制备条件对结冷胶流体凝胶形成的影响

采用热剪切法制备低酰基结冷胶流体凝胶,考察基体质量浓度、降温速率、剪切速率、离子种类、离子浓度和葡萄糖酸-δ-内酯(glucono-δ-lactone,GDL)对流体凝胶的影响,并探究低酰基结冷胶流体凝胶的微观结构。结果表明,基体质量浓度越高,体系转变温度越高,形成流体凝胶的黏度、粒子粒径和不规则度增大。剪切速率越大,流体凝胶的最终黏度越小,粒径越小。降温速率越大,转变温度越低,流体凝胶的粒径越大,对低酰基结冷胶体系而言,存在一个临界降温速率,当降温速率超过该临界值时,体系的转变温度基本保持不变。该临界降温速率随着基体质量浓度的增大而降低,当基体质量浓度为0.005 g/mL时,临界降温速率为9℃/min,当基体质量浓度为0.015 g/mL时,临界降温速率则为4℃/min。离子浓度越高,体系的转变温度越高,流体凝胶的最终黏度和粒径越大,相比于钠离子,钙离子诱导流体凝胶的最终黏度更大。GDL质量浓度越高,体系转变温度越高,流体凝胶黏度越大,质地越疏松。     

大豆花生豆腐脑的凝胶性研究

以大豆、花生为主要原料,通过浸泡、磨浆、热处理、混匀和凝固等工艺制备复合豆腐脑。以蛋白质的溶出率为指标分析大豆的浸泡条件,以凝胶强度为指标分析复合豆腐脑的制备工艺条件。结果显示,大豆蛋白质的最佳溶出条件为0.4%浓度的NaHCO3、浸泡16h、1∶8（g/mL）的固液比。配比为1∶1的大豆花生混合浆料的最佳凝固条件为：固液比1∶8（g/mL）,温度85℃,时间20min,葡萄糖酸-δ-内酯（GDL）的添加量0.4%。在该条件下形成的复合豆腐脑凝胶强度在20～25g,稳定性好。     

低酰基结冷胶-乳清蛋白混合凝胶的凝胶特性

研究了离子种类、离子浓度和基体浓度对低酰基结冷胶/乳清蛋白混合凝胶力学性质、保水性质、光学性质和网络孔径的影响。研究发现,乳清蛋白浓度对混合凝胶凝胶特性影响较小。混合凝胶的断裂应力、断裂应变、不透明性和保水性随着低酰基结冷胶浓度的增大而增大,混合凝胶网络孔径则随着低酰基结冷胶浓度的增大而减小。离子种类和离子浓度对混合凝胶凝胶特性影响显著,混合凝胶的断裂应力和孔径随着离子浓度的增加出现了先增大后降低的变化趋势,断裂应变和保水性则随着离子浓度的增大而减小。离子浓度增大,混合凝胶的不透明指数随之升高,当离子浓度超过某一定值后,不透明指数则基本保持恒定。相对于钠离子而言,钙离子形成的凝胶更强且用量更少。钠离子和钙离子在诱导凝胶形成上不存在协同效应。     

马铃薯淀粉和豌豆淀粉复配体系的流变与凝胶特性研究

以马铃薯淀粉和豌豆淀粉按照一定的比例进行复配,采用动态流变仪和质构仪测定复配体系的糊化、流变特性及凝胶强度。结果表明:复配体系的糊化温度随着马铃薯淀粉比例的增大而有所下降,由70.1℃降低到64.6℃;在淀粉质量分数为6%的体系中,马铃薯淀粉和豌豆淀粉的比例为1∶5和1∶11时复配体系的弹性模量G′较大(分别为810.1 Pa和814.7 Pa),而在比例为1∶3或1∶5时复配体系的粘性模量G″较大(分别为41.0 Pa和41.6 Pa);马铃薯淀粉和豌豆淀粉的比例为1∶5和1∶11时复配体系的Tanδ较小,此配比的两个复配体系具有较好的凝胶形成能力,且凝胶强度较大(98.5~100.1 g)。     

酸诱导鱼糜凝胶的酸化条件研究及凝胶特性分析

以葡萄糖酸内酯(GDL)为酸化剂,研究温度和时间等凝胶化条件对酸诱导鱼糜凝胶理化性质的影响。结果表明:随着凝胶化温度从30℃升高到50℃,酸化速率升高,凝胶pH达到稳定所需要的时间缩短,GDL诱导鱼糜凝胶的凝胶强度逐渐下降,失水率逐渐上升。化学作用力结果表明GDL诱导鱼糜凝胶网络结构主要是通过疏水相互作用维持,且与凝胶强度趋势相一致。总巯基含量随着温度的升高逐渐升高,说明二硫键含量逐渐降低。SDS-PAGE结果显示GDL诱导鱼糜凝胶MHC条带强度受温度影响较小。当凝胶化条件为30℃、3.5h时,可通过电镜扫描观察到一个致密均匀的网络结构。说明合适的凝胶化温度和时间可以显著提高鱼糜凝胶的质构特性,促使鱼糜形成一个致密均匀的网络结构。     

GDL诱导乳蛋白酸凝胶特性的研究进展

综述了国内外GDL(葡萄糖酸-δ-内酯,Glucono-δ-lactone)诱导乳蛋白质酸凝胶特性的研究方法,并分析了影响凝胶特性的主要因素。目前,研究乳蛋白酸凝胶特性的方法主要有测定凝胶的流变学特性、凝胶的脱水收缩的能力以及凝胶的质构等。乳蛋白在酸凝胶过程中不仅受到GDL添加量的影响,还受到凝胶温度、预热处理及离子强度的影响。     

酸诱导大豆蛋白凝胶动态变化与流变特性

利用小变形震荡流变(SAOS)分析大豆蛋白酸诱导过程中的流变性质,考察GDL浓度、大豆蛋白浓度、温度对大豆蛋白冷凝胶形成过程中储能模量(G′)和损耗模量(G″)的影响,同时用色差亮度变化表征凝胶过程的动态变化。试验结果表明:室温(25℃)下,随GDL含量(0.5%~3%)的增加,8%的蛋白质聚集体溶液p H值迅速下降,G′和G″迅速增加,凝胶强度增大,耗散因子(tanδ)在0.2左右,形成弱凝胶体系;蛋白质含量(1%~7%)和冷却过程(95~25℃)显著影响凝胶强度,且蛋白质浓度越高,形成凝胶的G′值越大,强度越高。冷却过程中氢键和范德华力的形成进一步增强了凝胶强度。在凝胶过程中,浊度增大,用色差仪准确测量其亮度值,从光学角度研究酸诱导凝胶的动态变化行为。     

大豆蛋白乳状液酸凝胶的制备及表征

主要以高稳定性的大豆蛋白乳状液为原料,通过葡萄糖酸内酯（GDL）诱导形成凝胶。实验主要研究了乳状液油体积分数的变化对油滴粒径的影响以及油体积分数的变化对大豆蛋白乳状液酸凝胶的流变性质、质构和乳清分离的影响。结果表明：在此实验的油体积分数研究范围内,随着油体积分数的增大,大豆蛋白乳状液的油滴粒径增大。大豆蛋白乳状液的油体积分数越大,形成凝胶的时间越短,但是凝胶pH越高,酸凝胶（pH4.6）的强度越大。此外,油体积分数增大,大豆蛋白乳状液酸凝胶的硬度增大,乳清分离减小。     

酸化处理对真鲷鱼糜凝胶性能的影响

本实验以真鲷鱼糜为原料,通过探讨酸处理条件（温度和时间）、巴氏杀菌条件、葡萄糖酸内酯（glucono-δ-lactone,GDL）添加量对酸化鱼糜凝胶性能的影响,旨在开发出一种冷藏即食的鱼糜制品。结果表明：酸化温度为35 ℃,处理时间为1.5 h时鱼糜凝胶的破断力、破断距离和凝胶强度分别达到最大值524.23 g、1.019 7 cm和534.26 g·cm;热处理条件为68 ℃,45 min时,鱼糜制品在达到食品安全卫生标准的同时又具有较好的凝胶品质;随着GDL添加量的增加,鱼糜凝胶的破断力、凝胶强度、白度均呈上升趋势,而持水性逐渐下降;结合正交试验的初步研究结果,得到较优酸化工艺为：GDL添加量2.10%、酸化温度35 ℃、酸化时间2.0 h。     

明胶—多糖共混凝胶的研制

以明胶、甘薯淀粉、海藻酸钠等为研究对象,以凝胶强度为指标,探讨了明胶-多糖凝胶形成条件。通过比较pH、蛋白质和多糖配比因素对凝胶性能的影响,对明胶-多糖体系凝胶形成的分子力作了初步探讨。结果表明:1)明胶/甘薯淀粉体系的凝胶形成条件为基质浓度9.0%,质量比1∶1,pH5,加热温度80℃,加热时间30 min,在此条件下形成凝胶的强度为2 038 g。2)明胶/海藻酸钠体系的凝胶形成条件为基质浓度3.0%,质量比1∶1,pH5,加热温度60℃,加热时间30 min,在此条件下形成凝胶的强度为611 g。     

高酰基结冷胶的溶胶和凝胶特性研究及结构初步分析

采用黏度计和质构仪对高酰基结冷胶的溶胶和凝胶性质进行研究。结果表明：高酰基结冷胶在质量浓度为 0.05～0.1g/100mL 时,表观黏度随质量浓度增加而增加,并呈现假塑性流体特性;在质量浓度为0.2～0.5g/100mL时形成凝胶,凝胶强度受胶体及 Ca2+ 质量浓度的影响明显,同时高酰基结冷胶比例增加,高低复配胶体的凝胶强度减小。并利用红外光谱扫描和核磁共振技术对高酰基结冷胶结构进行初步分析。     

低酰基结冷胶-果胶复配体系的性能

利用质构仪和流变仪对低酰基结冷胶(low acyl gellan,LA)和果胶复配体系的胶体质构和流变性能进行研究。考察不同种类离子(Ca~(2+)、K~+)、离子浓度(0、2、4、6、8、10、20、40 mmol/L)以及LA和果胶不同质量比(100:0、75:25、50:50、25:75)对复配体系质构特性的影响。结果表明,随着离子浓度的增加破坏应力先增大,当达到临界值后开始减小,二价离子(Ca~(2+))的作用效果要强于一价离子(K~+)。复配胶破坏应力随LA比例降低先增加后减少,质量比在75:25时具有显著协同效应。复配体系的黏度随剪切速率增大而减小;当剪切速率相同时,黏度随LA比例的增加而增加,离子种类和浓度对复配体系黏度的影响与质构特性一致。随着温度的升高,复配体系黏度减小,在相同温度条件下,结冷胶与果胶质量比75:25时,体系的黏度最大。储能模量G’大于相应质量比损耗模量G",且G’和G"随LA比例的增加而增大,说明体系的黏性和弹性随LA比例增加而变大。     

Serum release boosts sweetness intensity in gels

This paper describes the effect of serum release on sweetness intensity in mixed whey protein isolate/gellan gum gels. The impact of gellan gum and sugar concentration on microstructure, permeability, serum release and large deformation properties of the gels was determined. With increasing gellan gum concentration the size of the pores present in the protein network, the permeability and the serum release increased, as well as the Young's modulus, the fracture stress and the fracture strain. Increasing the sugar concentration induced an increase of the pore size, but resulted in a decrease of permeability and serum release. The addition of sugar resulted in gels with a higher Young's modulus and a lower fracture strain. This effect was more evident at higher gellan gum concentrations. By changing the protein concentration of the gels, a set of samples was prepared exhibiting constant large deformation properties but varying in serum release and sugar concentration. Serum release significantly boosted sweetness intensity. For example, the sweetness scores for gels with 12% serum release were the same as for gels with 2% serum release but 30% higher sugar concentration. The results indicate that serum release is a tool to compensate for the loss taste intensity related to the reduction of sugar and salt in gelled foods.     

Compressive textural attributes, opacity and syneresis of gels prepared from gellan, agar and their mixtures

Gellan, agar and their mixed gels at an equal proportion of both were subjected to uniaxial compression to determine the textural attributes including fracture characteristics, opacity and syneresis. An increase in concentration of hydrocolloids increased opacity but decreased syneresis. Highly transparent gellan gels with opacity less than 8% were obtained; opacity of agar gels was highest, and was between 5% and 30% for their mixed gels. Syneresis as low as 1.5% was observed with the mixed gel containing 2% each of agar and gellan. The maximum stress and energy for compression increased with the level of gelling agents while instantaneous relaxation in height decreased. Binary combinations or mixed gels containing agar and gellan can provide unique textural and physical characteristics like syneresis and opacity.     

高酰基结冷胶/酪蛋白酸钠复合凝胶粘弹行为的研究

本文研究了酪蛋白酸钠浓度、结冷胶浓度、离子和测试条件对高酰基结冷胶/酪蛋白酸钠复合凝胶粘弹性的影响。结果表明:高酰基结冷胶/酪蛋白酸钠共混体系为典型的切力变稀流体,表观粘度随着酪蛋白酸钠浓度的升高而降低,而随着阳离子浓度的增大出现先增大后减小的变化趋势。压缩速度对复合凝胶硬度几乎无影响,而内聚性和弹性则随着压缩速度的增加而增大。内聚性随着压缩应变的增大出现先增大后减小的变化趋势。复合凝胶的硬度和弹性随着酪蛋白酸钠浓度的增加而下降,但复合凝胶的内聚性对酪蛋白酸钠浓度不敏感。高酰基结冷胶浓度越高,复合凝胶的硬度和弹性越大。相对于一价离子而言,二价离子形成的凝胶更强且用量更少。钾离子的添加对复合凝胶保水性影响较弱,而钙离子的添加则可以提高复合凝胶的保水性。     

TEXTURE PROPERTIES OF GELLAN GELS AS AFFECTED BY TEMPERATURE

Gellan gels can be made very brittle, similar to agar gels, or very flexible, like gelatin gels. The entropy or enthalpy nature governing those gellan gel behaviors was studied by mechanical testing at temperatures varying from 2 to 62C. Both failure stress and strain for 1% low acyl and low acyl/high acyl mixed gellan gels decreased with increasing temperature, indicating that the hydrogen bonding contributed significantly to the stabilization of gellan gels in addition to the polyanion-calcium-polyanion bonding. Hydrophobic interactions were less important. The initial Young's modulus for two mixed high and low acyl gellan gels containing 2 mM Ca⁺⁺ increased with temperature from 2–42C, indicating entropy elasticity. Average molecular weight between adjacent crosslinks for these two mixed gels was larger than 10⁴. For other gels, the entropy elasticity was not a dominant mechanism for elastic force because of molecular weights between crosslinks and from the observation of negative temperature dependence of the modulus.     

Effect of addition of sucrose and aspartame on the compression resistance of hydrocolloids gels

The effect of adding sucrose (5–25% w/w) and aspartame (0.04–0.16% w/w) on the compression resistance of three hydrocolloid gelled systems: κ‐carrageenan, gellan gum and κ‐carrageenan/locust bean gum at three different concentrations (0.3, 0.75 and 1.2% w/w) was studied. Sucrose addition increased true rupture stress in the three‐gelled systems, this effect being stronger in gellan gels. The deformability modulus increased with sucrose concentration in gellan gels, but not in the other systems. Rupture stress and deformability modulus increased with the addition of sucrose only in the harder gels (0.75 and 1.2% w/w). The effect of sucrose addition on the true rupture strain was significant but, in general, not important, mainly for lower gum concentrations. Aspartame addition did not affect the compression parameters.     

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.     

COMPARATIVE STUDY OF LARGE STRAIN METHODS FOR ASSESSING FAILURE CHARACTERISTICS OF SELECTED FOOD GELS

Vane rheometry was compared with uniaxial compression and torsion in evaluating the effects of strain rate on failure shear stress and deformation of soybean protein (tofu) and gellan gum gels. A Haake VT 550 viscotester was used for torsion and vane tests, and compression was performed with an Instron/MTS universal testing machine. Strain or angular deformation at failure was independent of strain rate in the three testing modes. In vane rheometry, failure shear stress increased with increasing low shear rates (< 0.100 s ⁻¹) and was rate independent at higher rates. This strain rate dependency was also evident in compression, varying with the material. For torsion, fracture stress appeared to be rate independent. Shear fracture stresses measured in torsion and compression were in good agreement at strain rates above 0.025 s ⁻¹ and 0.100 s ⁻¹ for tofu and gellan gels, respectively. Shear stresses from the vane method were lower than shear stresses of torsion and compression. Similar texture maps of the food gels studied were generated by plotting stress and strain or angular deformation values of the three testing methods. The findings validate the vane technique as an alternative to torsion and compression for rapid textural characterization of viscoelastic foods.