Rheological properties of sodium alginate in an aqueous system during gelation in relation to supermolecular structures and Ca binding

Gelation behavior of sodium alginate was investigated in an aqueous system at various CaCO₃ doses using two alginate samples of different mannuronate (M)/guluronate (G) ratios but with comparable molecular masses. Macroscopic rheological properties of the polysaccharide were discussed during gelation in relation to microscopic supermolecular structures imaged by atomic force microscopy and Ca²⁺ binding. At fixed concentrations of the polysaccharide (0.5 w/v%) and glucono-δ-lactone (15 mM) as an acidic material, the G-rich sample was higher in elasticity with rod-like molecular assemblies at the highest CaCO₃ dose; 15 mM, while the M-rich sample was higher in elasticity with network-like molecular assemblies at the lowest CaCO₃ dose; 3.75 mM. Gelation behavior near the sol-to-gel transition was generally described by the percolation model, except for the M-rich sample at the lowest CaCO₃ dose. A critical CaCO₃ dose corresponded to 7.5 mM at which both alginate samples showed essentially the same gelation kinetics. In an equilibrium state, it was estimated that the G-rich sample was bound to larger amount of Ca²⁺ at the lowest CaCO₃ dose, while the M-rich sample was bound to larger amount of Ca²⁺ at the highest CaCO₃ dose. The amount of bound Ca²⁺ did not directly relate to elasticity of the system. Based on these results, dominant block structures are suggested for gelation.     

On fracture analysis using an element overlay technique

In this paper, an element overlay technique (s-FEM [Comput. Struct. 43 (1992) 539]) is applied to various two dimensional linear fracture problems. When s-FEM is adopted, local finite element model concerning cracks can be built independently from the global finite element mesh for modeling overall structure. The local model is superposed on the global one. Therefore, it is tractable to introduce cracks in an existing finite element model. The accuracy of s-FEM is critically examined and it is found that the size of local mesh region needs to be larger than or roughly equal to that of an element in the global mesh.     

Viscoelastic and fragmentation characters of model bolus from polysaccharide gels after instrumental mastication

Model bolus from polysaccharide gels was investigated by the stress-relaxation tests and particulate size analyses. Using two gelling agents, gellan gum and a composite of gellan/psyllium seed gums, gels with different physical properties (i.e., elastic gellan single gels and plastic composite gels) and gel hardness were prepared. Gels were masticated instrumentally in the presence or absence of artificial saliva to prepare model bolus. Data from the stress-relaxation tests analyzed by 5-element mechanical model showed that difference between two Maxwell-bodies in the elasticity for the composite gels was generally smaller than that for gellan single gels when compared at equivalent gel hardness and was less influenced by the addition level of saliva. For each gel sample, cumulative particulate size distribution of model bolus was reduced logarithmically with a normal curve regardless of the addition level of saliva. Mean particulate size of model bolus from the composite gels was generally larger than that for gellan single gels when compared at equivalent gel hardness and was less influenced by the addition level of saliva. Based on the particulate size distribution of model bolus, coefficients of skewness and kurtosis calculated for the composite gels tended to be larger than those for gellan single gels when compared at equivalent gel hardness. Results indicated higher structural homogeneity of model bolus from the composite gels, which is related to higher miscibility with saliva. Structural homogeneity should be the key for texture design of nursing-care foods, particularly for dysphagia.     

Swallowing profiles of food polysaccharide solutions with different flow behaviors

The relationship between physiological response and sensory perceived scores in swallowing was investigated using food polysaccharide solutions. Solutions from xanthan gum (0.3–0.9%) and locust bean gum (0.5–0.8%) were used as specimen with different flow behaviors identified by static and dynamic rheological methods. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. From acoustic analysis, time required for bolus to transfer through the pharyngeal phase t₂ decreased with increasing concentration of xanthan gum despite the viscosity increase. Also, the acoustic balance for the swallowing sound shifted to a higher frequency range with increasing concentration. The t₂ for locust bean gum was much less concentration-dependent and consistently larger than that for xanthan gum when compared at equivalent shear viscosity at 10 s⁻¹. Also, the acoustic balance for the swallowing sound was less concentration-dependent than that for xanthan gum. From sensory evaluation, 0.6% xanthan gum was scored the highest in perceived swallowing ease, while 0.75% locust bean gum was scored the lowest. Both t₂ and the acoustic balance correlated well with perceived swallowing ease. Results indicate that xanthan gum solutions flow as one coherent bolus through the pharyngeal phase with smaller variation of flow velocity than locust bean gum solutions, leading to a greater sensation of swallowing ease. “Structured fluid”, defined as fluid with yield stress such as xanthan gum solutions, is a rheological nature that allows bolus to be swallowed in one go, relating to perceived swallowing ease of liquid foods.     

Texture design for products using food hydrocolloids

Some in vivo measurements have been carried out using polysaccharide gels of different physical properties (i.e., elastic and plastic) and degrees of hardness. In vivo measurements tested included electromyography (EMG) and acoustic analysis of the swallowing sound to investigate the dynamic changes of food texture during oral processing. As a model of foods for dysphagia patients, the gels were soft enough to be eaten by compression between the tongue and the hard palate without biting by the teeth. From EMG, no significant differences were found between elastic gels and plastic gels in the duration of oral processing and the EMG activity of the suprahyoid musculature when compared at equivalent hardness. The EMG activity of the suprahyoid musculature correlated well with the compression load of gels at 95% strain. From the acoustic analysis, the plastic gels required shorter time to transfer through the pharynx and were scored higher in sensory cohesiveness than the elastic gels. Results indicate that oral processing of soft gels requires equivalent EMG activity of the suprahyoid musculature when the gel hardness is the same. Also, the plastic gels flow through the pharynx as one coherent bolus with smaller variation of the flow speed. Texture of foods for dysphagia patients should be optimized in terms of viscoelasticity so that they can easily transform to swallowable bolus during oral processing.     

Degradation Index for Quality Evaluation of Commercial Dietary Supplements of Bilberry Extract

In recent years, many anthocyanin‐containing dietary supplements of various dosages and formulations have been sold through advertising their large number of beneficial effects. On the other hand, there is an increased risk of distributing deteriorated supplements to consumers due to lax regulations, because in Japan these supplements are classified as food. Spectrophotometric methods are commonly used to control the quality of supplements. However, these methods have limitations with regard to assessing deterioration. In this study, we evaluated a new index for detection of deteriorated products. The stability of 3 formulations and the quality of 20 supplements were investigated by ultra‐high performance liquid chromatography, which is superior to spectrophotometry for identifying and quantifying individual anthocyanins. The stability was not only affected by storage temperature but also by formulation. We defined “Degradation Index” (DI) as an indicator of the deterioration of supplements. Of 20 supplements investigated, the DI of 5 supplements was more than 3‐fold the value of Bilberon‐25, and the worst one was 12.7‐fold. These results suggest that DI could be a useful quality control index for detecting deteriorated supplements.     

Luminescence study of europium（Ⅲ） tris（β-diketonato）/phosphonate complexes in chloroform

The extraction of Eu（Ⅲ） with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the luminescence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltfifluoroacetone, Htta, were used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extraction data, the stability constants, log β, of the first complexes between tfis（β-diketonato）Eu（Ⅲ） and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu（Ⅲ） luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu（Ⅲ）, while that in Eu（pta）3PhPO was stronger than EuA3; however, in Eu（tta）3PhPO, it was weaker than Eu（tta）3. The POPO functions as a sensitizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu（Ⅲ） luminescence in the complexes as well as the observation of the extractability of Eu（Ⅲ） with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu（Ⅲ） was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence enhancement. This phenomenon may be due the formation of a strong bond between the Eu（Ⅲ） and the strong Lewis base leading to more hydrophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu（Ⅲ）. It was not significant whether the donor atoms were N or O.     

Structural modifications of sugar beet pectin and the relationship of structure to functionality

The emulsifying properties of sugar beet pectin (SBP) were investigated in relation to its molecular structure. SBP has been subjected to an enhancement process, and this material was here compared with conventional non-enhanced SBP. The oil-in-water emulsification properties of both were compared at 1.5% concentration at pH 3.25, using 15% middle-chain triglyceride as the oil phase. Their emulsification behavior after various enzyme treatments decreased in the order: protease > arabinanase/galactanase mixture > polygalacturonase. The enzyme treatment also decreased the molecular weight of SBP. Protease degraded the high molecular weight carbohydrate–protein complex. Arabinanase/galactanase mixture was more effective in decreasing the emulsification performance than polygalacturonase. The results confirm the key role of protein as the anchor for the oil droplets and identify also the contribution of the neutral lateral chains in stabilizing emulsions by forming a hydrated layer. Protein also aggregates, which functions as a linker for the association of the carbohydrate chains consequent to the enhancement process.