Characterization of carbohydrate-protein matrices for nutrient delivery

Amorphous carbohydrates may show glass transition and crystallization as a result of thermal or water plasticization. Proteins often affect the state transitions of carbohydrates in carbohydrate-protein systems. Water sorption behavior and effects of water on glass transition and crystallization in freeze-dried lactose, trehalose, lactose-casein (3: 1), lactose-soy protein isolate (3:1), trehalose-casein (3:1), and trehalose-soy protein isolate (3:1) systems were studied. Water sorption was determined gravimetrically as a function of time, and Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were fitted to the experimental data. Glass transition temperature (T(g)) and instant crystallization temperature (T(ic)) in anhydrous and water plasticized systems were measured using differential scanning calorimetry (DSC). The Gordon-Taylor equation was used to model water content dependence of the T(g) values. The critical water content and water activity (a(w)) at 24 °C were calculated and crystallization of lactose and trehalose in the systems was followed at and above 0.54 a(w). Carbohydrate-protein systems showed higher amounts of sorbed water and less rapid sugar crystallization than pure sugars. A greater sugar crystallization delay was found in carbohydrate-casein systems than in carbohydrate-soy protein isolate systems. The T(g) and T(ic) values decreased with increasing water content and a(w). However, higher T(ic) values for lactose-protein systems were found than for lactose at the same a(w). Trehalose showed lower T(ic) value than lactose at 0.44 a(w) but no instant crystallization was measured below 0.44 a(w). State diagrams for each system are useful in selecting processing parameters and storage conditions in nutrient delivery applications.     

Water Sorption and Plasticization Behavior of Spray-dried Lactose/Protein Mixtures

ABSTRACT: Water sorption properties, effects of proteins on glass transition temperature, and time-dependent lactose crystallization of spray-dried lactose and lactose in lactose/WPI (3:1), lactose/Na-caseinate (3:1), lactose/albumin (3:1), and lactose/gelatin (3:1) mixtures were investigated. Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were used to model water sorption. Lactose/protein mixtures sorbed high amounts of water at low relative vapor pressure (RVP) up to 23.1%. Above 23.1% RVP levels, water sorbed by pure lactose was higher, up to 44.1% RVP, except in the case of the lactose/gelatin mixture. Lactose/ gelatin also sorbed a high amount of water at 33.2% RVP. Loss of sorbed water resulting from crystallization of amorphous lactose was observed. Crystallization of pure lactose and lactose crystallization in lactose/protein mixtures occurred at RVP ≥ 44.1% within 24 h. After crystallization at RVP ≥ 54.5%, water contents remained higher for lactose/protein mixtures than for pure lactose. The rate of lactose crystallization was less in all lactose/protein mixtures than was observed for pure lactose. WPI had the lowest effect on lactose crystallization. Crystallization occurred most slowly in lactose/gelatin mixtures. Both GAB and BET models fitted to water sorption data up to 0.441 a_w. It seems that different proteins interact with lactose differently. Water sorption and time-dependent lactose crystallization of lactose/protein mixtures have important consequences to processing and storage behavior of lactose-protein based products.     

纤维增强对镁基复合板物理力学性能的影响

以玻璃纤维为增强材料,以镁基无机矿物质为基体材料,制备了新型纤维增强镁基无机复合板.研究了短切纤维、纤维网格布以及短切纤维结合纤维网格布3种增强方式对镁基复合板的物理力学性能和耐湿热性能的影响.结果表明,纤维增强方式对镁基无机复合板的密度、含水率、吸水率等性能影响较小,对复合板的力学性能和耐湿热尺寸稳定性影响较大,采用...     

Mechanical Characterization of Individual Instant Coffee Agglomerates

Agglomerated instant coffee particles were compressed individually with a TA-XT2 Texture analyzer. Up to about 57% equilibrium relative humidity (ERH), the force-displacement curves were very jagged. The slopes of plots of highest local force peaks vs deformation were used as a measure of agglomerate stiffness. The degree of jaggedness of the original force-displacement curves, a brittleness measure, was quantified in terms of an apparent fractal dimension using two algorithms. Stiffness and brittleness were little affected by moisture at ERH levels in the range 11 to 52%. At ERH 57% both decreased sharply, indicating plasticization of the soluble material.     

Water sorption and the plasticization effect in wafers

Wafers are low moisture food products whose crunchiness or crispness is considered a primary textural attribute, highly affected by the product's physical state (glassy or rubbery). The water activity–water content–glass transition relationships for commercial wafers are reported, using Gordon and Taylor's equation to model the water plasticization effect and also Brunnaver‐Emmett‐Teller (BET) and Guggenheim‐Anderson‐DeBoer (GAB) sorption models. BET monolayer moisture content was 6.2% and the moisture limit to fit this model was about 11.5%. Critical water activity and critical water content for the glass transition of the product at 20 °C were 0.591 and 0.118 (mass fraction) respectively. Abrupt changes in the mechanical product properties, evaluated from a three‐point bend test, could be observed at these limits. Moisture levels between 6 and 11% give rise to a glassy state matrix in the product and so to acceptable product crispness. Below this range, the glassy matrix seems to turn fragile and, above this range, the product becomes rubbery.     

Physical Properties of WPI Films Plasticized with Glycerol, Xylitol, or Sorbitol

ABSTRACT: Effects of glycerol, xylitol, and sorbitol on selected physical properties of whey protein isolate (WPI) films were examined. Increasing glycerol or sorbitol content led to increases in moisture content, water vapor permeability, and % elongation; and decreases in tensile strength, elastic modulus, and glass transition temperatures of the films. Increasing levels of xylitol had no effect on permeability, moisture content, or glass transition temperature of the films, but decreased % elongation, tensile strength, and elastic modulus. Moisture content of the films correlated well with glass transition temperatures. Differences in measured physical properties of films with plasticizer type and concentration may be attributed to differences in the hygroscopic and crystalline properties of the plasticizers.     

Ergogenic Attributes of Young and Mature Coconut (Cocos nucifera L.) Water Based on Physical Properties,Sugars and Electrolytes Contents

The present work aimed to compare the main ergogenic attributes of two commercialized stages (young and mature) of coconut water (CW) obtained from four coconut varieties. The changes of electrolytes and sugars in CW upon maturation were quantified by inductively coupled plasma mass spectrophotometer and high-performance liquid chromatography, respectively. Based on the electrolyte profiling, potassium yielded the highest amount (ranging from 237.41 to 361.20 mg/100 mL) followed by sodium, magnesium, calcium, iron, manganese, copper, selenium, and zinc across all the maturity stages tested. For sugars, there were lower amounts of fructose and glucose, but a higher amount of sucrose with the maturation of the fruits. In conclusion, the amount of beneficial nutrients in the form of sugars and minerals was higher than that of young CW, and the ergogenic attributes of mature CW especially from MATAG variety (M-MATAG) were the best to be exploited further in the development of natural energy drinks.     

Effect of Sucrose on Physical Properties of Spray‐Dried Whole Milk Powder

ABSTRACT: Spray‐dried whole milk powders were prepared from whole condensed milk with various sucrose concentrations (0%, 2.5%, 5%, 7.5%, and 10% w/w), and their glass transition temperature and some physical properties of importance in chocolate manufacture were evaluated. In milk powder samples, the glass transition temperature and free‐fat content decreased in a nonlinear manner with sucrose addition. Moreover, increasing sucrose concentration reduced the formation of dents on the particle surface. Addition of sucrose in whole condensed milk increased linearly the apparent particle density and in a nonlinear manner the particle size of spray‐dried milk powders. The particle size volume distribution of milk powders with the highest sucrose concentration differed from the log‐normal distribution of the other samples due to the formation of large agglomerates. Neither vacuole volume, nor the amorphous state of milk powders was affected by sucrose addition.     

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.     

微胶囊机械性能表征方法的研究

为了对微胶囊机械性能进行定性及定量的分析,利用实验室常用的紫外可见分光光度计、抗压强度机、显微硬度仪和电子天平,研究了四种表征方法。以实验室自制的酚醛环氧树脂微胶囊为例,进行表征后发现：使用紫外可见分光光度计,借助胶囊破裂前后的吸收光谱变化,可对包有隐性染料的微胶囊进行间接定性表征;使用抗压强度机可对紧密堆积的微胶囊块进行直接定量表征;使用显微硬度仪和电子天平可实现对单个微胶囊进行直接定量表征。四种不同表征方法实现了对单个、多个微胶囊的定性和定量表征。     

Plasticizing—Antiplasticizing Effects of Water on Physical Properties of Tapioca Starch Films in the Glassy State

The effects of moisture sorption on physical properties of native and cross-linked starch films in the glassy state were studied. Water played a dual role as a plasticizer or an antiplasticizer, depending on the physical property measured. Plasticizing effects were clearly evident in the case of the calorimetric glass transition temperature ( T _g), tensile modulus, linear expansion, and water vapor permeability. In contrast, antiplasticization by water resulted in maxima in tensile strength, strain-at-break, and toughness of films that were observed at an intermediate moisture content ranging from 4% to 8% (RVP 0.1 to 0.4). The seemingly contradictory effects of water on mechanical properties associated with lower and higher deformation of starch films were reconciled by assigning different roles to water operating primarily via opposite entropic/free volume effects. Relationships, if any, between DSC thermal events and mechanical antiplasticization were not apparent.     

剑麻纤维/聚丙烯复合材料物理力学性能的研究

研究了剑麻纤维(SF)的预处理方法、长度和含量对剑麻纤维/聚丙烯(SF/PP)复合材料物理力学性能的影响,采用扫描电子显微镜(SEM)对复合材料的冲击断面进行微观结构分析.实验结果表明:SF经过碱处理和蒸汽爆破处理后,复合材料的冲击强度分别提高了70%、76%;当SF的长度为5～8 mm、含量为20%时复合材料的冲击强度达到最大为21.99 kJ/m2;SF含量为50%时弯曲强度、弯曲弹性模量与纯PP相比提高了27.5%、41.1%;熔体流动速率和吸水率随SF含量的增加变化明显.     

Characterization of Physical Properties of Flour and Starch Obtained from Gamma‐Irradiated White Rice

Physical and structural characteristics of rice flour and starch obtained from gamma‐irradiated white rice were determined. Pasting viscosities of the rice flour and starch, analyzed by using a Rapid Visco Analyser, decreased continuously with the increase in irradiation dosage. Differential scanning calorimetry showed that gelatinization onset, peak and conclusion temperatures of rice flour and starch changed slightly but the enthalpy change decreased significantly with increase of irradiation dosage. All irradiated starch displayed an A‐type X‐ray diffraction pattern like the native starch. Gel permeation chromatography showed that the blue value ratio of the first peak (amylopectin) to the second one (amylose) decreased with the increase of the irradiation dosage. The weight‐average molecular weight (M_w) and gyration radius (R_z) of amylopectin analyzed by using HPSEC‐MALLS‐RI (high‐performance size‐exclusion chromatography equipped with multiangle laser‐light scattering and refractive index detector) decreased gradually from 1.48×10⁹ (M_w) and 384.1 nm (R_z) of native rice starch to 2.36×10⁸ (M_w) and 236.8 nm of 9 kGy‐irradiated starch. The branch chain‐length distribution of amylopectins determined by HPAEC‐ENZ‐PAD (high‐performance anion‐exchange chromatography with amyloglucosidase post‐column on‐line reactor and pulsed amperometric detector) showed that gamma irradiation had no significant effect on the amylopectin branch chains with 13≤DP≤24 and 37≤DP, but produced more branch chains with 6≤DP≤12 when the irradiation dosage was less than 9 kGy. It might be deduced that gamma irradiation caused the breakage of the amylopectin chains at the amorphous regions, but had little effects on the crystalline regions of starch granules, especially at low dosage irradiation.     

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.     

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.     

Trout‐Skin Gelatin‐Based Edible Films Containing Phenolic Antioxidants: Effect on Physical Properties and Oxidative Stability of Cod‐Liver Oil Model Food

Abstract: Trout‐skin (Oncorhynchus mykiss) gelatin‐based films containing antioxidants (epigallocatechin gallate (EGCG), 50 and 250 ppm w/w) and green tea powder (1% and 20% w/w of gelatin) were tested for tensile strength, elastic modulus, and elongation, and oxygen and water vapor transmission rates, in vitro antioxidant activity using the DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) assay and effect on stabilizing cod‐liver oil held under mild thermal abuse conditions. Cod‐liver oil overlaid with films was stored at 40 °C for 20 d and analyzed for peroxide value (PV) and thiobarbituric acid reactive substances (TBARS). Antioxidant activity was retained in films containing green tea powder, but was reduced (P < 0.05) in EGCG films (20 d, 23 °C). Water vapor transmission rate of the films incorporated with antioxidants did not change significantly (P > 0.05), but the oxygen transmission rate for films with 50 ppm EGCG and 20% green tea powder was significant (P < 0.05). Other physical properties varied with antioxidant incorporation. The TBARS and PV of control oil increased from 0.05 ± 0.01 to 4.71 ± 0.30 g MDA/kg oil and from 3.6 ± 0.2 to 178.3 ± 24.5 millieq peroxides/kg oil, respectively, after 20 d. For cod‐liver oil covered with control or antioxidant‐containing films, TBARS remained below 0.37 g MDA/kg oil and PV below 7 millieq peroxides/kg oil. Incorporation of antioxidants to the films did not reduce oil oxidation (P > 0.05) at the levels tested and this was confirmed by activation energy calculations. The rate of oil oxidation was more dependent upon the inherent oxygen barrier property of the films than the presence of antioxidants. Practical Application: This research has the potential to enhance the utilization of fish skins, a valuable food processing by‐product, as edible films with natural antioxidants to extend the shelf life of foods. The film physical properties and barrier to oxygen and water are investigated.