结冷胶凝胶特性及在食品工业中的应用

目的:介绍新型微生物多糖--结冷胶的凝胶特性及其在食品工业中的应用现状和前景.方法:查阅今年来国内外的相关文献报道,并进行分析、整理和归纳.结果:结冷胶组织相容性和复配性能良好,具有良好的透明性,凝胶性能卓越,具有独特的胶凝和融化温度,可形成多种凝胶质构,在极低的用量下形成的预(弱)凝胶可以发挥良好的悬浮、稳定作用.结论:结冷胶作为一种新型凝胶剂,其优异的性能将在食品工业中得到广泛应用.     

Effect of expansion by instantaneous controlled pressure drop on dielectric properties of fruits and vegetables

The instantaneous controlled pressure drop (DIC) treatment is used for creation of a porous structure during drying of fruits and vegetables. DIC is based on high temperature, short time heating followed by an abrupt pressure drop into a vacuum. This abrupt pressure drop provokes auto-vaporization of the superheated liquid, expansion and breaking of the cell walls and instantaneous cooling. This process step is inserted between two drying stages at a moisture content of about 20% wet basis. The use of microwave radiation would provide more rapid and homogeneous heating than using steam in the DIC treatment and hot air during the final stage of drying. For that purpose the dielectric properties of the raw and DIC treated products were measured. The measurements were carried out with an open-ended coaxial probe at a frequency of 915 MHz in the range of temperatures 20-90 °C and moisture content 5-80% w.b. Three regions were revealed for the dependences of the dielectric constant and loss factor on moisture content. At low moisture content, these properties increased linearly with moisture content. At the middle moisture content, the increase was also linear but much steeper. At high moisture content, the dielectric properties were constant. The limits of these regions were different for ε′ and ε″ as well as for the products. The dielectric properties were slightly temperature dependent. The penetration depth increased with decreasing moisture content. The DIC treated products exhibited slightly lower dielectric properties than the raw products.     

离子对结冷胶凝胶温度及强度的影响

主要研究了不同浓度的钙、镁、钾、钠离子对结冷胶凝胶温度及强度的影响;不同浓度的结冷胶与离子对凝胶强度的影响;当钙、镁、钾、钠离子含量一定时,不同浓度的结冷胶对凝胶温度及强度的影响;钙离子和钾、钠离子对结冷胶凝胶是否有协同作用。结果表明,随着离子浓度的增加,凝胶温度先升高后降低,凝胶强度先增大后减小,在离子含量很少或很多时,结冷胶的凝胶温度和强度都很低。凝胶强度和温度随着结冷胶浓度的增加而增加。钙离子和钾、钠离子在促进结冷胶凝胶上无协同作用。     

Rheological analysis of emulsion-filled gels based on high acyl gellan gum

Emulsion-filled gels are widely used in cosmetic, food, and pharmaceutical industry. As rheological properties of these systems are strongly dependent on the properties of the gelled polymer network, rheological characteristics of gels containing high and low acyl gellan gum were analyzed. Under the processing conditions low acyl emulsions were unstable, thus in the present work the influence of oil and hydrocolloid concentrations on the viscoelastic behavior of emulsion-filled gels containing high acyl gellan gum was studied. Increasing gellan concentration (from 0.1 g/100 g to 0.5 g/100 g) produced stronger gels, while oil fraction (10 g/100 g–30 g/100 g) slightly affected the elastic behavior of the emulsions reinforcing the structure and the elastic characteristics of the gellan matrix. Sauter diameter (d₃₂) was measured for all emulsions and an average value of 12 μm was obtained. Rheological data (oscillatory and creep–recovery tests) were successfully modeled to interpret the structural characteristics of the gelled emulsions. The broadened Baumgaertel–Schausberger–Winter spectrum was used to represent the linear viscoelastic behavior of the continuous phase and the emulsified system, showing that the rheological behavior of the systems was controlled by the highly structured continuous phase rather than the contribution of filler lipid droplet in the emulsion. Relaxation spectra were validated using creep–recovery experiments. Regardless of hydrocolloid concentration, creep compliance of the gel emulsions decreased compared with their respective gels, showing that the inclusion of oil droplets produced a reinforcement of the structure and the gel strength of the matrix.     

Sol-gel transition temperatures of high acyl gellan with monovalent and divalent cations from rheological measurements

The sol–gel transition temperatures of 0.1–1.0% high acyl gellan (HAG) with 0–200 mM NaCl or KCl and 0–20 mM CaCl₂ or MgCl₂ were determined using rheological measurements. Transition temperatures for monovalent cations, Na⁺ and K⁺, in the range of 50–80 °C were not significantly different (p > 0.5). Absence of thermal hysteresis was the salient feature. However, thermal hysteresis (∼4.4 °C) was observed for 0.1% HAG without added salt, but disappeared on increasing HAG and counterion concentrations. Few concentrations of HAG and added monovalent and divalent cations showed thermal hysteresis not higher than 2.5 °C. Transition temperatures for divalent cations were similar to those for monovalent cations although for considerably lower concentrations of Ca²⁺ or Mg²⁺. Increasing concentrations of monovalent and divalent counterions give rise to higher transition temperatures but not to higher storage moduli. This was interpreted as a lack of cross-link formation in the three-dimensional network structure of the gels. A single sol–gel transition diagram for monovalent cations is proposed, in which different zones associated with the presence of ordered and disordered conformations serve to identify the conditions in which HAG can exist in aqueous media.     

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.     

Effect of inulin on texture and clarity of gellan gels

The effect of inulin on the gelation of 0.5 wt% low acyl gellan in the presence of increasing concentrations of potassium chloride was investigated by large deformation compression experiments and visible light absorbance. The sugar and salt concentrations varied from 0 to 15 wt% and 40-100 mM, respectively. Stress and strain at failure along with Young’s modulus were calculated from each compression curve. Samples prior to compression were refrigerated at 5 °C for 24 h. Reduced gel strength and firmness were observed for all inulin and salt concentrations. Increasing amounts of inulin resulted in an increase in gel strength which was greater for higher potassium concentrations. Elasticity values did not exhibit great diversion. Inulin at concentrations of 5 and 10 wt% led to less turbid gels than those with only gellan. Samples containing 15 wt% inulin gave absorbance readings greater than 1.     

乳清浓缩蛋白WPC80凝胶工艺确定及其凝胶特性分析

以乳清浓缩蛋白(WPC80)为研究对象,分析了温度、时间、料液浓度、钙离子强度、乳糖浓度及pH值对其凝胶的影响,并通过测试样品凝胶特性。确定了WPC80凝胶的最佳工艺条件:配置质量分数为9%的WPC80溶液,室温400 r/min搅拌30 min至样品全部溶解;4℃储存10 h以上,便于蛋白溶解及水合;添加质量分数为0.12%的氯化钙;65℃,转速为80 r/min恒温水浴30 min;调节样品pH值为5.5;85℃水浴静置20 min形成凝胶。     

Gelation and microstructure of dilute gellan solutions with calcium ions

The viscoelasticity at 25 °C and microstructure of 0.02–0.07 wt% of low acyl gellan aqueous media were investigated for ratios of Ca²⁺ to gellan in the range of 0–38.8, using small amplitude oscillatory shear rheometry and confocal laser scanning microscopy (CLSM), respectively. The total ionic concentration (C_T = γ C_P + C_S, being C_P and C_S the gellan and calcium concentrations, respectively, and γ the mean activity coefficient) of the systems was found to be the triggering and critical factor for the gelation and elasticity of gellan systems. The gel point (T_gel) and storage moduli (G′) increased upon increasing C_T. However, G′ showed a maximum for C_T = 9.3 ± 1.2 meq/L, followed by a progressive reduction as C_T increased; this was primarily due to further addition of calcium, as C_P had a low contribution to C_T of the systems. CLSM demonstrated that the level of counter-ions was enough to induce the formation of a network, whose connection depended on C_P and whose reinforcement was ion dependent. Therefore, even at very low levels of gellan, it is possible to create a wide spectrum of viscoelastic behaviors going from structured liquids to strong gels through the specific combinations of gellan and cation concentrations.     

Stress relaxation behaviour of high acyl gellan gels

Stress relaxation behaviour of high acyl gellan gels has been investigated, and data were fitted successfully by a seven elements empirical model and a four term modified Maxwell model with three fixed relaxation times (20, 200 and 2000 s). In addition, the effect of testing parameters on stress relaxation characteristics and the relationship between those characteristics and intrinsic gel properties were studied. High acyl gellan gels were tested in stress relaxation with different cross‐head speeds (0.1–10 mm s^?1) to applied strains (3–30%). The results showed that the cross‐head speed had little effect on stress relaxation behaviour of gels. With increasing the applied strain, the initial stress and the equilibrium stress increased. The equilibrium stresses from relaxation measurement were positively related to the hardness from TPA tests (R² = 0.991). Relaxation appeared to be associated with the shifting of cross‐links in the gel matrix.     

乳成分对酸奶凝胶微观结构和流变学性质的影响

酸奶凝胶的许多宏观的物理特性与其微观结构和流变学性质密切相关。从酸奶的微结构、流变学性质和质地等方面综述了乳脂肪、蛋白质及调节酪蛋白和乳清蛋白比例对酸奶凝胶的影响。     

频率和温度对鲍鱼介电特性的影响

采用同轴探针方法分别测定了20～120℃,频率300～3000MHz内鲍鱼的介电常数和介电损失。温度一定时,鲍鱼的介电常数和介电损失均随频率的升高而减小。频率一定时,介电常数随温度升高,先增大后减小,介电损失随温度的升高而增大。本研究提出了在915、2450MHz下,介电常数和介电损失随温度变化的预测方程,预测值与实验值有较好的一致性。在915、2450MHz下,鲍鱼的穿透深度均随着温度的升高而减小。     

脱脂乳的不同热处理对其酸奶凝胶流变学性质的影响

研究了复原脱脂乳经不同加热处理后其酸奶凝胶形成过程中流变学特性的变化,复原脱脂乳经７０～９０℃处理１０～２５ｍｉｎ,用Ｄ－葡萄糖－δ－内酯酸化成胶,用流变学方法动态监测凝胶性能。并监测酸化过程和成胶时间,结果显示,不同条件下自理后的脱脂乳在酸化过程中,ｐＨ值并未改变,但产储存模量（Ｇ′）和损失模量（Ｇ″）随受质变程度的增加而增加,只是当加热温度为９０℃时反而随加热时间的延长而降低,在８５℃加热２５     

Rheology-structure properties of waxy maize starch–gellan mixtures

Dynamic oscillatory shear and confocal laser scanning microscopy were used, respectively, to study the viscoelastic properties and ultrastructure of mixtures of unmodified waxy maize starch (3%) and gellan (0.005–0.05%), pasted at 75 and 90 °C. The two temperatures resulted in different rheological properties and ultrastructure. At 75 °C swollen and partially disrupted granules were observed, while at 90 °C the dominant feature was the presence of granule remnants. Addition of gellan produced mixtures with different elastic properties depending on the extent of granular disruption and gellan concentration in the mixture. Below 0.02% gellan, swollen and disrupted starch granules were surrounded by compact, yet slightly interconnected, gellan networks resulting in enhanced blends at both temperatures. Above such gellan concentration no enhancement was observed and gellan dominated the viscoelastic behavior of the mixtures because of the existence of more evenly distributed networks with swollen or disrupted starch granules exerting a weakening effect on the resulting structure.     

结冷胶对低脂低盐牛肉凝胶品质的影响

研究了结冷胶(GG)对低脂低盐牛肉凝胶蒸煮损失(CL)、保水性(WHC)、色泽及质构的影响.试验研究结果表明:(1)GG的添加可显著降低牛肉糜的CL;(2)GC的添加可极显著降低牛肉凝胶WHC;(3)GG的添加对牛肉凝胶色泽无显著影响;(4)GG极显著地降低牛肉凝胶的硬度和咀嚼性.     

高酰基结冷胶特性及应用研究进展

目的:介绍新型微生物多糖-高酰基结冷胶的研究进展和前景.方法查阅近年来国内外的相关文献报道,并进行分析、整理和归纳.结果 胶体浓度、外加金属阳离子类型和含量、pH值、糖份都会对凝胶特性和流变性产生影响. 结论 高酰基结冷胶作为一种新型凝胶剂,只有在充分理解掌握其凝胶特性的基础上才能获得理想的效果.     

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(HA)特性的研究进展

高酰基结冷胶是美国Kelco公司开发的一种新型微生物多糖,它是由少动鞘脂单胞菌（Sphingomonas paucimobilis）经有氧发酵产生的。高酰基结冷胶是集凝胶剂、稳定剂、悬浮剂于一身的多功能亲水性胶体,具有热可逆性、高持水性、良好的复配性等优良特性,因此在食品工业中逐步展现广阔的应用前景。本文综述了高酰基结冷胶的结构、凝胶机理及其特性,并对其应用前景作了探讨。     

Using whey protein gel as a model food to study dielectric heating properties of salmon (Oncorhynchus gorbuscha) fillets

It is desirable to develop rapid commercial microwave and radio frequency sterilization processes to produce high quality shelf stable muscle foods, particularly aquatic foods. Whey protein gels containing d-ribose and salt were studied as a model food to determine heating patterns in salmon fillets during high temperature microwave sterilization processes. Dielectric constant (?′) and loss factor (?″) of whey protein gels with d-ribose (0.5 g/100 g, 1 g/100 g, and 1.5 g/100 g) at different salt contents (0, 0.1 g/100 g, 0.2 g/100 g, 0.3 g/100 g, 0.4 g/100 g, and 0.5 g/100 g) and frozen and thawed pink salmon (Oncorhynchus gorbuscha) fillets were determined over the frequency range of 27-1800 MHz at temperatures ranging from 20 to 120 °C. The dielectric properties of whey protein gels containing 1 g/100 g d-ribose and 0.2 g/100 g or 0.3 g/100 g salt closely matched the dielectric behavior of salmon fillets in both radio frequency (RF, 27 MHz) and microwave (MW, 915-1800 MHz) ranges. Altering the salt content had a greater impact on dielectric constant and loss factors at lower frequencies. These results suggest that whey protein gel may be a good model food for microwave sterilization process development, particularly for determining the locations of cold and hot spots in complex muscle foods.     

Evaluating banana ripening status from measuring dielectric properties

Electrical properties of banana fruit were studied in order to develop a rapid and non-destructive assessment method and to control its ripening treatment. A 5 V sine wave AC power supply and a rectangular parallel plate capacitor sample were used to span the difference in capacitance caused by the introduction of a banana fruit between the plates. To remove the effect of air gap between the plates, an equivalent capacitor was derived. The correlation between dielectric constant and quality parameters of banana fruit was investigated. The dielectric constant of banana fruit decreased as a result of the ripening treatment. Experiments indicated that the best frequency of sine wave that can predict the level of ripeness was 100 kHz. The coefficient of determination (R²) of ripeness level prediction was obtained 0.94 at this frequency. This method can confidently predict the ripeness level of banana fruit.