of 6.5% sucrose in 1.0% HPMC did not differ significantly from that of 5% sucrose in 0.2% HPMC. The magnitude of effect with aspartame was broadly analogous.

The cortical response to the oral perception of fat emulsions and the effect of taster status

The rewarding attributes of foods containing fat are associated with the increase in fat consumption, but little is known of how the complex physical and chemical properties of orally ingested fats are represented and decoded in the brain nor how this impacts feeding behavior within the population. Here, functional MRI (fMRI) is used to assess the brain response to isoviscous, isosweet fat emulsions of increasing fat concentration and to investigate the correlation of behavioral and neuroimaging responses with taster status (TS). Cortical areas activated in response to fat, and those areas positively correlated with fat concentration, were identified. Significant responses that positively correlated with increasing fat concentration were found in the anterior insula, frontal operculum and secondary somatosensory cortex (SII), anterior cingulate cortex, and amygdala. Assessing the effect of TS revealed a strong correlation with self-reported preference of the samples and with cortical response in somatosensory areas [primary somatosensory cortex (SI), SII, and midinsula] and the primary taste area (anterior insula) and a trend in reward areas (amygdala and orbitofrontal cortex). This finding of a strong correlation with TS in somatosensory areas supports the theory of increased mechanosensory trigeminal innervation in high 6-n-propyl-2-thiouracil (PROP) tasters and has been linked to a higher risk of obesity. The interindividual differences in blood oxygenation level-dependent (BOLD) amplitude with TS indicates that segmenting populations by TS will reduce the heterogeneity of BOLD responses, improving signal detection power.

Taste-aroma interactions in a ternary system: a model of fruitiness perception in sucrose/acid solutions.

Cross-modal interactions between aroma, sweetness, and acidity were studied. A series of samples was presented to trained panelists who assessed strawberry flavor intensity using magnitude estimation with a reference modulus. The delivery of aroma stimuli from the different solutions was measured by monitoring exhaled breath using atmospheric pressure chemical ionization-mass spectrometry to determine whether there were any physicochemical effects on volatile release; no significant differences were noted. Three-dimensional predictive models were built to describe perceived strawberry flavor intensity as a function of concentrations of sucrose, acid, and volatiles. Analysis of the data identified two groups of panelists with different responses: For Group 1, increasing sucrose and/or acid levels also increased the perceived flavor intensity. For Group 2, changing sucrose concentrations had little effect, but increasing acid and/or volatile levels did. The results show different effects of organic and inorganic acids on perception, as well as clear interactions between the modalities of taste (sugar and acid) and aroma. The clustering of panelists’ responses suggests that this phenomenon may depend on prior associations between the fruity flavor and the tastants.

Prior Consumption of a Fat Meal in Healthy Adults Modulates the Brain’s Response to Fat

Background: The consumption of fat is regulated by reward and homeostatic pathways, but no studies to our knowledge have examined the role of high-fat meal (HFM) intake on subsequent brain activation to oral stimuli. Objective: We evaluated how prior consumption of an HFM or water load (WL) modulates reward, homeostatic, and taste brain responses to the subsequent delivery of oral fat. Methods: A randomized 2-way crossover design spaced 1 wk apart was used to compare the prior consumption of a 250-mL HFM (520 kcal) [rapeseed oil (440 kcal), emulsifier, sucrose, flavor cocktail] or noncaloric WL on brain activation to the delivery of repeated trials of a flavored no-fat control stimulus (CS) or flavored fat stimulus (FS) in 17 healthy adults (11 men) aged 25 ± 2 y and with a body mass index (in kg/m2) of 22.4 ± 0.8. We tested differences in brain activation to the CS and FS and baseline cerebral blood flow (CBF) after the HFM and WL. We also tested correlations between an individual’s plasma cholecystokinin (CCK) concentration after the HFM and blood oxygenation level–dependent (BOLD) activation of brain regions. Results: Compared to the WL, consuming the HFM led to decreased anterior insula taste activation in response to both the CS (36.3%; P < 0.05) and FS (26.5%; P < 0.05). The HFM caused reduced amygdala activation (25.1%; P < 0.01) in response to the FS compared to the CS (fat-related satiety). Baseline CBF significantly reduced in taste (insula: 5.7%; P < 0.01), homeostatic (hypothalamus: 9.2%, P < 0.01; thalamus: 5.1%, P < 0.05), and reward areas (striatum: 9.2%; P < 0.01) after the HFM. An individual’s plasma CCK concentration correlated negatively with brain activation in taste and oral somatosensory (ρ = −0.39; P < 0.05) and reward areas (ρ = −0.36; P < 0.05). Conclusions: Our results in healthy adults show that an HFM suppresses BOLD activation in taste and reward areas compared to a WL. This understanding will help inform the reformulation of reduced-fat foods that mimic the brain’s response to high-fat counterparts and guide future interventions to reduce obesity.

Does Fat Alter the Cortical Response to Flavor

Understanding the impact of fat in the oral cavity on the cortical response to flavor may aid the design of healthier low fat products which are acceptable to the consumer. However, varying fat content affects physicochemical and sensory properties, making it difficult to isolate the impact of the fat itself. The objective of this study was to investigate the interaction between fat and the cortical response to flavor, using a model emulsion system that enabled confounding factors, such as changes in volatile release and viscosity, to be controlled. Initial sensory and volatile release studies were performed to formulate four fruity emulsion samples, all iso-sweet and iso-thick, for use in the functional magnetic resonance imaging study: an unflavored fat emulsion; a flavored no-fat stimulus; and two further flavored fat emulsions, one iso-volatile release and one iso-perceived in fruit flavor intensity compared with the no-fat stimulus (the former containing less volatile). Stimuli were found to activate a large network of brain areas including the somatosensory cortices (SI and SII); anterior, mid, and posterior insula; anterior cingulate cortex amygdala, and thalamus. Overall, the flavored, no-fat stimulus led to increased activation compared with flavored and unflavored fat emulsions in areas relating to reward, taste, aroma, and somatosensory processing. Sensory data indicated that the only perceivable difference between the no-fat stimulus and fat emulsions was in the level of the oily/greasy film/residue left in the mouth which the panel termed “oiliness,” indicating this to be an important stimulus for the presence of fat in the oral cavity in these samples. The dampening effect of fat on cortical activity was somewhat reduced by increasing the volatile component of the stimulus without changing the perceived flavor.