Frozen State Transitions in Freeze-Concentrated Lactose-Protein-Cornstarch Systems

Differential scanning calorimetry study of frozen state transitions of mixtures of lactose, proteins, cornstarch, and water revealed that maximum freeze-concentration was achieved by annealing at temperatures T′_m-1. The onsets of glass transition of maximally freeze-concentrated solids, T′_g, were lower and onsets of ice melting, T′_m, were higher for mixtures of proteins and polysaccharide than those of lactose. The established state diagrams showed solids concentrations C′_g, of the maximally freeze-concentrated systems of, 82, 78, 78, 78, and 75% for lactose, lactose/albumin, lactose/gelatin, lactose/cornstarch, and lactose/cornstarch/gelatin solutions, respectively. The state diagrams established with experimental and predicted T_g values are useful in characterization of thermal phenomena and physical state of the systems at various water contents and in the freeze-concentrated state.     

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.     

State diagram of salmon (Salmo salar) gelatin films

BACKGROUND: A state diagram presents different physical states of a biomaterial as a function of solid content and temperature. Despite their technological interest, little information is available on protein systems such as gelatin/water mixtures. The objective of this work was to develop state diagrams of salmon gelatin (SG) and bovine gelatin (BG) in order to determine maximal freeze concentration parameters (T′_g, T′_m and X_s′) and to relate possible differences to their biochemical characteristics. RESULTS: Biochemical characterisation of SG showed lower molecular weight and iminoacid concentration compared with BG. Likewise, the glass transition temperature (T_g) was lower for SG at X_s > 0.8, which was associated with its lower molecular weight. Unexpectedly, the depression of freezing temperature (T_f) was greater for SG at X_s > 0.1, which was associated with its higher ash content. Isothermal annealing produced effective values of T′_g ≈ ? 52 °C, T′_m ≈ ? 46 °C and X′_s ≈ 0.6 for both gelatins. Interestingly, the enthalpy change associated with T′_m (ΔH) was significantly higher for SG than for BG after annealing, indicating a higher proportion of ice present at about ? 50 °C. CONCLUSION: Maximal freeze concentration parameters were similar between the two gelatins, though differences in biochemical properties were evident. The results show that there are likely different ways of interaction of SG and BG with water. Copyright © 2011 Society of Chemical Industry     

Physical changes induced by the Maillard reaction in a glucose–glycine solution

Some physical changes associated with the development of Maillard reaction in a glucose–glycine aqueous solution were detected by means of thermal and rheological analysis as well as by more conventional determinations. The increase in water content, water activity (A_w) and enthalpy of ice melting (ΔHm) during the reaction reflects both the formation of new water molecules and the consumption of low molecular weight species. The concomitant arrangement of more complex molecular structures was indicated by changes in the glass transition temperature of the maximally freeze-concentrated solution (Tg′) and of the freeze-dried solution (Tg _(dry)) as well as in the estimated unfrozen water (UFW). After fractionation of the samples by solid phase extraction, the non-polar fractions exhibited much higher Tg_(dry) than the non-fractionated samples. The Tgs_(dry) of samples at increasing heating time were treated with the Gordon–Taylor equation and results were discussed. The expected increase in viscosity due to polymerisation was compensated by the formation of water, but it could be detected when viscosities were measured on samples equilibrated at a same A_w     

Solid-state tyrosinase stability as affected by water activity and glass transition

The effects of water activity (a_W) and the state of the system as dictated by the glass transition temperature (T_g) on tyrosinase storage stability were evaluated in a model food system. Tyrosinase was incorporated into low and high molecular weight polyvinylpyrrolidone (PVP-LMW and PVP-K30, respectively). Samples were equilibrated and stored in desiccators from a_W 0.33 to 0.77 at 20°C. Tyrosinase activity was monitored for a week, and pseudo-first order rate constants for activity loss were calculated. Residual activity after equilibration correlated with T_g rather than a_W. An apparent rate constant increase slightly above T_g was observed and rate constants were the same at constant T_g, suggesting that molecular mobility as dictated by T_g was influencing tyrosinase storage stability.     

Impact of arabinoxylan with different molecular weight on the thermo‐mechanical,rheological, water mobility and microstructural characteristics of wheat dough

The aim of this study was to investigate the effects of arabinoxylan with different molecular weight on the wheat dough thermo‐mechanical, rheological, microstructural and water mobility properties. Arabinoxylan was extracted from wheat bran and hydrolysed by endo‐1,4‐β‐xylanase (EC 3.2.1.8 from Trichoderma reesei, 10 000 U g^?1) for 2 min (AX_M) and 10 min (AX_L), respectively. The addition of hydrolysed arabinoxylan AX_L increased the stability time, decreased the setback value of wheat dough and enhanced the values of storage modulus (G′) and loss modulus (G″), while unhydrolysed arabinoxylan (AX_H) reduced these values. Meanwhile, unhydrolysed arabinoxylan increased T₂ relaxation time while hydrolysed arabinoxylan AX_L decreased T₂₁ and T₂₂. Confocal laser scanning microscope (CLSM) results showed that the addition of hydrolysed arabinoxylan AX_L promoted the formation of a more compact and continuous protein network in wheat dough. These results revealed that compared with high molecular weight arabinoxylan, hydrolysed arabinoxylan could improve the rheological properties and processing properties of wheat dough by enhancing the interaction among water molecules, starch and gluten in wheat dough.     

Phase Transitions and Unfreezable Water Content of Carrots, Reindeer Meat and White Bread Studied using Differential Scanning Calorimetry

Differential scanning calorimetry was used to measure the phase transitions and unfreezable water of carrots, reindeer meat, and white bread. The incipient melting point (T_im), incipient intensive melting point (T′_im), the onset temperature of melting (T_m), latent heat of melting (ΔH_m), specific heat (C_p) and enthalpy (ΔH) were determined from the melting curves. T′_im, T_mΔH_m and ΔH and the unfreezable water were found to be functions of moisture. The T_im, temperatures were ? 39°C, ?33°C, ?40°C; T′_im, ?11.8°C, ?13.3°C ?17.3°C T_m, ? 3.4°C, ? 3.1°C, ? 12.2°C for carrot, reindeer meat, and white bread, respectively. The unfreezable water was 8.3% for carrots, 15.1% for reindeer meat, and 22.5% for white bread, determined from ΔH_m and 3.4%, 6.4% and 2.9%, determined from ΔH. The lowest water detectable from ΔH_m was 26.4% and from ΔH 3.6%.     

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 transitions for freeze-dried and air-dried tomato

Glass transition temperatures of freeze-dried tomato conditioned at various water activities at 25 °C were determined by differential scanning calorimetry (DSC). Air-dried tomato with and without osmotic pre-treatment in sucrose/NaCl solutions was also analyzed. Thermograms corresponding to the low water activity domain (0.11 ⩽ a_w ⩽ 0.75) revealed the existence of two glass transitions, which were attributed to separated phases formed by sugars and water and other natural macromolecules present in the vegetable. Both transitions were plasticized by water and experimental data could be well correlated by the Gordon-Taylor equation in the low-temperature domain, and by the Kwei model in the high-temperature domain. For higher water activities, the low-temperature glass transition curve exhibited a discontinuity, with suddenly increased glass transition temperatures approaching a constant value that corresponds to the T_g of the maximally freeze-concentrated amorphous matrix. The unfreezable water content was determined through the melting enthalpy dependence on the moisture content.     

The glassy state phenomenon in applications for the food industry: Application of the food polymer science approach to structure–function relationships of sucrose in cookie and cracker systems

This review of the glassy state phenomenon in applications for the food industry comprises two main parts. The first is a broad but brief overview of the so-called ‘food polymer science’ approach and its importance to food R&D studies of glassy solid and rubbery liquid states and glass transitions in food products and processes. The following elements of this approach are discussed: (i) the glass transition temperature (T_g) and methods for its measurement in foods; (ii) plasticization by water and its effect on T_g; (iii) the concepts of ‘water dynamics’ and ‘glass dynamics’ in non-equilibrium food systems; (iv) Williams–Landel–Ferry kinetics in the rubbery state above T_g, (v) state diagrams; and (vi) the effect of molecular weight on T_g. A comprehensive and up-to-date listing of more than 400 literature references on the glassy state phenomenon and glass transitions in food materials and systems is featured in that part of the paper, and these references are also compiled and tabulated according to specific subject headings. The second part of this review highlights the application of the food polymer science approach in recently reported studies on the structure–function relationships of sucrose in cookie and cracker systems. This part describes (i) the sucrose–water state diagram as a tool in understanding cookie and cracker baking; (ii) shortcomings of the traditional AACC sugar-snap cookie method as a test-baking system, in contrast to a new test system based on a model commercial-type wire-cut cookie formula; and (iii) a revealing illustration of sucrose functionality in cookie baking. The review concludes with a word about future prospects.     

Effect of oligomeric or polymeric additives on glass transition,viscosity and crystallization of amorphous isomalt

The main purpose of this study was to further improve the stability of the amorphous state of isomalt by the addition of high molecular weight compounds. Differential scanning calorimetry (DSC) was used to determine the glass transition temperature T_g of a series of polyol mixtures containing isomalt as a function of water content. As expected, for each mixture T_g decreased with increasing moisture. Only with the addition of more than 75% of higher molecular weight compounds to isomalt an increase of T_g could be achieved. Moisture content and time dependent phase transitions in the metastable amorphous state of the mixtures strongly affect the storage stability of isomalt hard candies. Storage tests indicated a markedly accelerated water absorption and crystallization when oligomeric or polymeric compounds were added to amorphous isomalt. Rheological experiments showed that in contrast to pure isomalt melts, the viscosity of melts containing oligomeric or polymeric additives deviated from the model curve predicted by the Williams–Landel–Ferry-kinetics (WLF) with increasing water content.     

State transitions and freeze concentration in trehalose-protein-cornstarch mixtures

State transitions of solutions of mixtures of trehalose, albumen, gelatin, and cornstarch were studied and state diagrams were established. Maximum freeze concentration was achieved by annealing of solutions at a temperature −1 °C. The onset temperatures of glass transitions of maximally freeze-concentrated solutes, , were lower and onset temperatures of ice melting, , were higher for mixtures of trehalose, proteins and cornstarch when compared with those of pure trehalose. Solute concentration in the maximally freeze-concentrated phase, , was 79% for trehalose, trehalose/albumin (1:1), and trehalose/cornstarch (1:1). The of trehalose/gelatin (1:1), and trehalose/cornstarch/gelatin (1:1:1) was 74% and 75%, respectively. The state diagrams established with experimental and predicted T_g values are useful for characterization of thermal phenomena and physical state of carbohydrate-protein-polysaccharide mixtures at various water contents.     

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.     

Rheological characterization of konjac glucomannan in concentrated solutions

Dynamic viscoelasticity measurements were performed for concentrated solutions of konjac glucomannan in an ionic liquid. The entanglement coupling appeared in the rheological data for each solution was characterized in terms of the molecular weight between entanglements (M _e) as an average size of the transient entanglement network. The value of M _e for konjac glucomannan in the molten state was estimated to be 1.8 × 10³ (in g mol^?1), being significantly smaller than that for cellulose, although the molecular weight and linkage of the repeating units were the same between these polysaccharides. This result suggested that the configuration of the repeating monosaccharide unit affected the entanglement network of these polysaccharides reflecting the single chain characteristics.     

A MODEL SYSTEM FOR DIFFERENTIATING BETWEEN WATER ACTIVITY AND GLASS TRANSITION EFFECTS ON SOLID STATE CHEMICAL REACTIONS

Recent debates have emerged on whether water activity (a_w) or the state of the system as dictated by the glass transition temperature (T_g) controls the rates of chemical reactions in reduced-moisture solid systems. Previously, model systems in which the effects of water activity and glass transition on chemical reactions could be evaluated independently did not exist. The use of polyvinyl-pyrrolidone (PVP) of different molecular weights allows the water activity and moisture content of the systems to be kept virtually constant while the glass transition temperature varies. At a given water activity and temperature, the equilibrium moisture content for any molecular weight of PVP differed by only 1–2%, while the T_g values differed by 20–30C. Using PVP of different molecular weights as a model system will allow the effects of water activity and glass transition on chemical reactions to be studied independently and at a constant temperature.     

Effect of Pomace Drying on Apple Pectin

The effect of temperature used for drying apple pomace on apple pectin characteristics, including chemical composition, color and gelpoint temperature (T_g) was determined. Pomace was obtained from commercial Granny Smith apples and dried in a rotary drier at different air temperatures (T_dr = 60, 70, 80 and 105 °C). Pectin was extracted from dried pomace in nitric acid solution (pH = 2.5) at 80 °C. Major minerals in apple pectin were Ca>Na>Mg. Galacturonic acid content (% AGA=60.6±1.8) was practically unaffected by drying temperature. Conversely, T_dr affected both the degree of methoxylation (DM) and the molecular weight (M_w) of extracted pectin. M_w was estimated by applying the Mark Houwink - Sakurada equation, through determination of intrinsic viscosity of pectin solutions. M_w reduced withT_dr from approximately 122,000 (60°C) to 57,000 (105°C). Pectin color, as Hunter ΔE, was also affected by T_dr. A lighter color was obtained at 80°C. The higher gelpoint value (T_g= 80°C) was obtained with pectin from pomace dried at 80°C. Gelpoint was shown to be more sensitive to T_dr than other quality parameters: while DM had the same value both at 80 and 105°C, minimumT_g occurred at the higher temperature. T_g was also very sensitive to pH.     

Frozen State Transitions of Sucrose-Protein-Cornstarch Mixtures

ABSTRACT: State transitions of solutions of mixtures of sucrose, albumen, gelatin, and cornstarch were studied using differential scanning calorimetry, and state diagrams were established. Maximum freeze concentration was achieved by annealing of solutions at a temperature T'_m of⁻¹°C. The onset temperatures of glass transitions of maximally freeze-concentrated solutes, T'_m, were lower and onset temperatures of ice melting, T'_g, were higher for mixtures of sucrose, proteins, and cornstarch when compared with those of pure sucrose. Solute concentrations in the maximally freeze-concentrated phase, C'_g, were 80% and 81% for sucrose and sucrose/albumin, respectively. The C'_g of sucrose/gelatin, sucrose /cornstarch, and sucrose/cornstarch/gelatin was 76%. The state diagrams established with experimental and predicted T_g values are useful for characterization of thermal phenomena and physical state of carbohydrate-protein mixtures at various water contents.     

Plasticizing Effect of Water on Thermal Behavior and Crystallization of Amorphous Food Models

Dehydrated sugar solutions were used as models of thermal behavior of amorphous foods, and of the effect of temperature, moisture content and time on physical state of such foods. The transition temperatures determined were glass transition (T_g), crystallization (T_cr) and melting (T_m) which all decreased with increasing moisture. T_g of a sucrose/ fructose model had a slightly lower value than the empirical “sticky point,” at all moisture contents studied. Crystallization of sucrose was delayed by addition of fructose or starch. Crystallization above T_g was time-dependent, and the relaxation time of this process followed the WLF equation.     

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.     

Physicochemical properties of commercial starch hydrolyzates in the frozen state

The physical properties of commercial starch hydrolyzate (varying in dextrose equivalent values, DE, from 0.5 to 42) solutions in the frozen state were related to their composition. At 20% (w/v) hydrolyzate concentration, an inverse linear relationship between DE and apparent glass transition temperature (T_g′) of the unfrozen solute matrix was observed. The T_g′ temperatures remained relatively constant for solute concentrations below 40% (w/v); above this concentration the T_g′ was depressed, possibly due to the plasticizing effect of additional water entrapped in the glassy state during non-equilibrium freezing. Simple predictive models (based on the Flory–Fox equation; 1/T_g=∑{w_i/T_gi}) were found to predict reasonably well the T_g′ value of ‘binary’ monodisperse and polydisperse hydrolyzate mixtures of varying proportions between the two components. Linear relationships were also found between T_g′_measured (by calorimetry) and T_g′_predicted (based on the Flory–Fox model, and using the oligosaccharide composition of the hydrolyzates and the respective T_g′ values of the pure components). The rate of oxidation of ascorbic acid has been measured in the presence of starch hydrolyzates at temperatures between −4 and −16°C. Both the Arrhenius and WLF (Williams–Landel–Ferry) kinetic models were found to describe the temperature dependence of reaction rate constants reasonably well. However, knowing the T_g′ value of the amorphous maltodextrin was not sufficient to predict its cryostabilization behavior.