Glass transition and caking of spray-dried lactose

Simple test methods to determine the onset temperatures of viscous flow and caking of spray-dried amorphous lactose are described. The extent of viscous flow was measured as an increase in the density of lactose plugs within a cylindrical aluminium compaction apparatus after incubation for 3h at a specified temperature. Caking was characterized by an increase in the hardness of the lactose plugs formed. The onset temperature of viscous flow decreased with increasing water activity, A_w, and corresponded to the onset temperature of glass transition, T_g1. Glass transition temperatures were determined using both differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spin relaxation. The results suggest that elevation of the powder temperature above T_g1 promotes viscous flow and increases the potential for caking of amorphous food powders.     

Glass transition and crystallization behaviour of freeze-dried lactose-salt mixtures

Glass transition temperatures were determined for dehydrated lactose/salt mixtures with various water contents and water activities, and state diagrams were established. Crystallization behaviour was studied for pure amorphous lactose stored at various relative water vapour pressures (RVP). Furthermore, glass transitions temperatures and time-dependent lactose crystallization of freeze-dried lactose and lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂ and lactose/KCl mixtures in molar ratios of 9:1 were determined. Glass transition temperatures (T_g) of lactose powder as determined by differential scanning calorimetry (DSC) was lower than that of lactose/CaCl₂ (9:1)_, and lactose/MgCl₂ (9:1), but it was slightly higher than the T_g of lactose/NaCl (9:1), and lactose/KCl (9:1). Lactose/KCl had the lowest glass transition temperature, but it had about the same crystallization temperature as lactose/NaCl, and lactose/MgCl₂. The glass transition temperatures decreased as water contents increased. The critical water contents and water activities at 23 °C were predicted using data on glass transition temperature and water sorption. Pure lactose had a different critical water activity and water content from lactose/salt mixtures. The critical values of lactose/CaCl₂ (9:1) were the highest. Loss of sorbed water, indicating lactose crystallization, was observed in lactose and lactose/salt mixtures stored above the critical RVP.     

Glass transition and water effects on sucrose inversion in noncrystalline carbohydrate food systems

The effects of water and glass transition on the hydrolysis of sucrose by invertase in noncrystalline carbohydrate systems were investigated. Maltodextrin/sucrose (2:1) and maltodextrin/lactose/sucrose (1:1:1) were dissolved in distilled water. Invertase (10 mg/17.2 g) was added. Amorphous samples were produced by freeze-drying the solutions. Sorption isotherms were determined gravimetrically at 24 °C over the 0.113–0.763 a_w, and over 0.239–0.764 a_w, the glass transition, T_g was determined using differential scanning calorimetry (DSC). DSC and water sorption results suggested that samples remained noncrystalline. Sucrose inversion was analysed by monitoring glucose content during storage. Sucrose hydrolysis occurred at significant rates at 0.662 and 0.764 a_w. The rate increase was not related to the apparent glass transition of the systems.     

Glass transition behaviour of fructose

The glass transition temperature and the second transition (the endothermic change between the glass transition and melting temperatures) of fructose were studied. The thermal history strongly affected both transitions of fructose. Storage for 10 days at 22 °C increased the dynamic glass transition temperature from 16 to 25 °C and decreased the second transition of fructose from 110 to 98 °C in the first differential scanning calorimetric (DSC) scan. The amplitude of the second transition increased slightly with storage time and reached 260% of the first transition for vacuum oven dried samples. The effect of thermal history on the glass transition temperature of fructose can be removed by scanning the sample in a DSC to 130 °C. The effects of water content, glucose and sucrose on the two transitions were also investigated.     

Effect of maltodextrins in the water-content-water activity-glass transition relationships of noni (Morinda citrifolia L.) pulp powder

Water sorption behaviour at 25 °C and the water content (x_w)-glass transition temperature (T_g)-water activity (a_w) relationship was determined for noni pulp powder obtained by spray-drying with and without maltodextrin (DE 9-12), at three different MD/noni solid ratios of 1.17, 1.3 and 2.5, in order to know the effect of MD in the powder stability, preventing powder stickiness. The obtained isotherms were sigmoidal and the Guggenheim-Anderson-deBöer (GAB) model was fitted to the experimental data. The glass transition temperatures (T_g) of the different noni powders and maltodextrin in DE 9-12 were obtained using differential scanning calorimetry (DSC). The equilibrium water content of noni samples containing maltodextrin at a given water activity was lower than that obtained for the maltodextrin-free noni powder. At 25 °C, the critical water content that ensures the glassy state of the noni pulp during storage increased from 0.047 to 0.06 g water/g product when the maltodextrin/noni ratio was greater than 1.3, while the critical water activity increased from 0.13 to nearly 0.5.     

Moisture-induced caking of beverage powders

BACKGROUND: Beverage powders can exhibit caking during storage due to high temperature and moisture conditions, leading to consumer dissatisfaction. Caking problems can be aggravated by the presence of sensitive ingredients. The caking behaviour of cocoa beverage powders, with varying amounts of a carbohydrate sensitive ingredient, as affected by climate conditions was studied in this work. Sorption isotherms of beverage powders were determined at water activities (a_w) ranging from 0.1 to 0.6 in a moisture sorption analyser by gravimetry and fitted to the Brunauer–Emmett–Teller (BET) or the Guggenheim–Anderson–de Boer (GAB) equation. Glass transition temperatures (T_g) at several a_w were analysed by differential scanning calorimetry and fitted to the Gordon–Taylor equation. Deduced T_g = f(a_w) functions helped to identify stability or caking zones. Specific experimental methods, based on the analysis of mechanical properties of powder cakes formed under compression, were used to quantify the degree of caking. Pantry tests complemented this study to put in evidence the visual perception of powder caking with increasing a_w. RESULTS: The glass transition approach was useful to predict the risks of caking but was limited to products where T_g can be measured. On the other hand, quantification of the caking degree by analysis of mechanical properties allowed estimation of the extent of degradation for each product. CONCLUSION: This work demonstrated that increasing amounts of a carbohydrate sensitive ingredient in cocoa beverages negatively affected their storage stability. Copyright © 2011 Society of Chemical Industry     

Effect of maltodextrin on the stability of freeze-dried borojó (Borojoa patinoi Cuatrec.) powder

The adsorption isotherms (20 °C) and the relationship between water content and glass transition temperatures were modeled in freeze-dried borojó powder studying the effect of the addition of two maltodextrins with different dextrose equivalent (DE). Both compositional and physicochemical analyses of borojó pulp were performed. At room temperature (20 °C), the critical water content that ensures the glassy state of the product during storage increased from 5.9 g water/100 g product to 8.5–9.1 g water/100 g product when maltodextrins were added, without there being any significant differences related to the different DE. The critical water activity also increased from 0.285 to 0.504–0.510, being the borojó powder with maltodextrins added more stable.     

乳粉中的玻璃化相变及对乳粉品质的影响

在无定形聚合物玻璃化相变理论的基础上 ,介绍了乳粉中乳糖的玻璃化相变及测定方法 ,讨论了玻璃化相变的影响因素以及对乳粉品质的影响     

Effect of Encapsulating Materials on Water Sorption,Glass Transition and Stability of Juice From Immature Acerola

Immature acerola juice was dehydrated by spray drying, using as encapsulating material maltodextrin DE25, arabic gum, or a mixture of both in different proportions. A constant ratio of 1:1 was kept between juice solids and encapsulating material. The effect of encapsulation materials on water sorption, glass transition, and physical properties of encapsulated immature acerola juice was investigated. The monolayer moisture of the encapsulated juices, calculated according to the GAB theory, varied from 5.11 to 5.73g H₂O/100g of solids (25°C). The glass transition temperature (T_g) of maltodextrin and gum arabic varied from 60 (a_w 0.33) to 38°C (a_w 0.54), and from 62 (a_w 0.33) to 42.6°C (a_w 0.54), respectively. The addition of juice to the encapsulating materials decreased the T_g of the juice powder to 39.5–41.3°C (a_w 0.33) and 1.84–8.05°C (a_w 0.54), but no marked differences were found among the juice powders. The critical a_w, i.e., the point of onset of physical alterations in the encapsulated materials, was higher than the corresponding monolayer values. Stickiness was observed at temperatures close to T_g, and collapse occurred at temperatures of 20°C or more above the T_g. Maltodextrin DE25 and gum arabic offered equivalent contributions to the stability of the system.     

Glass Transition of Rainbow Trout and Its Oxidation Stability During Storage

Glass transition of rainbow trout muscle was measured by differential scanning calorimetry (DSC) as ?13°C. Sucrose and sorbitol (2, 2), sucrose and mannitol (2, 2), sucrose and gum arabic (2, 0.15), sucrose and carrageenan (2, 0.15), sorbitol and mannitol (2, 2), sorbitol and gum arabic (2, 0.15), sorbitol and carrageenan (2, 0.15), mannitol and gum arabic (2, 0.15) and mannitol and carrageenan (2, 0.15) were blended with ground rainbow trout as g/100 g fish and stored for 6 months separately at ?9°C, ?13°C and ?18°C. Total volatile basic nitrogen (TVB-N) and Thiobarbituric acid-reactive substances (TBARS) were determined at 1^st, 3^rd and 6^th months of storage periods. Biopolymers blends, storage temperature and storage period had a significant effect (p < 0.05) on the TVB-N and TBARS values.     

Glass transition and state diagram for freeze-dried Agaricus bisporus

Sorption isotherms and state diagram of freeze-dried Agaricus bisporus were developed to further investigate the connection between the two distinct criteria of food stability. Sorption isotherms of freeze-dried A. bisporus were determined by the gravimetric method and the data were modeled by GAB model. The GAB monolayer moisture content was calculated to be 6.2 g/100 g (d.b.). The glass transition temperature of freeze-dried A. bisporus was determined by differential scanning calorimetry. The state diagram was composed of the freezing curve and glass transition line, which were fitted according to Clausius–Clapeyron model and Gordon–Taylor model, respectively. The state diagram yielded maximally-freeze-concentrated solutes at 0.704 solids with the characteristic temperature of glass formation being −77.9 °C. The state diagram and sorption isotherms of freeze-dried A. bisporus are useful in evaluating the storage stability as a function of temperature and moisture content as well as optimizing drying and freezing conditions.     

Influence of the Material and the Surface Roughness of the Drying Support on the Self‐detachment of Maltodextrin Films

The influence of four different materials (glass, stainless steel, polytetrafluoroethylene – PTFE and polyamide) used as a paste drying support on the detachment conditions of dried maltodextrin films was investigated. The tests were accomplished in a drying chamber that allows the spreading of a uniform film of pastelike material over solid plates and the visual observation of the instant of the detachment from the surface. The chamber temperature and the water content of the dried film were compared with the corresponding glass transition temperature curve. The effect of the material roughness on the detachment of the dried maltodextrin film was evaluated comparing glass plates with two different surfaces (smooth and sand‐blasted glass). Results indicate that the higher the surface roughness, the drier should the film be, in order to promote self‐detachment at the same temperature conditions. The chemical and physical interactions between the support material and the dried film also influence the process. The PTFE support required less severe detachment conditions than solids with lower surface roughness.     

Determination of glass transition temperature of beef and effects of various cryoprotective agents on some chemical changes

Sucrose (2%), sorbitol (2%), mannitol (2%), gum arabic (0.15%), carrageenan (0.15%) and meat stabilizer (0.5%) were blended with ground beef and stored for 6 months separately at -9°C, -13°C (glass transition temperature (T(g)) of beef determined by Differential Scanning Calorimetry (DSC)) and -18°C. Total volatile basic nitrogen (TVB-N) and Thiobarbituric acid-reactive substances (TBARS) were determined at 1, 3 and 6th months of storage. Cryoprotectants and storage period had a significant effect (P<0.05) on the TVB-N and TBARS values. Although there were no statistically significant differences between storage at -13°C (T(g)) and -18°C, storage at -9°C had different effects on TVB-N and TBARS.     

Glass transition of pomegranate skin,as analyzed by thermal,mechanical, and nuclear magnetic resonance methods

Glass transition of pomegranate skin was measured by thermal, mechanical, and magnetic resonance techniques. Differential scanning calorimetry thermogram showed a shift (i.e., onset glass transition at 20°C) followed by an endothermic peak (i.e., solids-melting peak at 165°C and enthalpy 140 kJ/kg). Overlapping of the glass transition and melting was observed in the differential scanning calorimetry thermogram; however, more sensitive modulated differential scanning calorimetry allowed to separate two transitions (i.e., glass transition from reversible and melting from non-reversible thermograms). The onset of mechanical glass-rubber transition from differential mechanical thermal analysis was observed at 122°C with a shift in the storage modulus (E′); however, the onset of liquid-like or entangled-reaction dominating transition was observed at 70°C (i.e., onset peak in loss modulus, E′′) and peak at 184°C. In addition onset peak in tan δ was observed at 113°C and peak at 201°C. Spin–spin (T₂ relaxation) and spin-lattice (T₁ relaxation) relaxations in time domain nuclear magnetic resonance was modeled by two-exponential relaxation curve (i.e., rigid and flexible domains). T₂ relaxation showed maximum peak with an onset at 40°C with maximum peak at 150°C. Rigid domain of T₁ relaxation showed a minimum peak onset at 40°C and a minimum peak at 120°C, whereas flexible component showed an onset at 20°C and a minimum peak at 160°C.     

Glass transition temperatures and some physical and sensory changes in stored spray-dried encapsulated flavors

Commercial spray-dried powder flavors (strawberry and orange) encapsulated in different amorphous matrices (maltodextrin and maltodextrin-sucrose) were stored for 20 days under constant relative humidities of 32%, 43%, 58% and 75%. Glass transition temperatures (T_g) of the different powders and maltodextrin DE 12 were measured using differential scanning calorimetry (DSC). Caking/collapse visual observations and aroma strength (measured by a trained sensory panel) were recorded and correlated with the glass transition temperature of the different spary-dried flavors. Glass transition data explained collapse occurrence and loss of aroma strength in encapsulated strawberry and orange flavors after storage at various relative humidities.The presence of sucrose in the carrier formulation negatively affects storage stability of the encapsulated flavor.     

Caking and Stickiness of Dairy-Based Food Powders as Related to Glass Transition

The effects of heating rate, storage temperature and water activity on surface caking (T_sc) and advanced caking (T_ac) of several dairy-based infant formula powders were determined by the modified ampule and sealed glass test tube methods, respectively. The glass transition temperature, T_g, was determined by differential scanning calorimetry. Observed T_sc and T_ac values were higher at faster scan rates (5 and 10°C/min) compared to a slower heating rate (1°C/3 min). In addition, because of the sample size and the difference in viscous flow time constants, T_ac≥ T_sc≥ T_g. As expected, stability towards collapse and sticking decreased with Increasing amounts of low-molecular-weight carbohydrate. The predicted stable storage water activities at room temperature based on T_sc were higher than those observed during storage; however, the water activity at which T_starage= T_g gave a good prediction of the %RH when collapse begins.     

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.     

Glass Transition of Extruded Wheat,Corn and Rice Starch

Commercial wheat, corn and rice starch were extrusion cooked under a specific mechanical energy input (SME) ranging from 81 to 365 Wh/kg (288 to 1314 kJ/kg). Extrusion cooking at low and high SME resulted in products having significant differences in molecular weight distribution and having crystalline structures of the V‐ and E‐type, as determined by gel permeation chromatography and X‐ray diffraction analysis. Differential scanning calorimetry revealed that the glass transition temperature (T_g) of the extruded starches was independent of the botanical source, the degree of extrusion‐induced molecular fragmentation and the formation of the V‐ and E‐type crystalline structures. The obtained master curve, defined by the relationship between water content and T_g of the amorphous starch, may be used as a predictive tool in modelling the extrusion process of starch or starch containing blends, especially with regard to the formation of the morphological structure and texture attributes of directly expanded products.     

Phase behaviour of gelatin/polydextrose mixtures at high levels of solids

This investigation focuses on understanding the phase behaviour of gelatin when mixed with polydextrose (co-solute) primarily at high solid concentrations. The experimental work was carried out using small deformation dynamic oscillation in shear, modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, wide angle X-ray diffraction and environmental scanning electron microscopy. A progression in the mechanical strength and thermal stability of the gelatin network was observed with the addition of polydextrose to the system. Combined thermomechanical and microscopy evidence argues for the development of phase separation phenomenon between protein and co-solute in high-solid preparations, where gelatin maintains helical conformation to provide network integrity as well as glassy consistency at subzero temperature. At the high solids regime, glassy consistency was treated with theoretical frameworks from the synthetic polymer research to pinpoint the glass transition temperature of the system.