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Rice pellets were produced by extrusion according to an experimental design varying temperature (120–135–150 °C), moisture content (17–20–23%) and screw speed (300–400–500 rpm). The internal expanded structure of the pellets was assessed by X-ray tomography and texture with a texture analyser. The extent of starch depolymerisation and the types of protein depolymerisation/interactions were studied in complement to the starch–proteins morphology assessed by microscopy. The physico-chemical properties of the pellets were mainly affected by moisture and temperature, with moisture having the highest impact. High moisture content (23%) resulted in higher mean walls thickness of the extruded pellet, less starch depolymerisation, more protein aggregation through disulfide bonds and harder pellets. The internal expanded structure and texture of the rice pellets were mainly explained by protein changes and less by the extent of starch depolymerisation in this study. When proteins mainly interacted through medium energy interactions (disulfide bonds), protein aggregates were larger, cells walls thicker and pellets were less porous and harder with more fracture events. On the contrary, when proteins interacted through low energy (hydrogen and hydrophobic bonds) and high energy bonds (unextractable proteins), proteins were more depolymerised and aggregates were smaller and finely distributed, cells walls thinner and pellets were less hard with less fracture events.

Structure and texture of extruded cereals were investigated on products obtained from different flours (whole wheat flour and corn flour recipes) and for different fibre addition levels. Texture, i.e. mechanical properties, was assessed through a compression test and structure was analysed via microcomputed X-ray tomography and 3D image analysis. The addition of fibres at different levels in wheat and corn recipes strongly decreased porosity, thus leading to harder products. The acoustic properties, obtained from a contact method assumed to simulate biting and bone conduction of the sound, are also modified by the amount of added fibres. The acoustic properties can be related to product structure and mechanical properties. Industrial relevance • This study was performed within the European InsideFood project and extruded cereals were produced in an industrial environment. • The main objective was to find the drivers of texture changes in extruded cereals when fibres were added in the recipe. • Texture measurements, i.e. mechanical properties of cereals assessed by compression tests are commonly used as physical measurements. • Even though acoustic emission has largely been used before in previous studies, the method used here differs as it is a contact method. • The uniqueness of this study was to combine structural information with physical results (hardness and acoustic emission), and to find out the main structure attributes that drive these physical attributes. • Understanding the impact of structure on texture is key, since it helps in designing the right structure through the right processing conditions to target the desired texture properties. • This study showed that cellular structure is key – however, another level that has also to be addressed is the wall structure – at the moment, we are still lacking convenient and quick methods to assess dispersion of protein, and fibres in the starch matrix (microscopy is time-consuming). It is known that it plays a role in the breaking behaviour of cereal products. We have seen here in our study that acoustic emission can be linked to the number of peak upon compression. This may reflect the structural organisation at the walls level.

Extruded cereals mainly composed of starch and enriched in fibers were produced with two types of base recipes: (i) one recipe mainly composed of wheat flour and (ii) one recipe mainly composed of corn and soya flours. The addition of fibers was performed through the use of oat bran concentrate or wheat bran, up to 32% of the recipe. The structure of the extrudates, assessed by X-ray tomography, pointed out the decrease of porosity and of mean cells size with the increase of the total dietary fibers content of the recipe. The hardness of the products, i.e. the maximum stress determined by a compression test, was linked to their porosity. The Gibson-Ashby relationship could be applied and the fit was even improved when considering the walls of the solid foam as composite materials. Fibers and proteins can be indeed considered as particles dispersed in the starchy phase. This work thus shows the impact of the structure of the extrudates on their mechanical properties. The structure is taken into account at different length scales; at the level of the porous structure and at the level of the phase of the main biopolymers present in the recipe (starch, proteins and fibers). The mechanical behavior of these products is then discussed according to their characteristics of composite solid foams.

The effect of excess excitation energy on the rotational dynamics of rhodamine 6G in the ground and the first singlet excited state has been investigated in series of n-alcohols and alkanenitriles using the picosecond polarization grating technique. In nitriles, the reorientation times are the same for excitation at the S1 ← S0 and S2 ← S0 transitions, and no state dependence could be detected. In alcohols, the rotational dynamics of rhodamine 6G in the excited state is about 25% faster when formed with 1.15 eV excess excitation energy. This effect is ascribed to a decrease of the hydrodynamic volume due to dissociation of solute/solvent hydrogen bond following intramolecular vibrational redistribution. An accompanying perturbation of the solvent shell structure caused by the fast local temperature jump is not excluded.

BACKGROUND: Beverage powders can exhibit caking during storage due to high temperature and moisture conditions, leading to consumer dissatisfaction. Caking problems can be aggravated by the presence of sensitive ingredients. The caking behaviour of cocoa beverage powders, with varying amounts of a carbohydrate sensitive ingredient, as affected by climate conditions was studied in this work. Sorption isotherms of beverage powders were determined at water activities (aw) ranging from 0.1 to 0.6 in a moisture sorption analyser by gravimetry and fitted to the Brunauer–Emmett–Teller (BET) or the Guggenheim–Anderson–de Boer (GAB) equation. Glass transition temperatures (Tg) at several aw were analysed by differential scanning calorimetry and fitted to the Gordon–Taylor equation. Deduced Tg = f(aw) functions helped to identify stability or caking zones. Specific experimental methods, based on the analysis of mechanical properties of powder cakes formed under compression, were used to quantify the degree of caking. Pantry tests complemented this study to put in evidence the visual perception of powder caking with increasing aw. RESULTS: The glass transition approach was useful to predict the risks of caking but was limited to products where Tg can be measured. On the other hand, quantification of the caking degree by analysis of mechanical properties allowed estimation of the extent of degradation for each product. CONCLUSION: This work demonstrated that increasing amounts of a carbohydrate sensitive ingredient in cocoa beverages negatively affected their storage stability. Copyright © 2011 Society of Chemical Industry

Incorporation of fiber in cereals may lead to quality issues, thus decreasing consumer acceptance. This is partially due to deterioration of the microstructure, one of the primary quality attributes of cereals. The objective of this study was to better understand the mechanisms by which dietary fibers affect the quality of cereal products during extrusion-cooking. The study quantified the effect of amount and type of fiber and whole grain on (i) texture, (ii) structure, and (iii) rehydration properties of extruded cereals. New innovative methods were applied and combined with traditional techniques to characterize both the structure and the rehydration properties. Extruded cereals were produced using a starch-based recipe (whole and wheat flours) and two sources of fibers (oat bran concentrate and wheat bran). The oat and wheat bran levels used in this study were 0, 10, and 20%. The different mixtures were extruded in a pilot twin-screw extruder BC21 (Clextral) and then sugar coated after drying. Mechanical properties of extruded cereals were investigated by compression test. The cellular structure was observed by X-ray tomography. The quality of coating (thickness, homogeneity) was analyzed by optical coherence tomography. The rehydration properties of such cereals in milk were evaluated by magnetic resonance imaging and optical coherence tomography. This work revealed that structure assessment of extruded cereals may lead to a better understanding of the effect of fiber addition on texture and rehydration properties. The application of innovative methods, such as optical coherence tomography and magnetic resonance imaging, was found to be useful to quantify the structural properties.

Foamed beverages, such as cappuccino, have become very popular with consumers in recent years. Though the main appeal of such products lies in their milky frothy top, there is a lack of understanding on the liquid properties and process parameters driving froth quality. There are also no reliable methods to evaluate foam characteristics, since most studies to date focus on avoiding milk foaming during packaging and heat treatment, or on the behaviour of pure protein foams. The present study aims to understand the mechanisms of foam formation in milk, with a view to producing a froth that is more appealing to consumers. A methodology to characterize and distinguish between milk foams generated by two main methods—mechanical agitation and steam injection—is presented. The methodology involves characterizing the foam in terms of initial bubble hold-up, foam destabilization mechanisms and kinetics. Observation on foams formed by steam injection revealed that steam injection time does not have a significant effect on initial bubble hold-up even though it increases general foam stability. The increase on foam stability is most probably related to the greater extent of protein denaturation induced by increasing steam injection time. In the case of mechanically whipped milk foams, it was observed that higher milk temperatures resulted in dispersions having a lower bubble hold-up. The overall stability of the higher temperature foam expressed in terms of foam-to-liquid ratio was also lower as initial milk temperature increased. Higher milk temperatures induced by increasing steam injection time didn't affect foam stability, whereas whipping at higher temperatures had a strong destabilizing effect. This suggests that mechanisms of interface formation by the two methods differ and reinforces that an understanding of the changes occurring in milk during aeration by steam injection is essential to establish the differences between foams generated by both processes.

The electron transfer (ET) quenching dynamics of excited perylene (Pe), cyanoperylene (PeCN), methanolperylene (PeOH), and methylperylene (PeMe) in N,N-dimethylaniline (DMA) has been investigated using ultrafast fluorescence up-conversion. Measurements of the rotational dynamics of PeCN and PeMe in nonpolar and polar inert solvents using optically heterodyned polarization spectroscopy are also presented. The fluorescence decay in DMA is strongly nonexponential and about 10 times faster with PeCN than with the other electron acceptors. The quenching dynamics has been analyzed with a model distinguishing three types of donor molecules surrounding the acceptor: those with optimal orientation for ET and those requiring orientational or translational diffusion prior to ET. According to this model, which can account for the whole fluorescence decay, the faster quenching dynamics of PeCN is not due to a larger ET rate constant, but to a larger number of donor molecules, typically three to four, with an optimal orientation. This is explained by the effect of dipole−dipole interaction between PeCN and the donor molecules, which favors mutual orientations with a large electronic coupling. With the other acceptors, this interaction is either not present or does not lead to ET active geometries. The occurrence of this interaction is substantiated by the rotational dynamics measurements.

The excited-state dynamics of the radical cations of perylene (PE•+), tetracene (TE•+), and thianthrene (TH•+), as well as the radical anions of anthraquinone (AQ•-) and tetracenequinone (TQ•-), formed by γ irradiation in low-temperature matrices (PE•+, TH•+, AQ•-, and TQ•-) or by oxidation in sulfuric acid (PE•+, TE•+, and TH•+) have been investigated using ultrafast pump−probe spectroscopy. The longest ground-state recovery time measured was 100 ps. The excited-state lifetime of PE•+ is substantially longer in low-temperature matrices than in H2SO4, where the effects of perdeuteration and of temperature on the ground-state recovery dynamics indicate that internal conversion is not the major decay channel of PE•+*. The data suggest that both PE•+* and TE•+* decay mainly through an intermolecular quenching process, most probably a reversible charge transfer reaction. Contrarily to AQ•-*, TQ•-* exhibits an emission in the visible which, according to theoretical calculations, occurs from an upper excited state.

The solvation dynamics of an organic dye, IR140, in methanol, ethanol, and in a series of six alkanenitriles has been investigated using the transient grating technique. In all solvents, the dynamics exhibit ultrafast, almost solvent-independent, components ascribed to inertial solvation, and a slower viscosity-dependent component, due to diffusive solvation. The relative amplitudes of these components depend on both the solvent and on the wavelength at which the experiment is performed. The contribution of inertial motion increases with decreasing size of the solvent molecules and with decreasing wavelength. It appears that diffusive motion is associated with a loose solvent shell, while inertial motion dominates when the solvation layer is dense.

A study of the dynamics of ground-state recovery of the perylene radical cation (Pe•+), of perylene radical anion (Pe•-), and of anthraquinone radical anion (AQ•-) is reported. In boric acid glass, the excited-state lifetime of Pe•+ is 35 ± 3 ps, while in concentrated sulfuric acid, it is smaller than 15 ps, the time resolution of the experimental setup. The excited-state lifetime of Pe•+, Pe•-, and AQ•- generated by photoinduced intermolecular electron-transfer reaction in MeCN is shorter than 15 ps. In the case of Pe•-, the uncomplete ground-state recovery is ascribed to the occurrence of electron photoejection. The free ion yield in the intermolecular electron-transfer reaction between 9,10-dicyanoanthracene (DCA) and two electron acceptors was measured in a two-pulse experiment, where the second pulse excited the ensuing DCA•-. This excitation has no influence on the magnitude of the free ion yield, indicating a short excited-state lifetime of DCA•-* relative to the time scale of back electron transfer and ionic dissociation. A red emission, ascribed to the fluorescence of protonated Pe, was detected in boric acid glass and sulfuric acid. No fluorescence that could be clearly ascribed to Pe•+* could be observed.