The effect of gelation on statically and dynamically freeze-cast structures

Freeze-casting is a technique used to produce structures with anisotropic porosity in the form of well-defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La_0.66Ca_0.26Sr_0.07 Mn_1.05O₃. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze-casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non-gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB^®.     

不同超声功率处理对鲢鱼肌原纤维蛋白理化特性及凝胶品质的影响

以鲢鱼为原料,研究不同功率下超声处理对鲢鱼肌原纤维蛋白及其凝胶性质的影响。结果表明：随着超声功率的增加,肌原纤维蛋白起泡性、泡沫稳定性、乳化性和乳化稳定性均呈现先增加后降低的趋势,超声功率300 W时均达到最大值;肌原纤维蛋白热凝胶的白度和持水性也随着超声功率的增大先增加后减小,在超声功率300 W时达到最大值,较未处理样品分别提高44%和27%;肌原纤维蛋白凝胶的蒸煮损失率呈现出随着超声功率的增加一直降低的趋势,在超声功率为400 W时达到最小值,较未处理样品降低13%。上述结果表明,不同功率超声波处理对鲢鱼肌原纤维蛋白及其凝胶的改性具有一定的改善作用。     

斩拌时间和凝胶化时间对微波熟制鱼饼品质的影响

以冷冻鱼糜为原料,采用微波加热工艺制作鱼饼,研究斩拌时间和凝胶化处理时间对微波熟制鱼饼品质的影响。结果表明：斩拌时间对鱼饼的凝胶特性、质构、持水性、白度和感官品质均有极显著影响（P＜0.01）;随着斩拌时间的延长,鱼饼的破断力、凹陷深度、凝胶强度、弹性、内聚性、咀嚼性和感官评分呈现先增大后减小趋势,白度呈上升趋势,持水性呈先下降后上升再下降趋势;凝胶化处理时间对鱼饼弹性影响不显著（P＞0.05）,但对鱼饼的凝胶特性、硬度、咀嚼性、内聚性、持水性、白度和感官评分有极显著影响（P＜0.01）;凝胶化处理20 min显著改善了鱼饼品质,此时鱼饼的破断力、凹陷深度、硬度、弹性、咀嚼性、白度和感官评分均达到最大值,相比未进行凝胶化处理时分别增加86.92%、38.67%、37.05%、6.94%、43.07%、3.41%和14.65%;正交试验结果表明,鱼饼的最佳斩拌和凝胶化处理工艺为斩拌6 min,凝胶化处理20 min,此条件下鱼饼的凝胶强度为2 157.53 g·mm,白度为79.72,感官评分为8.66 分。     

pH值、NaCl浓度和加热温度对猪肉匀浆物凝胶质构特性的影响

采用二次通用旋转试验设计,研究了pH值、NaCl浓度和加热温度对猪后腿肉匀浆物热诱导凝胶质构特性的影响。结果表明:不同处理条件对凝胶质构特性的影响存在差异。不同加热温度下,pH值和NaCl浓度对凝胶硬度、弹性、内聚性、胶粘性和咀嚼性影响的总体趋势一致且两者存在明显的交互作用。pH值较低时,随着NaCl浓度的增加,凝胶的硬度、弹性、内聚性、胶粘性和咀嚼性均增大;pH值较高时,NaCl浓度对凝胶硬度、弹性和胶粘性影响较小,内聚性随着NaCl浓度增加而降低。同时,随着加热温度的升高,凝胶的硬度和胶粘性增大,内聚性和咀嚼性减小,而凝胶弹性变化较小。     

13-氢过氧化-顺-9,反-11-十八碳二烯酸氧化修饰对大豆蛋白凝胶性质的影响

以13-氢过氧化-顺-9,反-11-十八碳二烯酸(HPODE)代表脂质氢过氧化物,研究脂质氢过氧化物氧化修饰对大豆蛋白凝胶性质的影响,采用质构仪、流变仪、持水性测定以及扫描电镜等方法表征大豆蛋白的凝胶性质。结果发现:蛋白质氧化造成大豆蛋白的凝胶硬度、凝胶形成温度、凝胶强度以及凝胶持水性,随着大豆蛋白氧化程度的增加,大豆蛋白凝胶的粗糙度增加,内部空隙变大,并且分布不均匀。蛋白质氧化对大豆蛋白凝胶性质的影响与HPODE浓度有关,当HPODE浓度低于0.1mmol/L时,蛋白质氧化对大豆蛋白凝胶性质的影响很小,可以忽略。     

Acid gelation of low acyl gellan gum relevant to self-structuring in the human stomach

The aim of this study was to investigate the in vitro acid-induced gelation of low acyl gellan gum. Various metabolically relevant pH environments and hydrocolloid concentrations were investigated. These resulted in very different acid structures, which were characterised by texture analysis, with Young’s and bulk moduli and work of failure being reported. The structures of the acid gels were shown to depend upon the pH and hydrocolloid concentration (c) used during their production, with a maximum in gel strength between pH 3 and 4. Both the Young’s and bulk moduli data suggest that there is a critical concentration for gelation to occur, and both parameter values displayed a gradual increase (which appears to be lower than a c² dependency) as the gellan concentration was increased.     

β-Lactoglobulin and WPI aggregates: Formation,structure and applications

The literature is reviewed on the formation and the structure of β-lactoglobulin and whey protein isolate (WPI) aggregates in aqueous solution induced by heating. The focus is on the effects of the pH and added salt. The use of β-lactoglobulin and WPI aggregates in cold-set gels, foams and emulsions, encapsulation, and films and coatings is also reviewed.     

Gelation via cationic chelation/crosslinking of acrylic‐acid‐based polymers

The gelation characteristics of acrylic‐acid‐based polymers in the presence of a range of cationic species, namely Ca²⁺, Mg²⁺ and Al³⁺, were investigated using in situ rheological measurements during photo‐polymerisation. Fourier transform mechanical spectroscopy was used to identify the gel point, using the Winter–Chambon criteria which allow the gel point to be pinpointed by establishing the sample spanning network and quantitatively determining stiffness, relaxation exponent, gel stiffness and fractal dimensions. The results showed that the gelation processes were greatly influenced by the type of cationic species that was used in the syntheses. At the gel point, more open network clusters were formed when Al³⁺ cations were used instead of Ca²⁺ cations or Mg²⁺ cations, all relating to chloride salts. Although the concentrations of the chelating/crosslinking aluminium species affected the kinetics of the gelation, the critical gel characteristics were hardly affected. Also the solubility of the chosen aluminium salt was shown to dictate the crosslinking rates and the properties of the critical gels. The extents of the reactions and the types of network formed at the gel point and beyond indicated that reactions between the Al³⁺ ions and COOH sites, from growing poly(acrylic acid) molecular chains, differ from those exhibited by Mg²⁺ and Ca²⁺ ions. All of the chelation/crosslinking reactions met the criteria of low mutation number (N_mu), such that in all cases N_mu ? 1. © 2019 Society of Chemical Industry     

From basil seed to flexible supercapacitors: Green synthesis of heteroatom-enriched porous carbon by self-gelation strategy

Basil seed-derived multi-heteroatom–doped porous carbons (BHPCs) are successfully synthesized by a facile gelation, followed by a moderate gel water/KOH coactivation process. The BHPC-700 prepared at a relatively low KOH loading and activation temperature possesses large specific surface area (1178.3 m² g⁻¹), well-defined hierarchical micro/meso porosity, and rich self-doping heteroatom functionalities (13.08 at% of oxygen, nitrogen, phosphorous, and sulfur). Electrochemical tests demonstrate that the BHPC-700–based electrode achieves an ultrahigh specific capacitance (464 F g⁻¹ at 0.5 A g⁻¹), outstanding rate performance (retaining 73.3% capacitance at 50 A g⁻¹), and superior cyclic stability (96.8% capacitance retention over 5000 cycles). Furthermore, the BHPC-700 electrodes are assembled into all-solid-state symmetrical supercapacitors. The as-assembled device gives a high energy density of 15.0 Wh kg⁻¹ at a power density of 500 W kg⁻¹ and remarkable flexibility, demonstrating great application prospects in the area of sustainable portable electronics.