Emako Miyoshi

Rheological and thermal studies of gel-sol transition in gellan gum aqueous solutions

Abstract The rheological and thermal properties of sodium-form gellan gum solutions with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride were studied by dynamic viscoelastic measurement and differential scanning calorimetry. Temperature dependence of the loss modulus G″ for gellan gum solutions of lower concentrations without salt showed one step-like change at a certain temperature, however, that for concentrated gellan gum solutions (> 2.0%) showed two step-like changes. The higher temperature process was attributed to the helix-coil transition, and was found in between the exothermic and endothermic peak temperatures Ts and Tm observed in cooling and heating DSC curves, while the lower temperature process was attributed to the sol-gel transition. Temperature dependence of G″ for gellan gum solutions of higher concentrations (> 3.2%) showed a large hysteresis, moreover, the temperature at which G″ showed the second step decrease in the heating process shifted to higher temperatures with increasing concentration of gellan gum. The cooling or heating DSC curves for gellan gum solutions of lower concentrations showed a single exothermic or endothermic peak, and both Ts and Tm shifted to higher temperatures, and both exothermic and endothermic enthalpies increased with increasing concentration of gellan gum. However, for a gellan gum solution with a concentration higher than 3.2%, two endothermic peaks were observed on heating while the cooling curve showed only one exothermic peak. The lower temperature endothermic peak corresponds to the first step decrease of G″ in the heating process, and the higher temperature endothermic peak corresponds to the second step decrease of G″. The viscoelastic behavior of gellan gum solutions was influenced much more strongly by divalent cations than by monovalent cations. DSC heating curves for a 1% gellan gum solution in the presence of sufficient monovalent cations showed multiple endothermic peaks, however, these multiple peaks were observed at significantly higher temperatures than those for a gellan gum solution of high concentration (3.2%) without salts. The endothermic peaks in the presence of sufficient divalent cations in the heating DSC curve were too broad to be resolved from the baseline, however, many small peaks were observed at higher temperatures and the largest endothermic peak was observed at a temperature higher than 100 °C. Therefore, although divalent cations promote the formation of thermally stable junction zones much more strongly than monovalent cations, the gellan gum gels containing divalent cations may also consist of physical junction zones of hydrogen bonds because these junction zones can be unzipped on heating to 120 °C.

Gel-sol transition in gellan gum solutions. I. Rheological studies on the effects of salts

The mechanical spectra of sodium gellan gum solutions with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride were observed at the frequency range from 10−2 to 10 rad/sec and at the temperature range from 30 to 0°C. At any temperature from 30 to 0°C, the viscoelastic behaviour of a 1% gellan gum solution without salt was typical of a dilute solution. However, that of a 2% gellan gum solution varied from a dilute solution to a weak gel with decreasing temperature. The behaviour of a 3% gellan gum solution tended towards that of a weak gel, even at the relatively high temperature of 25°C. Storage shear modulus G′ for 1% gellan gum solutions increased on addition of salts at lower temperatures where gellan molecules take helical conformations whilst it decreased on addition of salts at higher temperatures where gellan molecules take coil conformations. Salts promote aggregation of helices at lower temperatures whilst they reduce the coil dimension at higher temperatures. The increase in G′ for gellan gum solutions by the addition of cations at lower temperatures was attributed to the electrostatic shield of the repulsions between carboxyl groups, and more remarkable for potassium ions than sodium ions, and for calcium ions than magnesium ions. On addition of fairly lower concentrations of NaCl, CaCl2 or MgCl2 (except for KCl), G′ became slightly smaller than that without salt. This appears to be related to the fact that these ions deprive the hydrated water molecules surrounding carboxyl side groups in gellan gum molecules, so that the repulsion of these ‘naked’ carboxyl groups becomes stronger by the presence of these ions. However, G′ at a constant temperature and at a constant frequency for gellan gum solutions as a function of added salt concentration showed a complicated behaviour. G′ for a 1% gellan gum solution in the presence of 75 mmol/dm3 NaCl as a function of temperature increased abruptly around 55°C on cooling and showed a maximum around 35°C. On heating G′ showed a maximum around 45°C, and levelled off, and then decreased rapidly about 70°C. On the other hand, G′ for a 1% gellan gum solution in the presence of 5.1 mmol/dm3 CaCl2 began to rise rapidly at 35°C on cooling, and decreased with decreasing temperature. On heating G′ did not change remarkably up to 90°C in contrast to the situation in the presence of NaCl. This shows that the mechanism of gel formation in gellan gum with divalent cations is markedly different from that with monovalent cations.

Rheological and DSC studies on the interaction between gellan gum and konjac glucomannan

Abstract Interaction between gellan gum (GELL) and konjac glucomannan (KGM) has been studied by dynamic viscoelastic measurements and differential scanning calorimetry (DSC). Three fractions of konjac glucomannan with different molecular weights (1.17 × 10 6 (ND), 9.5 × 10 5 (LM-1) and 2.51 × 10 5 (LM-2)) were used in this study. Mechanical spectra showed that 1.6% solutions of GELL alone and of LM-2 alone behaved like a dilute polymer solution whilst 1.6% solutions of ND alone and LM-1 alone behaved like a concentrated polymer solution where molecular entanglements play an important role. Thermal scanning rheological measurements showed a step-like change in the loss modulus which is attributed to helix-coil transition, and subsequent aggregation of helices, and an exothermic and endothermic peak appeared in cooling and heating DSC curves at the same temperature of transition. The transition temperature shifted to lower temperatures, and the transition enthalpy decreased with increasing KGM content in the mixture. The elasticity of mixtures originates mainly from aggregated helices of gellan gum molecules for GELL/LM-2 systems whilst the contribution from KGM is more important for GELL/LM-1 and GELL/ND systems. Although the storage modulus of GELL/LM-1 and GELL/ LM-2 as a function of mixing ratio showed a maximum, it is concluded that KGM inhibit the formation of the ordered structure of gellan gum.

Rheological and thermal properties of milk gels formed with κ-carrageenan. I. Sodium caseinate

Abstract Mixed gels, formed by κ-carrageenan, and sodium caseinate were studied by differential scanning calorimetry (DSC) and rheometry. DSC showed that during gelation (i.e. cooling) the thermal behaviour of κ-carrageenan was almost uninfluenced by the presence of sodium caseinate. Thus the interaction of κ-carrageenan with sodium caseinate has little (or no) effect on the carrageenans coil-to-helix transition. In contrast, during melting, added sodium caseinate strongly modified the thermal behaviour. The DSC peak became progressively broader with addition of sodium caseinate, indicating that the junction zones are highly heterogeneous in the mixed gel. Rheometry showed that sodium caseinate strongly influences the storage modulus (G′). In experiments in which the concentration of sodium caseinate was fixed and that of κ-carrageenan varied, plots of G′ vs. concentration of κ-carrageenan were biphasic, with an abrupt change in slope at a concentration that increased linearly with the concentration of sodium caseinate. When the concentration of κ-carrageenan was constant and that of sodium caseinate varied, G′ as a function of concentration of sodium caseinate passed through a minimum. This behaviour could be modelled quantitatively, by assuming that: (a) the sodium caseinate adsorbs κ-carrageenan, but with a limited adsorptive capacity; (b) sodium caseinate aggregates (sub-micelles) with adsorbed κ-carrageenan can associate via interaction between free ends of adsorbed κ-carrageenan chains and form a gel network; and (c) the contributions to G′ from the sodium caseinate–κ-carrageenan network and the network formed by κ-carrageenan alone are additive. At low κ-carrageenan to sodium caseinate ratios, the sodium caseinate and κ-carrageenan combine to form a mixed gel. As the ratio of κ-carrageenan to sodium caseinate increases, the sodium caseinate becomes saturated and no further association with κ-carrageenan can occur—the increase in G′, as further κ-carrageenan is added, comes from a gel network formed by κ-carrageenan alone.

Effects of salts on the gel-sol transition of gellan gum by differential scanning calorimetry and thermal scanning rheology☆

Abstract The rheological and thermal properties of sodium form gellan gum solutions with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride were studied by dynamic viscoelastic measurement and differential scanning calorimetry. Temperature dependence of the loss modulus for gellan gum solutions of lower concentrations without salt showed a one step-like change at a certain temperature, however that for concentrated gellan gum solutions (>2.0%) showed two step-like changes. The higher temperature process Thc may be attributed to the helix-coil transition and found in between the exothermic and endothermic peak temperatures Ts and Tm observed in cooling and heating DSC curves, while the lower temperature process Tsg may be attributed to the sol-gel transition. Temperature dependence for gellan gum solutions of higher concentrations (>3.2%) showed a large hysteresis, moreover, the temperature at which the loss shear modulus G″ showed the second step decrease shifted to higher temperatures with increasing concentration of gellan gum. The cooling or heating DSC curves for gellan gum solutions of lower concentrations showed a single exothermic or endothermic peak, and both exothermic peak temperature Ts and endothermic peak temperature Tm shifted to higher temperatures, and both exothermic and endothermic enthalpies increased with increasing concentration of gellan gum. However, for a gellan gum solution of a concentration higher than 3.2%, the endothermic peak in the heating DSC curve split into two peaks, while the cooling curve showed only one endothermic peak. The lower temperature endothermic peak in the heating DSC curve corresponds with the first step decrease of G″ in the heating process of rheological measurement, and the higher temperature endothermic peak corresponds with the second step decrease of G″. The viscoelastic change of gellan gum solutions was more remarkable by the addition of K+ than Na+, and by Ca2+ than by Mg2+. The viscoelastic behavior of gellan gum solutions was influenced much more strongly by divalent cations than by monovalent cations. DSC cooling curves of gellan gum solutions showed a single exothermic peak shifting to progressively higher temperatures with increasing concentration of monovalent cations. At low concentration of monovalent cations, the DSC heating curves showed a single endothermic peak, however, with more progressive addition of salt, the endothermic peak gradually developed bimodal character and eventually split into multiple peaks. With increasing concentration of divalent cations, the exothermic and endothermic enthalpies estimated for a main peak increased up to a certain concentration and then decreased. Moreover, the endothermic peaks in the presence of sufficient salts were too broad to be resolved from the baseline, and many other peaks were observed at higher temperatures. Gellan gum solutions with sufficient divalent cations form firm gels on cooling to below the setting temperature, and then it was difficult to remelt them, which was quite different from the behavior of thermoreversible gels formed in the presence of monovalent cations.

Effects of Heat-Moisture Treatment and Lipids on Gelatinization and Retrogradation of Maize and Potato Starches

ABSTRACT Effects of heat-moisture treatment (HMT) and lipids on the structure and gelatinization of maize and potato starches were studied, and the retrogradation process of 20% HMT starch gels was also investigated. Maize starch was physically modified by HMT or by defatting. Potato starch was physically modified by HMT or by adding monoglycerides. The X-ray pattern of the HMT maize starch was assigned to a combination of A and V patterns, which indicated that HMT formed crystallized amylose complexes and recrystallized amylose in maize starch granules. However, the X-ray pattern of defatted maize starch did not change for HMT, so the lipids originally existing in starch granules were important to the formation of new crystallites during this treatment. Differential scanning calorimetry (DSC) results suggested that weaker structures in amylopectin crystallites were more susceptible to degradation after HMT, while crystallized amylose complexes developed thermal stability after treatment. The amylose cont...

Gel-sol transition in gellan gum solutions. II. DSC studies on the effects of salts

Abstract The thermal properties of sodium form gellan gum solutions with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride were studied by differential scanning calorimetry (DSC). The DSC cooling or heating curves for 1% gellan gum solutions without salt showed a single exothermic or endothermic peak at ~30°C. DSC cooling curves showed a single exothermic peak, with the setting temperature ( Ts ) shifting to progressively higher temperatures with increasing concentration of the added NaCl or KCl. At low concentrations of NaCl or KCl, DSC heating curves showed a single endothermic peak; however with more addition of salt the endothermic peak gradually developed a bimodal character and eventually split into more than two distinct peaks. The onset of detectable splitting occurred at a high salt concentration which coincided with that at which elastic gels are formed at even a higher temperature as was observed by viscoelastic measurements. With a sufficient addition of monovalent cations the endothermic curve became again a single peak shifting to higher temperatures. In the presence of divalent cations, although Ts shifted to higher temperatures with increasing concentration of added CaCl 2 or MgCl 2 , the melting temperature ( Tm ) in heating DSC curves shifted to higher temperatures (up to a certain temperature) and then shifted to lower temperatures with increasing concentration of salt. With increasing concentration of CaCl 2 or MgCl 2 , the exothermic and endothermic enthalpies estimated for a main peak increased up to a certain salt concentration and then decreased; however many other peaks were observed at higher temperatures. The endothermic peaks for gels with excessive divalent cations were too broad to be resolved from the baseline; in contrast the exothermic peaks were much sharper and readily recognized. In comparing thermal properties with rheological properties, gellan gum solutions with excessive divalent cations form firm gels on cooling to below the setting temperature, and then it was difficult to remelt them. This was quite different from the behaviour of thermoreversible gels formed in the presence of monovalent cations. It seems that the mechanism of gel formation in gellan gum with divalent cations is markedly different from that with monovalent cations.

RHEOLOGICAL AND DSC STUDIES OF AQUEOUS DISPERSIONS AND GELS OF CURDLAN

Mechanical spectra of aqueous dispersions of curdlan showed solid-like behaviour both at 40°, and at 70°, and the mechanical loss tangent for the dispersions decreased with increasing temperature. 2% dispersions heated at temperatures higher than 120° did not show any endothermic peak in the second DSC run heating curves, indicating that structures formed at higher temperatures than 120° are stable and thermo-irreversible. However, 2% dispersions prepared by heating in the temperature range from 55 to 115° were thermo-reversible. Stress-strain curves for cylindrical gels of curdlan prepared at 90° were determined.

Pragmatism and Ruskin's idea of beauty : The relativity of color and form considered from Peirce's phenomenology

In this paper, the authors have been paying their color and form in the painting art that are thought it has intrinsic value, and examining how Ruskin determined to theoretical validity about the color expression based on Peirce’s phenomenology. By the consideration, it became clear that Ruskin determined to the validity by a process of abductive inference in an idea of beauty as a guidance about whether a color as the uncertain secondary qualities of the relationship with things could embody in intrinsic value in the painting art. Furthermore, it became clear that an idea of beauty in Ruskin is placed as the ideal that is similar to esthetic goodness as the ultimate end in pragmatism.

Proactive mining system in potosi silver mines : new information from re-evaluation of historical materials regarding the fifth viceroy toledo's various policies on environment

In this paper, the proactive mining system introduced by the fifth viceroy, Francisco de Toledo (1569–1581) to the Potosi Silver Mine is clarified on the facts found in the historical documents. Main policies in Toledo’s mining business are followings, the application of mercury-amalgamation to extract silver from ores, the construction of the hydraulic-powered system for silver-ore crashing with cascading uses, the recycle system included the extraction of silver from waste ores and collection mercury by pulpprocessing. Also in the Toledo’s era, acceleration of developing Huancavelica mercury mine, and national monopolization and production control on mercury were established. And within Toledo’s mining law, there were cautionary items for pre¬venting the inhalation of mercury gas and the construction of hospitals for treatment. According to those items, the viceroy Toledo may be prominent organizer for business but because these were not technically perfect, environmental damages referred to now as mine pollution started from the colonial period and continued until modern-day period. This pollution can be found in Potosi’s air, water, and soil. The history of Potosi mine can’t be described leaving out the viceroy Toledo.