Thermoresponsive colloidal microgels and polymeric solutions at rest and under shear

The structure of temperature-sensitive poly(N-isopropylacrylamide) (PNiPAM) microgels was investigated by means of small-angle neutron scattering (SANS). A direct modeling expression for the scattering intensity was derived. The influences of temperature, cross-linking density and particle size on the structure were revealed by the radial density profiles and clearly showed that the segment density in the swollen state was not homogeneous but gradually decayed at the surface. The density profile revealed a box profile only when the particles were collapsed at elevated temperatures. The overall particle size and the correlation length of the concentration fluctuations of the internal polymer network decreased with concentration revealing the increasing compression of the spheres. The interaction potential did not change significantly between 25°C and 32°C. Microgels with different degrees of cross-linking and particle size resembled true hard sphere behavior up to effective volume fractions of <0.35. At higher effective volume fractions strong deviations from true hard spheres were observed. At temperatures well above the LCST the interaction potential became strongly attractive. The collapsed microgel spheres formed aggregates consisting of flocculated particles without significant long-range order. Rheo-SANS experiments revealed that the shear-induced particle arrangements strongly depend on the interaction potential. When the interaction potential was repulsive at temperatures below the LCST, no significant deformation of the swollen PNiPAM particles was observed. Shear-induced ordering was found resulting in the formation of two dimensional hexagonal close packed layers that aligned along the flow direction giving rise to shear thinning. At temperatures near the LCST, when the particle interaction potential is not yet strongly attractive, shear flow induced the collapse of an individual particle. A so-called butterfly scattering pattern indicated the shear-induced enhancement of concentration fluctuations along the flow direction leading to solvent being squeezed out of the particles. The influence of shear flow on the phase separation of PNiPAM microgels was investigated by means of rheo-turbidity and rheo-SANS and compared to the behavior of linear PNiPAM macromolecules. The rheological behavior of concentrated microgel suspensions depended strongly on temperature, but flow and viscoelastic properties of concentrated solutions of the linear polymer were not significantly affected by temperature changes. Shear induced phase separation was observed for both polymer architectures, although the viscoelastic properties of the two systems have different structural origins. For solutions of aqueous linear chain PNiPAM in the semi-dilute regime at different shear rates the existence of a threshold shear stress was observed and the phase separation process became faster with increasing stress. The two dimensional scattering patterns remained isotropic even during the phase separation process and the correlation length increased. The influence of shear flow on the phase separation process has apparently an analogous effect as a temperature increase

Characterisation of friction behaviour of intact soft solid foods and food boli

Methodologies to quantify friction forces between soft solid foods or food boli and (model) oral surfaces are desired to better understand how changes in food properties during oral processing affect sensory perception. In this short communication, friction forces (FF) occurring between polydimethylsiloxane (PDMS) surfaces and intact soft solid foods/boli were quantified. As models for intact foods, we used gelatine gels varying in composition and particle size, and sausages were used as an example for real foods. Friction forces measured during the relative motion of intact foods against a rough PDMS surface (“oral surface”), strongly depended on the composition of the food. Friction forces were significantly lower for PDMS against emulsion-filled gels, than for PDMS against unfilled gels, likely due to the lubricating effect of released oil from the gel. Moreover, sausages, displayed significantly higher friction forces than gelatine gels when moving against the PDMS probe, presumably linked to differences in the surface of the foods. The friction forces observed for the PDMS probe moving against food boli were dependent on particle size and saliva quantity; boli with larger particle sizes showed significantly lower friction forces, whereas the addition of saliva to food boli first increased friction forces, but with increasing amount decreased the friction forces significantly. We conclude that the presented methodology is able to quantify the friction behaviour of intact soft solid foods and boli directly, taking into account (i) the effect of composition and added fillers, (ii) serum or oil release and (iii) bolus particle size.</p

Differences in habitual eating speed lead to small differences in dynamic sensory perception of composite foods

Previous studies demonstrated that variability in oral processing behaviors impacts bolus properties and consequently texture and flavor perception. However, most studies followed a prescribed mastication protocol during the products' sensory evaluations. A better understanding of how variability in habitual eating behavior impacts sensory perception of foods is needed. The aim of this study was to investigate the effect of habitual eating speed (slow vs. fast eaters) on dynamic sensory perception of composite foods. Habitual oral processing behavior of different composite foods was quantified in 105 participants. Participants were divided in fast (n&nbsp;=&nbsp;53) and slow (n&nbsp;=&nbsp;52) eaters using a median split. Three formulations of strawberry jams varying in viscosity and sugar content (High Sugar/Low Pectin [Control], High Sugar/High Pectin, Low Sugar/Low Pectin) were used. Composite foods were prepared by spreading jams on breads. Dynamics of dominant sensory attributes of strawberry jams presented with and without breads were evaluated using Temporal Dominance of Sensations (TDS). Dynamic sensory perception of jams and jam-bread combinations differed only slightly for short periods of time between habitual slow and fast eaters. The addition of breads to jams reduced especially the ability of the fast eaters to discriminate between jams differing in formulation. Slow eaters discriminated between different formulations of jams better than fast eaters, regardless of whether jams were presented alone or in combination with breads. We conclude that differences in habitual eating speed between consumers lead to small differences in dynamic sensory perception and discrimination ability of composite food

Does the face show what the mind tells? A comparison between dynamic emotions obtained from facial expressions and Temporal Dominance of Emotions (TDE)

Measuring food-evoked emotions dynamically during consumption can be done using explicit self-report methods such as Temporal Dominance of Emotions (TDE), and implicit methods such as recording facial expressions. It is not known whether or how dynamic explicit and implicit emotion measures correspond. This study investigated how explicit self-reported food-evoked emotions evaluated with TDE are related to implicit food-evoked emotions determined from facial expressions. Fifty-six participants evaluated six yogurts with granola pieces varying in size, hardness and concentration, using multiple bite assessment employing TDE for the first, third and fifth bite of consumption. Consumers were video recorded during each bite of consumption and facial expressions were analysed using FaceReader™. Happy, interested, disgusted and bored were similar descriptors measured explicitly and implicitly. Little overlap was observed regarding the type of emotion characterization by FaceReader™ and TDE. Products were mainly discriminated along the valence dimension (positive – negative), and directly reflected product discrimination in terms of liking. FaceReader™ further differentiated the least liked products from each other on arousal and negative facial expressions. Our results indicated little dynamics in food-evoked emotions within and between bites. Facial expressions seemed more dynamic within bites, while explicit food-evoked emotion responses seemed more dynamic between bites. We conclude that FaceReader™ intensities of emotions and dominance durations observed in TDE are not directly comparable and show little overlap. Moreover, food-evoked emotion responses were fairly stable from first to last bite and only very limited changes were observed using implicit and explicit emotions measures.</p

The Major Ciliary Isoforms of RPGR Build Different Interaction Complexes with INPP5E and RPGRIP1L

X-linked retinitis pigmentosa (XLRP) is frequently caused by mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. A complex splicing process acts on the RPGR gene resulting in three major isoforms: RPGR(ex1-19), RPGR(ORF15) and RPGR(skip14/15). We characterized the widely expressed, alternatively spliced transcript RPGR(skip14/15) lacking exons 14 and 15. Using the CRISPR/eSpCas9 system, we generated HEK293T cell lines exclusively expressing the RPGR(skip14/15) transcript from the endogenous RPGR gene. RPGR(ex1-19) and RPGR(ORF15) were knocked out. Immunocytochemistry demonstrated that the RPGR(skip14/15) protein localizes along primary cilia, resembling the expression pattern of RPGR(ex1-19). The number of cilia-carrying cells was not affected by the absence of the RPGR(ex1-19) and RPGR(ORF15) isoforms. Co-immunoprecipitation assays demonstrated that both RPGR(ex1-19) and RPGR(skip14/15) interact with PDE6D, further supporting that RPGR(skip14/15) is associated with the protein networks along the primary cilium. Interestingly, interaction complexes with INPP5E or RPGRIP1L were only detectable with isoform RPGR(ex1-19), but not with RPGR(skip14/15), demonstrating distinct functional properties of the major RPGR isoforms in spite of their similar subcellular localization. Our findings lead to the conclusion that protein binding sites within RPGR are mediated through alternative splicing. A tissue-specific expression ratio between RPGR(skip14/15) and RPGR(ex1-19) seems required to regulate the ciliary concentration of RPGR interaction partners

In vivo aroma release and dynamic sensory perception of composite foods

8openInternationalInternational coauthor/editorCondiments such as spreads, dressings, or sauces are usually consumed together with carrier foods such as breads or vegetables. Dynamic interactions between condiments and carriers occur during consumption, which can influence aroma release and perception. This study investigated in vivo aroma release (PTR-MS) and dynamic sensory perception (time–intensity) of mayonnaises spiked with lemon aroma (limonene, citral). Mayonnaises were assessed without and with carrier foods (bread, potato). When different mayonnaises were consumed and assessed alone, aroma release and intensity perception were positively correlated. Interestingly, when mayonnaises were combined with carriers, aroma release and perception were no longer positively correlated. Addition of carriers increased release of limonene and citral into the nasal cavity during consumption but decreased perceived aroma intensity of condiments. The increase in aroma release induced by the carriers can be explained by differences in oral processing behaviors and by the increased surface area of mayonnaise-carrier combinations. Carrier addition is likely to modulate aroma perception of composite foods by cross-modal texture–aroma interactions. This work demonstrates that not only physicochemical characteristics of foods but also cross-modal interactions play a role in influencing flavor perception of composite foods.openvan Eck, Arianne; Pedrotti, Michele; Brouwer, Rutger; Supapong, Arpavee; Fogliano, Vincenzo; Scholten, Elke; Biasioli, Franco; Stieger, Markusvan Eck, A.; Pedrotti, M.; Brouwer, R.; Supapong, A.; Fogliano, V.; Scholten, E.; Biasioli, F.; Stieger, M

Spray-dried microfibrillated cellulose particles as texture modifier in liquid foods and their effect on rheological, tribological and sensory properties

Microfibrillated cellulose (MFC) has potentisal to be used as clean label texture modifier in foods due to its structural and mechanical properties. These properties deteriorate upon drying of MFC dispersions due to aggregation of the microfibrils. In this study dried MFC particles were prepared by spray-drying MFC dispersions in a surplus of maltodextrin to prevent hornification. The aim of this study was to evaluate the effect of MFC particle concentration and MFC:maltodextrin ratio of dried MFC powders on rheological, tribological and sensory texture properties of liquid foods. Scanning Electron Microscopy demonstrated that after spray-drying, MFC powders with polydisperse particle size distribution were obtained (1–30 μm). Upon suspension of spray-dried MFC powder in water, maltodextrin dissolved in the aqueous continuous phase whereas spherical MFC networks retained their shape and co-existed in a mixture with individual fibrils. Spray-dried MFC powders were added to skimmed milk and tomato soup at different concentrations. With increasing concentration of dried MFC particles, shear viscosity, consistency index K, storage and loss modulus of skimmed milks and tomato soups increased whereas flow index n decreased. Addition of spray-dried MFC particles to milks and soups significantly (p < 0.05) increased sensory thickness and creaminess. Milks displayed similar tribological properties irrespective of MFC particle concentration, which was presumably caused by exclusion of the MFC network from the tribological gap. Rheological properties, thickness and creaminess increased more effectively upon addition of low MFC:maltodextrin particles compared to particles with high MFC:maltodextrin ratio. We conclude that spray-dried microfibrillated cellulose particles can be used as thickener or fat replacer in liquid foods

Effect of Taste Enhancement on Consumer Acceptance of Pureed Cucumber and Green Capsicum

Abstract: Vegetables have low taste intensities, which might contribute to low acceptance. The aim of this study was to investigate the effect of taste (sweetness, sourness, bitterness, umami, and saltiness) and fattiness enhancement on consumer acceptance of cucumber and green capsicum purees. Three concentrations of sugar, citric acid, caffeine, mono-sodium glutamate, NaCl, and sunflower oil were added to pureed cucumber and green capsicum. Subjects (n = 66, 35.6 ± 17.7 y) rated taste and fattiness intensity. Different subjects (n = 100, 33.2 ± 16.5 years) evaluated acceptance of all pureed vegetables. Taste intensities of vegetable purees were significantly different (P < 0.05) between the three tastant concentrations except for umami in both vegetable purees, sourness in green capsicum puree, and fattiness in cucumber puree. Only enhancement of sweetness significantly (P < 0.05) increased acceptance of both vegetable purees compared to unmodified purees. In cucumber purees, relatively small amounts of added sucrose (2%) increased acceptance already significantly, whereas in green capsicum acceptance increased significantly only with addition of 5% sucrose. Enhancement of other taste modalities did not significantly increase acceptance of both vegetable purees. Enhancing saltiness and bitterness significantly decreased acceptance of both vegetable purees. We conclude that the effect of taste enhancement on acceptance of vegetable purees differs between tastants and depends on tastant concentration and vegetable type. With the exception of sweetness, taste enhancement of taste modalities such as sourness, bitterness, umami, and saltiness was insufficient to increase acceptance of vegetable purees. We suggest that more complex taste, flavor, or texture modifications are required to enhance acceptance of vegetables. Practical Application: Results can be used by cultivators to select and grow vegetable varieties with enhanced taste and flavor. Especially for cucumber, relatively small sweetness enhancement is sufficient to increase acceptance.</p

Oral processing behavior and dynamic sensory perception of composite foods : Toppings assist saliva in bolus formation

Composite foods consist of combinations of single foods, such as bread with toppings. Single foods can differ considerably in their mechanical and sensory properties. This study aimed to investigate the effect of toppings on oral processing behavior and dynamic sensory perception of carrier foods when consumed as composite foods. Two carriers (bread, crackers) and three toppings (firm cheese, cheese spread, mayonnaise) were selected and six carrier-topping combinations were prepared. Mastication behavior, bolus properties (33, 66 and 100% of total mastication time) and dynamic sensory perception were determined for single carriers and all carrier-topping combinations. Both carriers with cheese spread and mayonnaise were chewed shorter and with fewer chews than single bread and crackers, although twice the mass of food was consumed. These toppings contributed to a faster bolus formation by providing moisture, so that less saliva was incorporated into the bolus during mastication. As a result of the moisture incorporation, carrier boli with toppings were softened and perceived less firm and less dry than carrier boli alone. The largest effects of toppings on oral processing behavior and perception were found for liquid-like mayonnaise, and these effects were more pronounced in dry crackers than in moist bread. We conclude that toppings assist saliva in bolus formation of carriers. Carriers drive oral processing behavior and texture perception whereas toppings drive overall flavor perception. This knowledge contributes to food design tailored for specific consumer segments and future personalized nutrition.</p