Thermal taster status: Temperature modulation of cortical response to sweetness perception.

Temperature is known to impact taste perception, but its reported effect on sweet taste perception in humans is inconsistent. Here, we assess whether thermal taste phenotype alters the temperature modulation of the brains' response to sweet samples and sweet taste perception. Participants (n = 24 balanced for thermal tasters (TT) and thermal non-tasters (TnT), 25 ± 7 years (mean ± SD), 10 males) underwent a thermal taste phenotyping session to study responses to cooling and warming of the tongue using a thermode. In a separate session, functional Magnetic Resonance Images (fMRI) were collected during sweet samples (87 mM sucrose) delivery at two temperatures ('cold' (5 ± 2 °C) and 'ambient' (20 ± 2 °C)) and the perceived sweetness intensity rated.In the phenotyping session, TTs had heightened perceptual temperature sensitivity to cooling and warming of the tongue using a thermode compared to TnTs. Although there was no significant effect during the fMRI session, the fMRI response to the 'cold sweet' sample across all participants was significantly increased in anterior insula/frontal operculum and mid-insula compared to the 'ambient sweet' sample, likely to reflect the perceptual difference to temperature rather than taste perception. TTs showed significantly increased fMRI activation patterns compared with TnTs and an interaction effect between thermal taster status and sample temperature, with TTs showing selectively greater cortical responses to 'cold sweet' samples compared to TnTs in somatosensory regions (SI and SII).The increase in cortical activation in somatosensory cortices to the 'cold sweet' stimulus correlated with perceptual ratings of temperature sensitivity to the thermode. The results highlight the importance of investigating the effects of thermal taster phenotype across a range of temperatures representing the reality of consumer consumption to beverages.

Understanding fat, proteins and saliva impact on aroma release from flavoured ice creams.

The release profile of fourteen aroma compounds was studied in ice cream samples varying in fat and protein, both in level and type. In vitro aroma release was monitored by solid phase micro-extraction gas chromatography using an innovative saliva reactor, which imitated human chewing under temperature control. The results showed that the effect of the fat type on aroma release was smaller than that of fat level. Ice creams with low fat level released more hydrophobic aroma compounds than ice creams with high fat level. At low fat level more aroma compounds were released from ice creams with lower protein content. At high fat level a small increase of aroma release was observed by the addition of saliva, which was explained by a salting out effect, due to the presence of proteins and salts in the saliva. These findings confirmed that the interactions between salivary proteins and aroma compounds occurring in aqueous solutions are not observed in emulsions.

Dynamic in vivo mapping of model moisturiser ingress into human skin by GARfield MRI.

We describe the development of in vivo one-dimensional MRI (profiling) using a GARField (Gradient At Right angles to Field) magnet for the characterisation of side-of-hand human skin. For the first time and in vivo, we report measurements of the NMR longitudinal and transverse relaxation parameters and self-diffusivity of the upper layers of human skin with a nominal spatial resolution better than 10 µm. The results are correlated with in vivo confocal Raman spectroscopy measurements of water concentration and natural moisturiser factors, and discussed in terms of known skin biology and microstructure of the stratum corneum and viable epidermis. The application of model moisturiser solutions to the skin is followed and their dynamics of ingress are characterised using the MRI methodology developed. Selected hydrophilic and lipophilic formulations are studied. The results are corroborated by standard in vivo measurements of transepidermal water loss and hydration status. A further insight into moisturisation mechanisms is gained. The effect of two different penetration enhancers on a commonly used skin care oil is also discussed, and different timescales of oil penetration into the skin are reported depending on the type of enhancer.

Charge reversal by salt-induced aggregation in aqueous lactoferrin solutions.

We have observed salt-induced aggregation in lactoferrin solutions using dynamic light scattering (DLS). Aggregates start to form once the ionic strength exceeds 10 mM, and are of opposite charge to their monomer building blocks. The presence of aggregates was monitored by electrophoretic measurements, in which the change of isoelectric point in lactoferrin solutions was observed and found to depend on the concentration of background electrolyte. Complimentary atomic force microscopy (AFM) imaging of adsorbed lactoferrin films demonstrated that for negatively charged surfaces (mica, glass) the topography of the adsorbed film remains invariant to changes in ionic strength, whilst for positively charged surfaces (chitosan coated mica) we observed a salt-induced transition in deposited architecture, with approximately 100 nm aggregates being deposited together with monomers for ionic strengths in excess of 10 mM. The size of aggregates observed with AFM is consistent with those observed using DLS. These results suggest that negatively charged lactoferrin aggregates adsorb only onto positively charged surfaces, whereas isolated lactoferrin molecules are sufficiently amphiphilic and adsorb at surfaces of either charge, although without producing a charge inversion effect.

Studying the effectiveness of penetration enhancers to deliver retinol through the stratum cornum by in vivo confocal Raman spectroscopy.

The purpose of this study is to monitor in vivo the effect of chemical penetration enhancers on the delivery of trans-retinol into human skin. Chemical penetration enhancers reversibly alter barrier properties of the SC by disruption of the membrane structures or maximising drug solubility with the skin. So far, most of permeation or penetration experiments are performed in vitro. Raman spectroscopy is uniquely placed to be able to measure biological processes in vivo and this paper shows for the first time that the effect of penetration enhancer on the delivery of trans-retinol can successfully be measured in vivo using this technique. Here, the volar forearm of volunteers was treated with four formulations. One formulation is a highly effective model delivery system identified from ex vivo experiments: trans-retinol in Propylene Glycol (PG)/ethanol, with PG being a well-known and efficient penetration enhancer. The other three formulations are based on 0.3% trans-retinol in Caprylic/Capric Acid Triglyceride (MYRITOL 318), an oil commonly used in skin creams but in two of them a specific penetration enhancer is added. One contains a lipid extractor, Triton X 100, whereas another formulation contains a lipid fluidiser, Oleic Acid. Solutions were applied once and measurements were performed up to 6 h after treatment. Remarkable differences in the delivery of trans-retinol between formulation with or without penetration enhancer can clearly be seen. Moreover, the type of penetration enhancer is also shown to influence the delivery. While using the Oleic Acid, which is a lipid fluidiser, a better delivery of trans-retinol in the skin can be detected. For the first time, the effect of penetration enhancer on the delivery of trans-retinol has been monitored, non invasively in vivo, with time.