A comparison of the sensory and rheological properties of molecular and particulate forms of xanthan gum.

A particulate form of xanthan gum was prepared by extrusion cooking. The temperature dependence of the viscosity of this form shows similarities to starch with an increase in viscosity to a maximum with increasing temperature as a result of the swelling of the particles. The rheology and mixing behaviour with water of the particulate and conventional molecular forms of xanthan were compared with a modified starch. The particulate xanthan products mixed rapidly with water in a similar way to ungelatinised starch, whereas conventional molecular xanthan systems mixed poorly. Using an experienced sensory panel, model tomato products thickened with the three systems were compared at equal shear viscosities. The panel could not discriminate between the tomato flavour of the three products, but found that the xanthan products were perceived as being significantly thicker. These observations were consistent with previous work. Salt perception for both xanthan products was poorer than for the starch thickened systems. A hypothesis to explain why xanthan does not fit into the previously postulated link between mixing and perception is presented.

Shear rheology and filament stretching behaviour of xanthan gum and carboxymethyl cellulose solution in presence of saliva.

The objective of the work reported in this paper is to determine if saliva addition has an effect on the rheology of xanthan gum solutions. The reasons for the interest was that it has been previously reported that flavour release from high viscosity xanthan thickened foods is not reduced in the same way as foods thickened by other hydrocolloids at comparable viscosities. It was previously postulated that this could be due to an interaction between saliva and xanthan that could change the microstructure and rheology of xanthan solutions. In this work the effect of saliva on the rheology of CMC and xanthan solutions was compared. Solutions of molecularly dissolved xanthan gum and CMC mixed with water or human whole saliva at a ratio of 5:1 showed little impact of the presence of saliva on steady shear or dynamic viscosity for the two hydrocolloids. In filament thinning experiments saliva addition significantly increased filament break-up time for xanthan gum while it had little effect on the break-up time of the CMC filament. Also, filament thinning appeared a lot less even and was not as reproducible in the case of xanthan gum. Addition of CMC and hydroxypropyl methylcellulose (HPMC) to xanthan gum solutions showed a similar increase in break-up time to saliva, but to see this effect the viscosity of the added CMC or HPMC solution had to be very much higher than the viscosity of saliva. The results are discussed in the context of the structure of xanthan gum and the reported extensional rheology of saliva.

Solvent effects on starch dissolution and gelatinization.

The disruption of starch granular structure during dissolution in varying concentrations of N-methyl morpholine N-oxide (NMMO) has been studied using three maize starches with varying ratios of amylose and amylopectin. Behavior in NMMO has been characterized by differential scanning calorimetry (DSC), microscopy, rapid viscosity analysis (RVA), and rheometry. Exothermic transitions were observed for the three starches in both 78 and 70% NMMO; the transition changed to an endotherm at 60 and 50% NMMO. Consistent with DSC, hot stage microscopy showed that starch granules dissolved at NMMO concentrations of 78 and 70%, whereas in 60 and 50% NMMO, gelatinization behavior similar to that found for starch in water was observed. Mechanical spectroscopy revealed the dominant viscous behavior (G″ > G') of starch at NMMO concentrations of 70 and 78% and more elastic behavior (G' > G″) at lower concentrations. Starch solutions in 78% NMMO obey the Cox-Merz rule, suggesting that the solutions are homogeneous on a molecular level.

Comparison of the mechanical properties of cellulose and starch films.

Some effects of water at levels up to 25% (dry solids basis db) on regenerated cellulose films with a thickness of 100 mum were investigated by dynamic vapor sorption (DVS), X-ray diffraction, tensile testing, and proton-nuclear magnetic resonance (NMR). The sorption isotherm fitted by the D'Arcy and Watt model and the increase in NMR T(2) with water content suggest that a mobile water fraction appears at water contents above 10%db. Water absorption increased the crystallinity of cellulose films from 31% (dry) to 38% (25%db) and altered the dimensions of crystallites. Mechanical measurements on planar and notched samples at all the water contents used here showed ductile fracture behavior. Although the properties of water in these cellulose films are comparable to previously reported data on starch, cellulose films at low water content are much less brittle than starch. The reasons for this difference are explored.

Impact of the extrusion process on xanthan gum behaviour.

Processing xanthan gum by extrusion and subsequent drying produces a biopolymer showing particulate, rather than molecular behaviour in aqueous solution. This form of xanthan disperses very readily to give a viscosity that is strongly dependent on salt concentration. On heating above the temperature of the order-disorder transition as determined by calorimetry, there is a viscosity transition that is indicative of the irreversible loss of the particulate structure. It is suggested that the extrusion process melts and aligns xanthan macromolecules. On cooling reordering will occur but in the highly concentrated environment in the extruder ( approximately 45% water w/w), inter-molecular association between neighbouring macromolecules cannot proceed to completion due to kinetic trapping. As a consequence a network structure is created maintained by associations involving ordered regions. A xanthan solution can be prepared from this particulate material by dispersing and subsequent heating far more readily than can be achieved with non-processed xanthan.

Sorption behavior of mixtures of glycerol and starch.

Glycerol is often added to starches to plasticize the product, but the presence of glycerol may also affect the water content of the samples. To evaluate the effect of glycerol on the sorption properties of starches, waxy maize, rice, and wheat starch were thermomechanically extruded in the presence of glycerol. Sorption isotherms of these extruded samples were ascertained using dynamic vapor sorption (DVS). BET and GAB modeling showed a monolayer (mo) significantly higher for waxy maize than for rice and wheat. Glycerol inclusion changed the model values, indicating reduction in sorption energy at the monolayer and restructuring of the multilayer. An interaction factor (xi) based on weight fraction models was calculated. Differences in xi were obtained when glycerol was added, varying from approximately 0.9 for 5% glycerol to approximately 0.8 for 20% glycerol, supporting the hypothesis of interactions between starch and this polyol.

In-mouth amylase activity can reduce perception of saltiness in starch-thickened foods.

Sensory scores for saltiness and thickness obtained for savory liquids thickened with starches or the nonstarch hydrocolloid hydroxypropylmethyl cellulose (HPMC) were correlated with the panelists' amylase activity. Although higher enzyme activities were linked to lower thickness scores for systems thickened by starch, they were also associated with a decreased taste perception, particularly for starches retaining a granular structure after gelatinization (wheat and modified waxy maize). Microscopic evidence showed that the enzyme can disrupt such structures, and this is associated with a decreased mixing efficiency with water and consequently a reduced transport of tastant (sodium) to the saliva (aqueous) phase and to the taste buds. This explains the lower saltiness scores for subjects with higher amylase activity, even if they are associated with a lower perceived thickness.

A review of mental health recovery programs in selected industrialized countries.

The concept of recovery has gained increasing attention and many mental health systems have taken steps to move towards more recovery oriented practice and service structures. This article represents a description of current recovery-oriented programs in participating countries including recovery measurement tools. Although there is growing acceptance that recovery needs to be one of the key domains of quality in mental health care, the implementation and delivery of recovery oriented services and corresponding evaluation strategies as an integral part of mental health care have been lacking.

Testing the validity of comparisons between the rheological and the calorimetric glass transition temperatures.

Dynamic mechanical techniques are used increasingly in the investigation of vitrification phenomena in biological materials, thus posing the question of whether the rheological T(g) should be compared with the established practice of obtaining T(g) values from differential scanning calorimetry. The nature of the rheological T(g) is discussed and its frequency dependence is established with a view to facilitating comparisons with calorimetric data. Despite claims made in the literature, results on high sugar-kappa-carrageenan mixtures, hydrated gelatin films, and thermoset epoxy resins demonstrate that there is no clear reference point for comparison of the glass transition temperatures derived with the two techniques. Furthermore, the structure-forming ability of kappa-carrageenan and other biopolymers impacts primarily upon the mechanical manifestation of vitrification and contributes to the state of complexity of comparisons between thermal and mechanical data.

High sugar/polysaccharide glasses: resolving the role of water molecules in structure formation.

Small-deformation dynamic oscillation and differential scanning calorimetry were used to ascertain the role of water molecules in high sugar/polysaccharide glasses. Increasing replacement of water with sugar affects adversely tahe degree of order in the polysaccharide network to such an extent that at level of solids >90% structure formation is no longer possible. Depending of the polymeric ability to form a network, the rheological T(g) can be up to 30 degrees higher than the calorimetric T(g).

Evaluation of multiple transfer of DNA using mock case scenarios.

DNA transfer and its possible role in explaining the presence of a biological sample at a crime scene is becoming more prevalent in criminal investigations and related court proceedings. To assist understanding of DNA transfer and assess the extent to which we can utilise already available information regarding transfer of DNA we compare transfer rates determined from mock multi-step transfer scenarios with transfer rates predicted by the application of currently available transfer rate data. The transfer results obtained from the scenarios tested were, in some instances, different (both lower and higher rates) from those predicted. These discrepancies are most likely the result of the impact of as yet untested variables. These may include the variations in substrate type, transfer area size and environmental factors such as temperature and humidity among others. Whilst detailed re-enactments of proposed transfer scenarios, that take into account the many possibly relevant aspects affecting transfer are desirable, to provide an accurate likelihood estimate, these are not always possible. The application of detailed transfer rate tables that include data on the many factors affecting transfer could provide a useful substitute for evaluating the likelihood of specific transfer events. The value and accuracy derived from applying such tables will improve as more research in this area is conducted and the tables expanded and refined.

DNA transfer within forensic exhibit packaging: potential for DNA loss and relocation.

Crime scene samples after their collection are packaged and transported to the laboratory for examination and DNA analysis. The amount and location of DNA-containing material retrieved from an exhibit can be critical in acquiring a profile for incrimination or exclusion purposes and for elucidating criminal events. This paper shows that significant quantities of DNA are frequently: (a) transferred from the exhibit to the inside of the packaging and (b) transferred from its area of initial deposit to other areas of the same exhibit and/or to other exhibits within the same package. There is a distinct possibility of failing to generate adequate profiles in instances where the DNA content may otherwise have been adequate, and for the misinterpretation of a result that could impact negatively on the criminal investigation and court outcome. These findings highlight the need for improvements in the collection and packaging of forensic casework exhibits for DNA analysis.

Aroma permeability of hydroxypropyl maize starch films.

In this study, the role of water and the impact of the glass to rubber transition on aroma mass transport through hydroxypropyl maize starch films were followed. The permeability of four aroma compounds (ethanol, pyrazine, menthone, and decanone) was monitored by atmospheric pressure chemical ionization mass spectroscopy. The increase in water content within the film promoted greater water diffusion and film flexibility and resulted in enhanced transport of the four aroma compounds through the film. At low water contents in the glassy state, the permeability of ethanol was much higher than those of the other three compounds, which was attributed to its low molecular volume and greater solubility in starch. The structural changes induced by the glass transition resulted in the hydroxypropyl maize starch films displaying poor barrier behavior in the rubbery state for all the aromas studied.

Effect of water content on the structural reorganization and elastic properties of biopolymer films: a comparative study.

In this work, the effect of water uptake on the structural reorganization and elastic properties of three types of biopolymer films was studied. The water-biopolymer interaction for hydroxypropyl cellulose (HPC), gelatin, and cassava starch films prepared from aqueous solutions was studied and compared using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction, dynamic vapor sorption (DVS), and dynamic mechanical thermal analysis with humidity generator and controller (DMTA) techniques. The FTIR spectral variations due to the water sorption were generalized into two-dimensional (2D) correlation graphs for each biopolymer, and the effect of water on the molecular conformation was compared. The water sorption isotherms were fitted with Guggenheim-Anderson-De Boer (GAB) and D'Arcy and Watt models. The water content in the mono- and multilayers predicted by both models for each biopolymer was discussed and compared. The correlation of the fitted data obtained from the sorption isotherms to the DMTA data allowed us to conclude that the elastic properties of the HPC films depended on the total water content in contrast to the elastic properties of the gelatin and cassava starch films, which decrease only with the appearance of multilayer water.

Solvent-induced lysozyme gels: effects of system composition and temperature on structural and dynamic characteristics.

The gelation process of lysozyme in water/tetramethylurea in the presence of salt was investigated as a function of temperature and system composition by rheology, infrared spectroscopy, and microcalorimetry. Times and temperatures of gelation were determined from the variation of the storage (G') and loss (G'') moduli. It was found that gelation times follow exponential decays with both protein and tetramethylurea (TMU) concentrations and with temperature. The activation energy for the overall process shows a linear dependence on TMU mass fraction. A strongly increased beta-sheet content and reduced alpha-helix occur with the increase of TMU concentration in the binary solvent. Also, a linear decrease of lysozyme denaturation temperature and enthalpy on TMU concentration is found for the TMU mass fraction up to 0.5, above which no denaturation signal can be detected.

Enthalpy relaxation of bovine serum albumin and implications for its storage in the glassy state.

Two endothermic peaks could be observed for five commercial samples of bovine serum albumin (BSA). The smaller peak observed by differential scanning calorimetry (DSC) corresponded to enthalpy relaxation. This peak was followed on storage of BSA, in its glassy state, after it had been heated above its denaturation temperature. Enthalpy and peak temperature increased with duration of storage. On storage for one week at 60 degrees C, a sample at 8.3% moisture showed a peak at 100 degrees C with an energy value of approximately 2 J per g protein. BSA samples were heated within the DSC sufficiently to eliminate the lower enthalpy peak but without altering the denaturation enthotherm. The amount of physical aging shown by these BSA samples was similar to that of the heat-denatured samples. It was concluded that the heating endotherms of dry BSA reflect both the storage and thermal history of the sample. Possible implications of the enthalpy relaxation of BSA on the behavior of this important protein are considered.

Molecular weight effects on the glass transition of gelatin/cosolute mixtures.

The structural properties of four gelatin fractions in mixture with sucrose and glucose syrup have been investigated extensively using small deformation dynamic oscillation. The total level of solids was 80%, the number average molecular weight of the protein ranged from 29.2 to 68 kD, and the temperatures were between 60 and -60 degrees C. Remarkably, the nature of the time and temperature dependence on the viscoelastic functions of all samples could be reduced to master curves using horizontal shift factors. The construction of master curves indicates a common mechanism of structure formation, which, in accordance with the synthetic polymer literature, comprises the rubbery zone, glass transition region, and glassy state. Application of Ferry's free-volume formalism and Rouse theory suggests that there is no change in the thermodynamic state of materials during vitrification, with changes in molecular weight simply introducing shifts in the time scale and temperature range of contributions to viscoelasticity. The thermorheological simplicity allowed development of the concept of "rheological" Tg. This was defined as the point between free-volume phenomena of the polymeric backbone occurring in the glass transition region and an energetic barrier to rotation required for local chain rearrangements in the glassy state. Mechanical relaxation and retardation distribution functions were calculated, thus obtaining values for the effective friction coefficient per monomer unit of the protein. It appears that the local friction coefficient is governed by a linear relationship between fractional free volume and the decreasing molecular weight of the protein, which introduces additional voids due to molecular ends.

Gelatin vs polysaccharide in mixture with sugar.

The structural behavior of a well-characterized gelatin sample has been revisited to investigate the morphology of its network in the presence of sugar. This was then contrasted with the corresponding properties of the gelling polysaccharides agarose, kappa-carrageenan, and deacylated gellan. Small deformation dynamic oscillation, differential scanning calorimetry in plain and modulated mode, visual observations, and transmission electron microscopy were used to identify the structural characteristics of the biopolymers from the rubbery plateau through the transition region to the glassy state. In contrast to the collapse of the polysaccharide gels at intermediate levels of co-solute, gelatin forms reinforced networks. The drop in polysaccharide network strength is accompanied by a decline in the enthalpy of the coil-to-helix transition, whereas the transition enthalpy is more pronounced in gelatin gels in accordance with their strengthening. Tangible evidence of the molecular transformations was obtained using microscopy, with polysaccharides disaggregating and dissolving in the saturated sugar environment. Gelatin, on the other hand, is visualized in an aggregated form thus producing a phase-separated topology with sugar.