Effect of Thermosonic Pretreatment and Microwave Vacuum Drying on the Water State and Glass Transition Temperature in <Emphasis Type="Italic">Agaricus bisporus</Emphasis> Slices

This study aimed to understand the micromechanism of thermosonic pretreatment and microwave vacuum drying on Agaricus bisporus. The water state and glass transition temperature (T _g ) of fresh and thermosonically treated Agaricus bisporus slices during microwave vacuum drying were studied using differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (LF-NMR), and magnetic resonance imaging (MRI). Results showed that four population groups were contained in the initial distribution of transverse relaxation time (T ₂) data of fresh A. bisporus slices: T ₂₁ (0.38–7.05 ms), T ₂₂ (9.33–32.75 ms), T ₂₃₁ (37.65–265.61 ms), and T ₂₃₂ (305.39–811.13 ms). Thermosonic pretreatment significantly decreased the initial free water content of A. bisporus sample but was accompanied by a sharp increase in its immobilized water. “Semi-bound water transfer” appeared during microwave vacuum drying (MVD) at moisture contents (X _w ) of 0.70 and 0.60 g/g (wet basis (w.b.)) for untreated and thermosonically treated samples, respectively. MVD caused dramatic changes in the water state and enhanced the T _g by decreasing the content and mobility of immobilized water in A. bisporus tissues. The mobility of semi-bound water for thermosonically and MVD-treated samples was higher than for MVD-untreated samples, resulting in T _g values decreasing by approximately 2–11.5 °C, but the uniformity of water distribution in thermosonic-treated and MVD-treated samples was better at X _w  ≤ 0.52 g/g (w.b.).     

Effect of Addition of Native Agave Fructans on Spray-Dried Chayote (<Emphasis Type="Italic">Sechium edule</Emphasis>) and Pineapple (<Emphasis Type="Italic">Ananas comosus</Emphasis>) Juices: Rheology,Microstructure, and Water Sorption

The effect of the combination of maltodextrin DE 10 (MD) and native agave fructans (FR) in concentrations of 0, 2, and 4% (w/v) on the rheological properties, microstructure, and water sorption of spray-dried chayote and pineapple powders was evaluated. A 10% (w/v) maltodextrin treatment was used as a control to compare treatments added with fructans. The scanning electron micrographs revealed spherical particles in a range from 16 to 105 μm with shrinkage, whereby greater caking and agglomeration occurred among particles in treatments with native agave fructans. The flow behavior of all juices can be described by the Bingham model with low plastic viscosities (0.0026 to 0.0030 Pa s^?1); the isotherms of the powders show a sigmoid shape pointing to the easy union of the fructans with water molecules. These types of isotherms are common for non-porous foods, and are indicative of physical adsorption in multi-layers where the adsorbate conserves its identity.     

Water sorption and glass transition temperature of spray dried açai (Euterpe oleracea Mart.) juice

Sorption isotherms and glass transition temperature (T_g) of powdered açai juice were evaluated in this work. Powders were produced by spray drying using different materials as carrier agents: maltodextrin 10DE, maltodextrin 20DE, gum Arabic and tapioca starch. The sorption isotherms were determined by the gravimetric method, while the T_g of powders conditioned at various water activities were determined by differential scanning calorimetry. As results, experimental data of water adsorption were well fitted to both BET and GAB models. Powders produced with maltodextrin 20DE and gum Arabic showed the highest water adsorption, followed by those produced with maltodextrin 10DE and with tapioca starch, respectively. With respect to the glass transition temperature, Gordon–Taylor model was able to predict the strong plasticizing effect of water on this property. Both a_w and T_g were used to determine the critical conditions for food storage, at which powders are not susceptible to deteriorative changes such as collapse, stickiness and caking.     

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 sorption characteristics and glass transition temperature of apple puree powder

The aim of this study was to characterise the influence of different foam‐mat‐drying methods on the moisture sorption characteristics and glass transition temperatures of apple puree powder. Apple puree was foamed with the addition of 2.5% egg albumin and 0.5% methylcellulose. Convective air‐drying and microwave‐drying techniques were used. Also foamed puree with and without maltodextrin (6% or 15% w/w) was freeze‐dried. Moisture equilibrium data of powders were determined by using a static desiccator method in a water activity range of 0.0–0.903. Modulated differential scanning calorimetry (MDSC) was used to obtain the glass transition temperature. No effect of drying method on sorption properties and glass transition temperatures of apple puree powders was observed. The addition of maltodextrin to the apple puree caused an increase in T_g by 10–30 °C depending on the amount of incorporated additive. Addition of maltodextrin significantly reduced the hygroscopicity of apple puree powders.     

Water Adsorption and Glass Transition of Spray-Dried Soy Sauce Powders Using Maltodextrins as Carrier

Moisture adsorption isotherm and glass transition temperature of various spray-dried soy sauce powders containing different types and concentrations of maltodextrins were studied and compared. Maltodextrins of dextrose equivalent (DE)?=?5, DE?=?10 and DE?=?15, respectively, with concentrations of 20 or 40 % (w/v) were used as carrier agents. The equilibrium moisture content was reduced with increased maltodextrin concentration, whereas it was not apparently influenced by the value of maltodextrin DE. Both the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models could be applied to simulate the moisture adsorption behaviour of the soy sauce powders. The monolayer moisture content of the powders was determined by fitting experimental data to the BET/GAB models with a _w up to 0.53, although both models could fit satisfactorily with the experimental data to a higher water activity level_. The glass transition temperatures (T _g) of the powders equilibrated under various water activities were determined using a differential scanning calorimeter. Increasing moisture adsorption of the soy sauce powders resulted in a T _g reduction, and the experimental T _g values fitted the Gordon–Taylor model well. The BET and Gordon–Taylor models were applied together to predict the critical moisture contents (i.e. 0.0464–0.0777 g water/g dry matter) and water activities (i.e. 0.032–0.241), above which the soy sauce powders become vulnerable to degradation and changes in their physicochemical properties.     

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 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.     

Glass Transition Behavior of Spray Dried Orange Juice Powder Measured by Differential Scanning Calorimetry (DSC) and Thermal Mechanical Compression Test (TMCT)

Spray drying behavior of orange juice concentrate with various levels of maltodextrin (DE 6) was studied. Five combinations of orange juice concentrate and maltodextrin (25:75, 30:70, 35:65, 40:60, and 50:50) were spray dried at 160 and 65°C inlet and outlet temperatures, respectively. The product recovered with 50% maltodextrin concentration was sticky and only 20% powder was recovered. The recovery of orange juice powder increased as the amount of maltodextrin in powders increased. The particle size and bulk density remained almost the same in all except in 50% maltodextrin powder which was slightly larger and more dense. The moisture content of spray dried powders was high and desiccated before measuring glass transition temperature. The anhydrous spray dried powders showed increased T_g values with increasing maltodextrin concentration, from 66°C in 50% maltodextrin to 97°C in 75% maltodextrin containing powders. The glass rubber transition (T_g-r) values of all the products measured using novel Thermal Mechanical Compression Test (TMCT) were higher than T_g values measured by DSC; the difference in values increased with increase in maltodextrin concentration.     

Browning,Starch Gelatinization,Water Sorption,Glass Transition,and Caking Properties of Freeze-dried Maca ( Lepidium meyenii Walpers) Powders

The browning, gelatinization of starch, water sorption, glass transition, and caking properties of freeze-dried maca ( Lepidium meyenii Walpers) powders were investigated and compared with a commercial maca powder. The freeze-dried maca powders had lower optical density (browning) and higher enthalpy change for starch gelatinization than the commercial maca. This resulted from a difference in thermal history. The equilibrium water contents of the freeze-dried maca powders were higher than those of commercial maca at each water activity ( a _w ) because of differences in amorphous part. The glass transition temperature ( T _g ) was evaluated by differential scanning calorimetry. There was a negligible difference in the anhydrous T _g (79.5–80.2 ºC) among the samples. The T _g -depression of freeze-dried maca powders induced by water sorption was more gradual than that of the commercial maca due to a difference in water insoluble material content. From the results, critical water activity ( a _wc ) was determined as the a _w at which T _g becomes 25 ºC. There was negligible caking below a _w = 0.328. At higher a _w , the degree of caking remarkably increased with a large variation depending on the samples. The degree of caking could be described uniformly as a function of a _w / a _wc . From these results, we propose an empirical approach to predict the caking of maca powders.     

Effect of gum arabic concentration and inlet temperature during spray drying on physical and antioxidant properties of honey powder

The research studied the effect of gum arabic concentration at 35, 40 and 45 % with inlet temperatures of 160, 170 and 180 °C on the physico-chemical, functional and thermal properties of honey powder enriched with aonla (Emblica officinalis. Gaertn) and basil (Ocimum sanctum) extract, wherein other parameters like concentration of aonla extract (8 %), basil extract (6 %) and feed rate (0.11 mL/s) were kept as constant. Powder recovery and glass transition temperature (T_g) showed significant increase with the increase in inlet temperatures. On the other hand hygroscopicity, tapped density, total phenolic content, antioxidant activity and vitamin C content showed inverse response to the increase in inlet temperatures. However powder recovery, T_g, total phenolic content, antioxidant activity and vitamin C content increased with the increase in concentration of gum arabic. On the basis of obtained results it can be concluded that honey powder with the concentration of 45 % gum arabic at 170 °C inlet temperature was found to be less hygroscopic with better powder recovery and overwhelming antioxidant properties.     

Impact of Hydrocolloids and Homogenization Treatment on the Foaming Properties of Raspberry Fruit Puree

The production of healthy, ready-to-eat fruit snacks by means of foam-mat drying has to face the challenge of ensuring high foam stability throughout the entire process. Foaming properties of raspberry puree whipped for 10 min with varying concentrations of potato protein isolate (2.5, 5, 10% w/w) as foaming agent were studied. Furthermore, the impact of hydrocolloids as foam stabilizers, i.e., maltodextrin (5, 15, 30% w/w) and pectin (0.1, 0.25, 0.5, 0.75, 1.0, 2.5% w/w), in combination with the variation of protein concentration as well as the impact of a homogenization treatment of fruit puree on the foam characteristics and puree properties were investigated. Foam stability was enhanced by the increase of protein and hydrocolloid concentration. Maltodextrin and pectin showed similar behavior even though pectin was used at considerably smaller concentrations. Compared to single hydrocolloid systems, the addition of pectin and maltodextrin in combination led to a further enhancement of foam stability, which offered the opportunity to simultaneously decrease the concentration of both hydrocolloids. The destruction of fruit tissue by homogenization treatment resulted in a reduction of mean particle diameters (D[4,3], D[3,2]) and a decrease of viscosity. Despite the increase in the specific surface area (A_SF) and thus, expected enhanced oxidative processes, no changes were observed for ascorbic acid and anthocyanin contents. However, the structural changes induced by the homogenization treatment significantly affected foaming properties.     

Effect of protein concentration on the surface composition,water sorption and glass transition temperature of spray-dried skim milk powders

The effects of dilution of protein content in skim milk (34–8.5% protein content), by lactose addition, on the surface composition, water sorption property and glass transition temperatures of spray-dried powders were investigated. The X-ray photoelectron spectroscopy (XPS) study of spray-dried powders showed preferential migration of proteins toward the surface of the milk particles whereas the lactose remained in the bulk. Sorption studies showed that the lower protein concentration in milk powders is linked to an increased water adsorption property and lowering of water activity (a_w) for lactose crystallization. Analysis of glass transition temperature (T_g) of the powders sorbed at different humidities showed no distinct change in T_g values, indicating the dominant effect of lactose on the glass transition temperature of all the powders.     

Steaming time effects on the moisture migration and structural properties of Chinese Northern-style steamed bread

The aim of this study was to investigate the steaming time effects on proton transverse relaxation behavior with low field 1H nuclear magnetic resonance and structural properties of Chinese Northern-style steamed bread (CNSB). Three proton populations could be distinguished at the first 4 min: T_2b (0.1–1 ms) corresponded to rigid and exchangeable protons; T₂₂ (9–21 ms) was associated with the water protons in small and large meshes of the dough microstructure; T₂₃ (69–300 ms) was assigned to the water protons on the surface of samples. The starch gelatinization began and the water turned into the integral part of the biopolymer at 6 min, forming T₂₁ (1–3 ms) fraction. The gelatinization effect was strengthened up to 8 min and supplied a more mobile microenvironment, resulting in the increase of T₂₁, A₂₁ and M₂₁. However, the gelatinization process ended at 8 min, bringing about the stabilization of T₂₁, A₂₁ and M₂₁ until 25 min. T₂₂ fraction accounted for the largest proportion during all the steaming process. All variation trends on structural properties of CNSB and T₂ relaxation parameters including T_i, A_i (relative intensity of T_i), and M_i (population abundance of T_i) indicated that 6 and 8 min were the two transitions. The gluten matrix began to be disrupted at 6 min and was quite damaged up to 8 min by scanning electron microscopy. The peaks at 15°, 18°, 20°, and 23° in X-ray diffraction patterns appeared in the first 6 min but were lost up to 8, 10, and 25 min.     

Effect of mineral fillers on mechanical,thermal and morphological properties of kenaf recycled polyethylene wood plastic composite

This contribution presents the effect of mineral filler on mechanical, thermal and morphological properties of wood recycled plastic composite (WrPC). WrPC was prepared using kenaf wood flour, recycled polyethylene (rPE) and maleic anhydride polyethylene (MAPE) with different types of mineral filler. All materials were premixed manually and fed into a twin screw extruder. The effect of graphite, mica and talc filler on impact strength, glass transition temperature (T_g), thermal degradation and morphological properties of WrPC was studied. The highest impact strength was achieved by graphite/WrPC at 6.99 kJ/m² compared to WrPC at 4.29 kJ/m². This is due to the presence of filler particles in WrPC leading to effective distribution of applied stress to overcome crack. DSC results indicated only one peak of T_g observed within 132–134 °C as a result of miscible blending. Decomposition of WrPC was slightly affected by incorporation of mineral fillers. The internal structure of WrPC with graphite/mica/talc fillers showed smooth morphology and better dispersion.     

Production and Characterization of Gelatin Spherical Particles Formed via Electrospraying and Encapsulated with Polyphenolic Antioxidants from <Emphasis Type="Italic">Momordica charantia</Emphasis>

This study dealt with the production and characterization of gelatin nanospheres and encapsulation with Momordica charantia, commonly known as bitter gourd fruit vegetable extract (BGE). The impact of encapsulation and increasing the encapsulate loading on various physiochemical characteristics of gelatin polymeric entities as well as antioxidative attributes of BGE was studied. Nanospheres were formed via an electrospraying process conducted at 20 kV, 0.5 mL/h, and 10 cm of voltage, flow rate, and emitter/collector distance, respectively. The spherical beads were encapsulated with BGE at 5 to 15% (w/w%) loading rate. Morphological analysis through scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that nanospheres could be successfully produced. Furthermore, nanosphere encapsulation of the extract was demonstrated in transmission electron microscope (TEM) micrographs. Spectroscopic analysis indicated no chemical interactions between core and wall materials. The thermal stability of encapsulated nanoparticles slightly increased and the glass transition temperature (T_g) disappeared due to increased crystallinity. Thermogravimetric graphs of encapsulated spherical beads, at all core loadings, showed an additional phase ranging from 138 to 249 °C, overlapping with the BGE’s main TGA degradation phase. The presence of this phase, which was absent from empty bead thermograms, confirmed encapsulation occurrence during electrospraying process. Furthermore, an average of 80% of antioxidative content and potency of the extract was conserved during the encapsulation process. Moreover, phenolic content and antioxidative activity of the encapsulated extract showed higher stability than extracts while stored at refrigerated and ambient conditions.     

Freezing-induced proton dynamics in tofu evaluated by low-field nuclear magnetic resonance

The main purpose of the study was to understand and interpret the effects of freezing times on the proton dynamics and chrominance of tofu. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to monitor real-time changes in microstructure and water distribution at different freezing times. The T ₂ relaxation parameters included the relative intensity (A _2i) and the population of T _2i component (M _2i). Three proton populations focusing on approximately 0.93–4.72, 25–49, and 402–505 ms were identified as T _2b, T ₂₁, and T ₂₂, respectively. The generated ice crystals damaged the hydration layer of the soybean protein and T _2b increased over the 2 h. The side chains of the soybean protein then began to unite owing to the protein’s reduced affinity for water, making the protons of the hydrophilic groups exchangeable, and resulting in decreased mobility of the T _2b fraction. The appearance of exchangeable hydrophilic group protons caused an increase in A _2b from 2 to 6 h. The subsequent increases in A _2b and M _2b 6 h later were due to access to the unfrozen free water. The water molecules (T ₂₁ fraction) changed into ice crystals, reducing A ₂₁ and M ₂₁. The disappearance of the T ₂₂ fraction peak 6 h later was attributed to residual unfrozen water molecules, with the minor component turning into ice with a fast relaxation time. The MRI results showed that the outline of the sample was blurred at 2 h and could not be detected 6 h later. Significant correlations were further detected between T ₂ relaxation parameters and color parameters. LF-NMR has great potential as a reliable tool for the study of tofu.     

Thermal transition and thermo-physical properties of potato (<Emphasis Type="Italic">Solanum tuberosum L</Emphasis>.) var. Russet brown

Potatoes are an important food in many regions of the world and are commonly used in a variety of food products. Thermal transition and thermo-physical properties of potatoes are important in order to design efficient food processes and select appropriate storage conditions. In this study, we determined the thermal transitions and thermophysical properties of raw and blanched/par-fried potato for a temperature range of ??32 to 21.1 °C. Using differential scanning calorimetry, we found an initial freezing point (T_f) at ??1.8?±?0.1 °C, an onset of melting (T_m^′) at ??9.9?±?0.2 °C and an unfreezable water content (X^′_w) for maximally freeze-concentrated raw potato at 0.21 kg water/kg potato. Corresponding values for blanched/par-fried potatoes were ??0.9?±?0.1 °C, ??11.0?±?0.2 °C and 0.18 kg water/kg potato. Results show that an increase in solids content decreased T_f of both raw and blanched potatoes. We modelled the relationship between them using the Chen model. The apparent specific heat (C_app) increased around T_f to 31.7?±?1.13 kJ/kg K for raw potato and 26.7?±?0.62 kJ/kg K for blanched/par-fried potato. For frozen raw potato at ??32 °C, thermal diffusivity (α) was 0.89?±?0.01?×?10?^?6 m²/s and thermal conductivity (k), 1.82?±?0.14 W/m K, respectively. These values were higher for frozen raw potato than for the unfrozen raw potato (0.15?±?0.01?×?10?^?6 m²/s and 0.56?±?0.08 W/m K, respectively at 21.1 °C). The apparent density (ρ) of frozen raw potato (992?±?4.00 kg/m³ at ??32 °C) was less than that for unfrozen raw potato (1053?±?4.00 kg/m³ at 21.1 °C), and a similar trend was obtained for blanched/par-fried potato (993?±?2.00 kg/m³ at ??32 °C and 1188?±?7.00 kg/m³ at 21.1 °C, respectively). This study established a correlation between thermo-physical properties and temperature. Findings may be used to inform the design and optimization of freezing processes and frozen storage for potato products.     

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