Amorphous Maltose Research Articles

Color-based clustering algorithm as a novel image analytical method for characterizing maltose crystallinity in amorphous food models

Maltose crystallization affects the processibility and stability of sugar-rich foods. This study introduced a color-based clustering algorithm (CCA) to analyze crystallinity from the images of amorphous maltose/protein models. The XRD and DSC were also implemented in maltose crystallization characterization and validated the CCA analysis. The results indicated that CCA could effectively recognize maltose crystals (R = 0.9942), and amorphous maltose mainly crystallized to anhydrate α-maltose and β-maltose monohydrate according to its morphological aspects measured by CCA, XRD, and DSC. However, protein could change the mechanism of maltose crystal formation by disturbing the mutarotation and recrystallization processes of unstable β-maltose. Besides, maltose crystal formation and crystallinity were governed by molecular mobility as the CCA-derived Avrami indexes changed with the Strength parameter. Compared to XRD and DSC, the proposed CCA can provide a rapid and quantitative measure for maltose crystallinity and has great potential applications in the online detection of sugar crystallization.

More reasons to add less salt – NaCl's unfavourable impact on glass transition and moisture sorption of amorphous maltose-NaCl blends

Adding NaCl to maltose depressed the glass transition temperature (T g ) of freeze-dried maltose-(dissociated) NaCl powder (by up to 9.1 °C at 10%mol addition level) but did not impact sorption isotherm in the water activity (a w ) range of 0.1–0.3. Above 2%mol NaCl, moisture and NaCl had an antagonistic effect on T g depression of freeze-dried maltose-NaCl powder. According to linear and Flory-Fox models, T g increased linearly with mixtures’ molecular weight. T g and sorption isotherm curves were then combined to determine the a w at which glass transition occurs at various storage temperatures (i.e. critical a w ). From the combined curve, critical a w decreased linearly with increased NaCl concentration in the mixture. Furthermore, the critical a w depression was steeper at higher temperatures. Finally, neither processing (dry mixing versus freeze drying) nor NaCl concentration affected the crystallization kinetics of amorphous maltose during dynamic humidification (0 to over 90% relative humidity) at 25 °C. • NaCl lowered the temperature and humidity at which amorphous maltose becomes sticky. • Temperature sensitivity can be predicted by amorphous mixtures' molecular weight. • Adding ≤10%mol NaCl did not affect amorphous maltose's crystallization kinetics.

Crystallization and strength analysis of amorphous maltose and maltose/whey protein isolate mixtures.

Maltose is an essential derivative of starch. To understand the processability and stability of maltose-containing foods, material characterization of the phase and state transition from its amorphous state is required. Although the crystallization of amorphous maltose is well understood, few studies have reported the relationship between the crystallization and the glass transition temperature (Tg )-related molecular mobility. In this study, water sorption, crystallization, Tg -related α-relaxation, and the corresponding time factor for amorphous maltose and maltose / whey protein isolate (WPI) mixtures are measured at various water activity (aw ) levels and 25 °C. The water-additive principle for maltose / WPI mixtures was observed at aw ≤ 0.440 at the molecular level, whereas the crystallization of amorphous maltose occurred at high aw values (≥0.534). The crystal formation and crystallization kinetics of amorphous maltose were affected by water and WPI at aw ≥ 0.534 and 25 °C, as determined by X-ray diffraction. The relationship between Tg and the water content was fitted by the Gordon-Taylor model, and its constant showed a compositional dependence for the maltose / WPI mixtures. The α-relaxation temperature of the amorphous samples decreased due to water plasticization, but increased with an increase in the WPI quantity. The Strength (S) value for amorphous maltose, which was a quantitative estimate of the compositional effects on molecular mobility, was based on the William-Landel-Ferry (WLF) equation. The S concept exhibits considerable potential for application in controlling the crystallization of amorphous maltose and improving the processability and stability of maltose-containing foods. © 2020 Society of Chemical Industry.

Effect of Water Content on the Glass Transition Temperature of Calcium Maltobionate and its Application to the Characterization of Non-Arrhenius Viscosity Behavior

To understand the fundamental physical properties of calcium maltobionate (MBCa), its water sorption isotherm, glass transition temperature (T g), and viscosity (η) were investigated and compared with those of maltobionic acid (MBH) and maltose. Although amorphous maltose crystalized at water activity (a w) higher than 0.43, MBCa and MBH maintained an amorphous state over the whole a w range. In addition, MBCa had a higher T g and greater resistance to water plasticizing than MBH and maltose. These properties of MBCa likely originate from the strong interaction between MBCa and water induced by electrostatic interactions. Moreover, the effects of temperature and water content on η of an aqueous MBCa solution were evaluated, and its behavior was described using a semi-empirical approach based on a combination of T g extrapolated by the Gordon-Taylor equation and a non-Arrhenius formula known as the Vogel–Fulcher–Tammann equation. This result will be useful for understating the effect of MBCa addition on the solution’s properties.

Water Self-Diffusion in Glassy and Liquid Maltose Measured by Raman Microscopy and NMR

Raman microscopy and isotope labeling have been used for the first time to measure water self-diffusion in carbohydrate glasses. Together with pulsed-gradient stimulated-echo NMR, this method yielded the self-diffusion coefficients of water in amorphous maltose over 8 orders of magnitude, from the liquid to the glassy state. There are consistencies and major differences between our data and those obtained by evaporative drying. Water diffusion is remarkably fast in maltose glasses, decouples from maltose diffusion, and is not strongly affected by the glass transition.

Dynamic site heterogeneity in amorphous maltose and maltitol from spectral heterogeneity in erythrosin B phosphorescence

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in thin films of either maltose or maltitol to investigate the physical properties of these amorphous pure sugar matrixes. Intensity decays collected as a function of emission wavelength over the range from 640 to 720 nm were analyzed using a stretched exponential kinetic model in which the lifetime ( τ) and the stretching exponent ( β) were the physically relevant parameters. The lifetimes varied systematically with emission wavelength in both matrixes. Analysis of the temperature dependence of the lifetime at each wavelength provided an estimate of the activation energy for nonradiative quenching of the triplet state; the activation energy also varied with emission wavelength. In addition, time-resolved emission spectra exhibited a blue shift with time following excitation. These data support a photophysical model in which probes are distributed among sites that vary in terms of overall molecular mobility and in which sites with lower rates of dipolar relaxation also have lower rates of collisional quenching of the erythrosin triplet state. The amorphous matrix of both maltose and maltitol in both the glass and the melt state is thus characterized by dynamic site heterogeneity in which different sites vary in terms of their overall molecular mobility.

Molecular Mobility in Amorphous Maltose and Maltitol from Phosphorescence of Erythrosin B

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in amorphous thin films of maltose and maltitol at mole ratios of 0.8:10(4) dye:sugar to monitor the molecular mobility of these matrixes over the temperature range from -25 to over 110 degrees C. Analysis of the emission peak frequency and bandwidth (full width at half-maximum) and time-resolved intensity decay parameters provided information about thermally activated modes of matrix mobility that enhanced the rate of dipolar relaxation around the triplet state and the rate of intersystem crossing to the ground state (k(TS0)). Detectable dipolar relaxation began in the glassy state about 50 degrees C below T(g) in both maltose and maltitol; the relaxation rate, however, while 3-4 orders of magnitude slower than literature values for the beta relaxation determined from dielectric relaxation, had an activation energy only 2-fold smaller. Dipolar relaxation was further enhanced in the melt above T(g); the dipolar relaxation rates in the melt scaled nearly exactly with rates for the alpha relaxation determined from dielectric relaxation. Intensity decays were well fit using a stretched exponential decay function in which the lifetime (tau) and the stretching exponent (beta) were the physically significant parameters. In maltose, the magnitude of k(TS0) was essentially constant in the glass and increased dramatically at the T(g); in maltitol k(TS0) increased moderately at T(g) = -50 degrees C and more dramatically in the melt at T(g) = +20 degrees C. The value of k(TS0) in maltose:maltitol mixtures was significantly smaller than that seen in pure maltose and maltitol, suggesting that specific interactions decreased the mobility of the mixed sugar matrix; this phenomenon was comparable to the antiplasticization seen in mixtures of small molecule plasticizers with synthetic polymers and starch. The extent of inhomogeneous broadening and dynamic heterogeneity were essentially constant in the glass and increased dramatically in maltose and more gradually in maltitol at the glass transition.

Volumetric behaviour of maltose–water, maltose–glycerol and starch–sorbitol–water systems mixtures in relation to structural relaxation

The densities of amorphous maltose–water, maltose–glycerol and starch–sorbitol–water mixtures were measured using a vibrating-tube density meter and pycnometry. The volumetric change on mixing was investigated through the calculation of the quantity Δ V/ V, the difference between (experimental) volume of the mixture and the linear composition weighted pure constituent volumes (ideal mixing). For all of the systems studied the quantity Δ V/ V was negative and approached a minimum of −0.03 and −0.015 at mass fractions of maltose in the region of 0.75 and 0.85 for the maltose–water and maltose–glycerol mixtures, respectively. Results are discussed in the context of volume change due to structural relaxation of vitreous materials and related to the phenomenon of antiplasticisation.

Structural relaxation and physical ageing of starchy materials

The structural relaxation during the ageing of an amorphous maltose and a starch–sorbitol mixture was examined using a range of physical techniques. Heat capacity, measured by differential scanning calorimetry, showed an overshoot in the glass-transition region, the size of which was temperature and time dependent. Volume relaxation measurements were made at different ageing temperatures in the range T g −15 to −30 K. The volume decreased with increasing ageing time, in an essentially linear fashion with log time. The mechanical behaviour of the materials showed a progressive embrittlement on ageing. For both materials, the mechanical relaxation time increased with ageing, and the material became stiffer. Investigation of the effect of physical ageing on transport properties was also performed using conductivity measurements on a maltose–water–KC1 mixture. A decay in conductivity, which was almost linear with log time, was observed. The structural relaxation was modelled using the Tool–Narayanaswamy approach to describe the calorimetric data.

Diffusion of short chain alcohols from amorphous maltose–water mixtures above and below their glass transition temperature

The apparent diffusion coefficient for short chain alcohols in undercooled maltose–water mixtures close to the calorimetric glass transition temperature, T g, was measured by following desorption using headspace gas chromatography. The plasticising effect of the alcohols on T g was characterised using differential scanning calorimetry. The initial appearance of alcohol in the headspace showed a linear dependence on the square root of time, allowing it to be modelled as a Fickian diffusive process. The diffusion coefficient decreased with increasing molecular size of alcohol and proximity to T g. Close to the glass transition the variation of diffusion coefficient with temperature and composition does not follow that of viscosity and, for ethanol, divergence was observed at T g/ T>0.88.

Carbon-13 nuclear magnetic relaxation in supercooled liquid and glassy maltose

13 C longitudinal relaxation rates (T1-1) in highly viscous liquid and solid amorphous maltose, its mixtures with water and methanol, and also crystalline maltose monohydrate, have been measured as a function of temperature, above and below the calorimetric glass transition temperatures of the amorphous materials. From the results it is concluded that, at temperatures up to 60°C below the glass transition temperature, the carbon atoms in the exocyclic hydroxymethyl groups of maltose are more mobile than the endocyclic carbon atoms. A few percent of water is sufficient to considerably enhance amorphous maltose mobility. At temperatures close to the glass transition methanol in amorphous maltose–methanol mixtures retains a high degree of rotational mobility which is decoupled from the bulk viscosity.

Study of plasticizer–oligomer and plasticizer–polymer interactions by dielectric analysis: maltose–glycerol and amylose–glycerol–water systems

Dielectric analysis was performed on amorphous maltose–glycerol and amylose–glycerol–water systems. A primary relaxation, appearing in the range of the calorimetric glass transition temperature, was observed in the maltose-glycerol system. From 0% (w/w) to approximately 30% (w/w) glycerol, a secondary relaxation was observed at lower temperature in both systems. In this concentration range, the addition of glycerol shifted the primary relaxation to lower temperature and the secondary relaxation to higher temperature. For mixtures containing around 30% (w/w) glycerol, the relaxation map revealed a merging of the primary and secondary relaxations or a disappearance of the secondary relaxation. Above 30% (w/w) glycerol in the amylose–glycerol–water system, indication of a phase separation was obtained. This behaviour is compared with the relaxation behaviour of some plasticized synthetic polymers (polyvinylchloride and polyisoprene).

Conductivity of maltose–water–KCl mixtures in the supercooled liquid and glassy states

The conductivities of low water content amorphous maltose–water–KCl mixtures have been measured using both direct current and alternating current techniques at temperatures ranging from –60 °C to 85 °C. The mixtures all contained 11.6% w/w water and between 0.0052% w/w and 0.52% w/w KCl which resulted in mixtures with a calorimetric glass-transition temperature, Tg, of –5 °C. In the supercooled region, as the temperature is reduced to Tg, the activation energy of the conductivity increases from 80–85 kJ mol–1 to 155–165 kJ mol–1 and the conductivity is found to depend upon the viscosity to the power –0.52, which indicate that the conductivity is uncoupled from the viscosity. In the glassy region, as the temperature is reduced below Tg, the conductivity falls at a reduced rate with an activation energy of 60–75 kJ mol–1, a value which is similar to the activation energy of the secondary dielectric relaxation process in the glass. Qualitatively similar conductivity behaviour has been observed in other classes of amorphous materials, such as polymers and ionic glasses. The ability of conduction measurements to probe translational mobility in supercooled and glassy states makes it suitable for investigating the effects of molecular structure and size on mobility.