Moisture‐Mediated Interactions Between Amorphous Maltodextrins and Crystalline Fructose

The effects of coformulating amorphous maltodextrins (MDs) and crystalline fructose, a deliquescent solid, on the moisture sorption, deliquescence point (RH₀), and glass transition temperature (T_g) behaviors were determined. Moisture sorption profiles of binary fructose:MD mixtures and individual ingredients were generated using controlled relative humidity (RH) desiccators and by dynamic vapor sorption techniques. Blends exhibited synergistic moisture uptake at RHs below the RH₀ of fructose, attributed to partial dissolution of fructose in plasticized MD matrices without a significant reduction in the RH₀ of the undissolved fructose. Increasing storage temperature decreased the onset RH for moisture sorption synergy. At all storage RHs, the measured T_g (2nd scan) was significantly reduced in fructose:MD mixtures compared to individual MDs, and was related to both the synergistic moisture uptake in the blends and heat‐induced ternary fructose–MD–water interactions in the differential scanning calorimeter. Differences were found between the behavior of fructose:MD blends and previous reports of sucrose:MD and NaCl:MD blends, caused in part by the lower RH₀ of fructose. The enhanced moisture sorption in blends of deliquescent and amorphous ingredients could lead to problematic moisture‐induced changes if storage conditions are not controlled.     

Glass transition phenomena in molasses

Glass transition phenomena were investigated in molasses obtained from five Australian sugar mills. The transition temperatures (midpoint), T_g, ranged from −75 to −35 °C, while the change in heat capacity was from 0.68 to 0.84 J/g⁻¹/°C. The five molasses varied in moisture, sugars and acidity, and this variation affected the T_g. The predicted T_g of the anhydrous form from the models of Fox, Pochan-Beatty-Hinman and Fried, and from a linear model shows that the molasses with the highest moisture gave the lowest transition temperature. The glass transition parameters of anhydrous sucrose, glucose and fructose did not accurately predict the transition temperatures of the molasses.     

Effect of water content and molecular weight on the moisture isotherms and glass transition properties of inulin

Inulin is being used more and more in foods due to its ability to add functionality either as a sweetener or fat replacer and also for its nutritional benefits. In this research, moisture sorption isotherms and glass transition temperature (T_g) as a function of moisture content and molecular weight for four inulins were determined. The T_g of the inulins was related to moisture content and also molecular weight. As with maltodextrins, the extent of lowering T_g was directly related to the average chain length (lower T_g with lower chain length). The sorption properties are also similar to maltodextrins, thus inulin may be useful in providing similar functionality as maltodextrins with almost no calories (1.5 kcal/g).     

Glass Transition and Crystallization of Amorphous Trehalose-sucrose Mixtures

Our objective was to investigate the glass transition and crystallization of trehalose-sucrose mixtures at various moisture contents. Samples were freeze-dried, rehumidified, and scanned with Differential scanning calorimetry (DSC) to obtain T_g values for all mixtures and pure sugars. Amorphous cotton candy samples for crystallization studies were prepared, humidified, and monitored for crystallinity as a function of time using powder X-ray diffraction (XRD). The T_g of pure dry trehalose was found to be 106 °C, while sucrose had a T_g of 60 °C. Glass transition, as expected, occurred at an intermediate temperature for sucrose-trehalose mixtures. Of the dry samples, only those containing less than 16% trehalose showed sucrose crystallization during scanning. In cotton candy made from a 25% trehalose-75% sucrose mixture, humidified to 33%, sucrose did not crystallize after 30 days, whereas pure sucrose cotton candy at that humidity crystallized completely after 11 days. These data show that trehalose may be a useful crystallization inhibitor in foods with high sucrose content, although small amounts of trehalose did not significantly raise the T_g.     

Calorimetric study of the glass transition occurring in aqueous glucose: Fructose solutions

Glass transition temperatures (T_g) for dilute and concentrated glucose: fructose: water solutions have been determined by differential scanning calorimetry. The supplemented phase diagrams (glucose: fructose 1:4, 1:2, 1:1, 2:1, 4:1 (w/w)) are presented and from these the temperature (T_g') and concentration (C'_g) of the maximally freeze-concentrated glass have been determined. Theoretical predictions of T_g for binary (glucose: fructose) and tertiary (glucose: fructose: water) systems according to the Couchman–Karasz and Gordon-Taylor equations are given and discussed. Annealing vitrified glucose: fructose glasses above their T_g allows the glass concentration to approach C'_g as a result of ice formation. Viscosity measurements of fructose and fructose: glucose mixtures allow for a calculation of T_g of the non-aqueous solutions.     

Water and Molecular Weight Effects on Glass Transitions in Amorphous Carbohydrates and Carbohydrate Solutions

The effects of water, freeze-concentration and effective molecular weight (M_e) on glass transition (T_g) of maltose and maltodextrins were studied, and methods to predict T_g were used to establish state diagrams. T_g of maximally freeze-concentrated solutes (T′_g) and onset of ice melting (T′_m) increased with M_e, and for high molecular weight polysaccharides T′_g and T′_m were predicted to have the same temperature value. Ice formation at T′_gm was time dependent. Unfrozen water in maximally freeze-concentrated matrices was about 20% independently of M_e. The state diagrams can be used to evaluate physical state of frozen and dehydrated foods.     

Residual Moisture Content as Related to Collapse of Freeze-dried Sugar Matrices

Amorphous sugars were prepared by freeze-drying 20% (w/w) aqueous solutions of lactose, sucrose, trehalose and maltose. The dried samples were further dehydrated over P₂O₅ for 1 wk at 25, 35 or 45°C, and the residual moisture content was determined using oven drying or a thermogravimetric balance. Results indicated a small amount of residual moisture (usually 1–2%) which was not removed by the desiccation treatment for 1 wk at 25°C over P₂O₅. The dried samples, heated at a temperature near the published “anhydrous” glass transition temperatures (T_g) exhibited different behavior depending on whether they were heated in open or sealed vials. Structural collapse, a sharply visible shrinkage of the matrix, was found in all samples in sealed vials, while those samples in open vials did not collapse. Thus, removal of the last amount of residual moisture by heating in uncovered vials increased T_g, preventing or delaying collapse.     

Physicochemical, mechanical and thermal properties of brown rice grain with various moisture contents

The effects of moisture content on the mechanical and thermal properties of either a short‐grain variety (Akitakomachi) or two long‐grain varieties (Delta and L201) of brown rice were studied. Total starch contents of the three varieties were comparable, but the amylose content of L201 was significantly higher than that of the other two varieties. The maximum compressive strength of brown rice grain was much higher than the maximum tensile strength. L201 showed the highest maximum compressive and tensile strengths. The phase transition temperatures (glass transition temperature T_g and melting temperature T_m) were examined by differential scanning calorimetry. The T_g and T_m for L201 were higher than those for Delta and Akitakomachi. The maximum compressive strength, maximum tensile strength, T_g and T_m for the three varieties of brown rice grains decreased with increasing moisture content. The T_g of individual brown rice kernels decreased from 53 to 22 °C as moisture content increased from 12 to 25% wet basis. A statistical model was calculated by using linear regression to describe the change in T_g in terms of moisture content.     

Glass Transition and Sticky Point Temperatures and Stability/Mobility Diagram of Fruit Powders

Principal components present in fruits are low molecular weight sugars and some organic acids. They have low glass transition temperature (T _g) and are very hygroscopic in their amorphous state, so the dry product becomes sticky. Water acts as a plasticizer and decreases the glass transition temperature of the product with the increase in moisture content and water activity. To overcome this problem, ingredients having high T _g value, such as maltodextrin, and food grade anti-caking agents were added to prepare vacuum dried fruit powders. The relationship between T _g and a _w provides a simple method for prediction of safe storage temperature at different relative humidities environment. Food powders namely, mango, pineapple, and tomato (3–4% w.b moisture content) were produced by mixing with maltodextrin and tri calcium phosphate at predetermined levels before drying. The relationship among glass transition temperature (T _g), sticky point temperature (T _s), moisture content and water activity of the three powders was represented in a stability/mobility diagram to find out safe storage conditions. Glass transition temperature of the fruit powders were interpreted in terms of the Gordon-Taylor model for verification. Glass transition and sticky point temperatures were compared by plotting them in a graph against moisture content.     

Pulse NMR Study of Glass Transition in Maltodextrin

A pulse nuclear magnetic resonance (NMR) technique was used to study the glass transition in maltodextrins. The spin-lattice relaxation time (T₁ and spin-spin relaxation time (T₂) of different molecular weight maltodextrins at different moisture contents and temperatures were measured using the pulse NMR tech nique. T₁, and T₂ were plotted against temperatures. From the resultant curves, the state transitions were observed and the corresponding state transition temperatures were determined. The state transition temperatures were very close to the glass transition temperatures (T_gs) determined with differential scanning calorimetry, suggesting a strong relationship between glass transition and proton relaxation behavior. Results indicate pulse NMR-based instrumentation could be very effective for the study of glass transition in food polymers.     

Effects of Drying Air Temperature on the Structural Properties of Garlic Evaluated During Drying

Second order phase transitions may occur in foodstuffs during the convective drying process. These transitions involve physicochemical changes, which influence both structural properties and drying behavior. The aim of this study was to examine the effects of drying air temperature and the second order phase transition of garlic on the changes in particle density, apparent density, apparent porosity, effective diffusivity, and cracking produced during drying. Garlic slices were dehydrated at three air temperatures (40, 50, and 60°C). The moisture content (X), inside temperature (T_i), surface temperature (T_s), apparent (ρ_b) and particle (ρ_p) densities of garlic slices were measured during drying. Porosity (?) was calculated based on the data collected for ρ_p and ρ_b. Glass transition temperatures (T_g) and micrographs were obtained for both raw and dehydrated garlic. A critical point in the intersection of T_i, T_s, and T_g was found; this point was identified as a second order phase transition. Diffusivity and slope changes in ρ_b, ρ_p, and ? with respect to moisture content were found to be related to this critical point. Experimental data for ρ_b, ρ_p, and ? was fitted to a nonlinear equation with three exponential terms with respect to moisture content, with an R² > 0.85. Less dense products were found to be more porous, with more cracking, higher moisture diffusivity, and lower T_g at the end of the drying process.     

Crystallization of Amorphous Lactose

Crystallization of amorphous lactose was studied at constant water content and at constant relative humidity above glass transition temperature (Tg). The rate of crystallization was followed using differential scanning calorimetry. Crystallization at constant water content increased the amount of water in the remaining amorphous matrix, which decreased T_g and accelerated crystallization. At constant relative humidity crystallization proceeded at a rate determined by T -T_g which increased with crystallinity. Temperature dependence of time to complete crystallization was confirmed to follow Williams-Landel-Ferry (WLF) equation. The results can be used to evaluate diffusion and crystallization kinetics of amorphous carbohydrates.     

Amino Acids as Plasticizers for Starch-based Plastics

Amino acids of differing hydrophobicity were tested as plasticizers in starch-glycerol (4:1 weight ratio) blends and were compared to the more conventional plasticizers, urea, sucrose and ammonium chloride. In mechanical tests (tensile strength and percent elongation) on extruded ribbons containing up to 20 weight percent plasticizer, glycine and isoleucine hydrochloride were found to be extremely poor plasticizers. However, lysine behaved similarly to sucrose. Proline compared favorably to urea. Moreover, at concentrations of 23 and 29 weight percent, proline was superior to urea in its ability to increase the percent elongation of the starch-glycerol mixture. The glass transition temperature (T_g) for the standard starch-glycerol samples was 40°C, as determined by differential scanning calorimetry. Added lysine hydrochloride, sucrose, proline and urea effected the T_g similarly. At 5 weight percent all T_g's increased, while at 20 weight percent they dropped to room temperature or below. Isoleucine, at low or high concentration, yielded a T_g of 60°C, consistent with very brittle material. Biodegradation experiments were conducted on selected formulations by monitoring CO₂ evolution after inoculation with Aspergillus niger. Little CO₂ accumulated from the standard starch-glycerol mixture or sucrose plasticized blends, likely due to a lack of combined nitrogen. In contrast, proline and urea-plasticized blends were rapidly metabolized.     

Glass Transition Study in Model Food Systems Prepared with Mixtures of Fructose,Glucose, and Sucrose

Abstract: The glass transition temperature of model food systems prepared with several glucose/fructose/sucrose mass fractions was studied using differential scanning calorimetry (DSC). A distance‐based experimental design for mixtures of 3 components was used to establish the proportion of sugars of the model systems. Thus, 32 compositions including individual sugars and sugar mixtures, both binary and ternary were prepared and analyzed. Thermograms showing the complete process of heating–cooling–reheating were used to determine the precise glass transition temperature during cooling () or reheating () in amorphous sugars. The Scheffe cubic model was applied to experimental results to determine the influence of sugar composition on the glass transition temperature (P < 0.05). The final model proved to be appropriate (R² > 0.97, CV < 9%, model significance <0.0001) to predict the T_g values of any dry mixture of amorphous fructose, glucose, and sucrose. Practical Application: The experimental values of T_g and the mathematical model proposed in this work may be of great use for making available T_g data that involves the mixture of more than 2 sugars and thus could be used as a tool for predicting the storage stability and quality of dehydrated products such as fruit powders.     

Rheological evaluation of gelatin–xanthan gum system with high levels of co-solutes in the rubber-to-glass transition region

Effects of moisture content, xanthan gum (XG) addition, and glucose syrup (GS):sucrose ratio on the gelation of gelatin-XG systems with high levels of co-solutes were investigated in the rubbery and the glass transition regions. Frequency sweep tests were performed between 0.1 and 100 rad and the storage (G′) and loss (G″) moduli of the system were measured in the temperature range of 60 to −15 °C. The onset of glass transition region increased with decreasing moisture content. The time–temperature superposition yielded master curves of G′ and G″ as a function of timescale of measurement. G″ and G″ were superimposed with the horizontal shift factor a_T, which was temperature dependent according to the Williams–Landel–Ferry (WLF) equation. Glass transition temperature (T_g) of the samples were determined by dynamic mechanical analysis (DMA) from the peak of tan δ. T_g decreased with XG addition. The energy of vitrification of samples with XG increased compared to samples containing only gelatin. Relaxation spectra of the samples were calculated from rheological measurements using the first and second approximations. The Rouse theory was more closely followed with the second approximation.     

The effect of starch gelatinization and solute concentrations on T g′ of starch model system

The effect of starch gelatinization on glass transitions in a starch/water model system and how the concentrations of added solutes (sucrose and sodium chloride) affect the glass transition temperatures of the gelatinized starch solution was investigated. The starch suspension samples were heat treated in a Differential Scanning Calorimeter (DSC) under different time and temperature regimes to achieve different degrees of gelatinization. The gelatinization characteristics (onset, peak and end temperatures and enthalpy) and the glass transition values of a potato starch were determined using the DSC. The results showed that the starch concentrations had no effect on gelatinization characteristics and the T_g′ of the gelatinized potato starch but had clearly increased their ΔC_p in the T_g′ region. Annealing at a temperature slightly below the T_g′ of −5 °C, led to maximal freeze‐concentration in the total/partial gelatinized starch and a higher T_g′ value at about −3 °C was obtained. The T_g′ values of the totally gelatinized starch samples were slightly lower than those of partially gelatinized samples. The T_g′ of the gelatinized starch decreased with increasing concentrations of sucrose or sodium chloride. Sodium chloride had a stronger depressing effect on T_g′ than sucrose. © 2000 Society of Chemical Industry     

Glass Transition Explanation for the Effect of Polyhydroxy Compounds on Protein Denaturation in Dehydrated Solids

Dehydrated proteins are frequently subjected to thermal stress in the presence of other components. The effect such substances may have upon protein structure, and therefore function, has not been fully investigated. Thus, the effect of added polyhydroxy components on the denaturation of lyophilized β-lactoglobulin, ovalbumin, and ribonuclease, as determined by differential scanning calorimetry, was evaluated. The denaturation temperature, T_m, of the globular proteins decreased in the dry state after the addition of sucrose, sorbitol, or glycerol. The thermal stability (based on T_m) of the dehydrated proteins appeared to correlate with the glass transition temperature (T_g) of the polyhydroxy component, which was assumed to be related to the T_g of the mixture. The lower the T_g of the component, the greater was the degree of protein destabilization. Thus, glass transition data may be used to predict the effect that a component would have on denaturation of dehydrated proteins at elevated temperatures.     

INFLUENCE OF TEMPERATURE AND RELATIVE HUMIDITY ON THE PHYSICAL STATES OF COTTON CANDY

Cotton candy is made by melting crystalline sucrose above 210C in a bowl which shoots molten liquid sucrose into the air where it rapidly cools and dries into an amorphous glassy solid state. As such, it is highly hygroscopic, picking up moisture as %RH increases and becoming rubbery. The glass transition line (T_g vs. %RH) divides the two states. When rubbery, cotton candy should collapse forming crystalline sucrose becoming unsaleable. Cotton candy was stored at 25C and at %RH from ～0% to 75%. Moisture gain/loss, visual observations, and powder X‐ray diffraction using a Seimens 5005‐powder X‐ray diffractometer were used to evaluate collapse and crystallization. At ～0% and 11% RH (below T_g), cotton candy maintained a stable structure for at least 12 months. At 33% RH (just at T_g), it collapsed and crystallized within 3 days while at 45, 54 and 75% RH, collapse and crystallization occurred in less than 1 day.     

Thermal and rheological properties of the supersaturated sucrose solution in the presence of different molecular weight fractions and concentrations of dextran

In our current research work, we investigated the effects of molecular weight (M _w) and the concentration of dextran presence during cane sugar manufacturing on the rheological and glass transition properties of supersaturated sucrose solution. Three dextrans of various M _w, namely 100,000 g/mol (T ₁₀₀), 500,000 g/mol (T ₅₀₀) and 2,000,000 g/mol (T ₂₀₀₀), were admixed in concentrations between 1,000 and 10,000 ppm with 65 and 75% w/w sucrose solution. The results indicated that both the apparent viscosity and dynamic modulus increased with an increase in dextran concentrations and they demonstrated strong dependence on its M _w. Glass transition temperature (T _g) of the samples was measured by differential scanning calorimetry, and their dependence on dextran M _w and concentration was analyzed by the Fox and expanded Gordon–Taylor mathematical models. It was found that the higher the M _w and concentration of the dextran, the greater the increase in T _g. The expanded Gordon–Taylor equation has proved useful in predicting the T _g of the sucrose solution in the presence of polymer.     

Glass Transition State Diagram of a Baked Cracker and Its Relationship to Gluten

The polymer science approach can be applied to the understanding of physical changes in foods such as loss of texture upon moisture gain. The glass transition temperature (T_g) of a commercial cracker was measured by Dynamic Mechanical Thermal Analysis (DMTA) as a function of water content. The final state diagram showed that the cracker was plasticized by water with a glass transition temperature that decreased as water content increased. When compared with published glass transition data on cereal ingredients, gluten may be the main component responsible for the mechanical changes and loss of crispness of such products when moisture content is increased.