No abstract

The relationships between food structure, texture perception and bolus properties during bolus formation are poorly understood. This preliminary single‐subject study on three biscuit recipes investigated the links between bolus macrostructure, perceived texture (using temporal dominance of sensations), and mechanical and rheological properties (using back extrusion and consecutive double compression) throughout mastication. The fracture properties of the biscuits dominated textural perception in the early stages of mastication. As mastication progressed, a sensory transition from dry to sticky was accompanied by an increase in “cohesiveness” and decreases in the consistency coefficient, peak force and “adhesiveness.” At the point of swallow, the boluses were shear thinning pastes and sticky dominated perception. Consistency coefficient and “cohesiveness” indicated different swallowing thresholds for the different recipes. This study found back extrusion to be a suitable method for characterizing biscuit bolus rheology in the later stages of mastication as it is unaffected by bolus dimensions. Practical Applications Mastication of a solid food involves the breakdown of the food and reassembly with saliva into a deformable bolus that can be swallowed safely. The relationships between the perceived texture and structural, mechanical and rheological properties throughout mastication are not well understood. An understanding of these relationships could aid in the design of foods that can be swallowed safely by the elderly or those with dysphagia, or foods that follow a desired oral processing path and thus have a desired texture profile or flavor release.

Siliceous hot spring deposits (sinters) entrap paleoenvironmentally significant components and are used as extreme-environment analogs in the search for early Earth and extraterrestrial life. However, sinters undergo a series of textural and mineralogical changes during diagenesis that can modify and overprint original environmental signals. For ancient hydrothermal settings including those close to the dawn of life, these transformations have long since occurred, so that study of diagenetic processes and effects is best undertaken in much younger deposits still undergoing change. Three young sinters preserve the entire diagenetic sequence of silica phases, from opal-A to quartz. The 6000 to ϳ 11,500 years BP ؎ 70 years sinter at Steamboat Springs, Nevada, the ϳ 1600 -1900 ؎ 160 years BP Opal Mound sinter at Roosevelt Hot Springs, Utah, and the ϳ 456 ؎ 35 years BP deposit at Sinter Island, Taupo Volcanic Zone, New Zealand, provide an opportunity to track crystallographic, mineralogic and morphologic transitions of sinter diagenesis using standard and new analytical approaches. Worldwide, sinter forms from cooling, alkali chloride waters as noncrystalline opal-A, transforming first into noncrystalline opal-A/CT, then paracrystalline opal-CT ؎ moganite, paracrystalline opal-C, and eventually to microcrystalline quartz. In this study, these changes were identified by the novel and combined application of electron backscatter diffraction, X-ray powder diffraction, and scanning electron and optical microscopy techniques. We show that mineralogical changes precede morphological and accompanied crystallographic transformations. During this modification, silica particles grow and shrink several times from the micron-to nano-meter scales via dissolution, reprecipitation and recrystallization, and diagenesis follows the Ostwald Step rule. All deposits followed nearly identical diagenetic pathways, with time as the only variable in the march toward physicochemically stable quartz crystals. Diagenesis alters original environmental signatures trapped within sinters. After five silica phase changes, filamentous microfossils are modified but still remain recognizable within sinter from the Opal Mound and Steamboat Springs deposits, and during the opal-A to opal-CT silica phase transformations at Sinter Island. Therefore, delineating diagenetic components and how they affect sinters is necessary to accurately identify biosignals from ancient hot-spring deposits.

No abstract

The structure of chocolate is drastically transformed during oral processing from a composite solid to an oil/water fluid emulsion. Using two commercial dark chocolates varying in cocoa solids content, this study develops a method to identify the factors that govern lubrication in molten chocolate and saliva's contribution to lubrication following oral processing. In addition to chocolate and its individual components, simulated boluses (molten chocolate and phosphate buffered saline), in vitro boluses (molten chocolate and whole human saliva) and ex vivo boluses (chocolate expectorated after chewing till the point of swallow) were tested. The results reveal that the lubrication of molten chocolate is strongly influenced by the presence of solid sugar particles and cocoa solids. The entrainment of particles into the contact zone between the interacting surfaces reduces friction such that the maximum friction coefficient measured for chocolate boluses is much lower than those for single-phase Newtonian fluids. The addition of whole human saliva or a substitute aqueous phase (PBS) to molten chocolate dissolves sugar and decreases the viscosity of molten chocolate so that thinner films are achieved. However, saliva is more lubricating than PBS, which results in lower friction coefficients for chocolate-saliva mixtures when compared to chocolate-PBS mixtures. A comparison of ex vivo and in vitro boluses also suggests that the quantity of saliva added and uniformity of mixing during oral processing affect bolus structure, which leads to differences in measured friction. It is hypothesized that inhomogeneous mixing in the mouth introduces large air bubbles and regions of non-emulsified fat into the ex vivo boluses, which enhance wetting and lubrication.