影响果胶钙凝胶形成的因素以及果胶钙凝胶应用

果胶钙凝胶具有化学性质稳定、生物相容性好、食用安全等优点,在食品、药品、微生物等领域具有潜在应用价值。文中综述了果胶钙凝胶的形态、结构、安全性,影响其形成因素、应用现状与发展趋势,以期为果胶钙的应用提供理论指导。     

Effect of complexation of oxidised corn starch with mineral elements on physicochemical properties

The objective of this study was to determine the effect of complexation of oxidised starch with mineral elements on its physicochemical properties. Corn starch was oxidised with sodium hypochlorite and, afterwards, modified with ions of potassium, magnesium and iron. Thus, native and modified starches were analysed for: contents of mineral elements, colour parameters (L*a*b*), water binding capacity and solubility in water at temperature of 60 and 80 °C. Thermodynamic characteristics of gelatinisation by DSC, molecular weight distribution by GPC, intrinsic viscosity and pasting properties by RVA were studied. The efficiency of incorporation of metal ions into oxidised corn starch was about 30%, 20% and 20% for potassium, magnesium and iron ions, respectively. The complexation with potassium ions caused the greatest changes in the molecular weight distribution and the intrinsic viscosity of starches and viscosity of starch pastes. Only modification of starch with iron ions affected the colour parameters of the starch. Incorporation of metal ions into starch resulted also in changes in its water binding capacity and solubility in water.     

Microstructure and elastic modulus of mixed gels of gelatin + oxidized starch: Effect of pH

The microstructure and elastic shear modulus of cold-set gels formed from high-sugar aqueous mixtures of gelatin (7 wt%) + oxidized starch (0-6 wt%) were investigated as a function of pH. Samples prepared at 90 °C, with citric acid added to adjust the pH, were rapidly quenched to ∼1 °C, subjected to a standard thermal treatment (40 °C for 10 min), and then investigated by confocal microscopy and small-deformation rheology at 24 °C. Under ‘natural’ conditions of pH ≈ 5.2 (no citric acid addition), the samples exhibited phase separation with a characteristic spinodal-type morphology. The spatial extent of the structural heterogeneity, expressed by a single length-scale parameter, was found to increase with starch concentration. Gradual acidification led to a reduction in this length-scale parameter, leading to complete inhibition of phase separation below a certain characteristic pH value in the range 4.5-4.9 (depending on starch content). Over the investigated pH range, the effect of starch addition was to reduce the storage modulus of the resulting gel. This reduction was more pronounced for the phase-separated samples. The pH of maximum rigidity was found to decrease from pH_max ≈ 4.6 for 0 wt% starch to pH_max ≈ 4.2 for 6 wt% starch. Taken all together, these observations can be understood in terms of the effects of pH on the cross-linking behaviour of the gelatin and the nature of the gelatin-starch electrostatic interactions. The microscopy results are consistent with a transition in behaviour from thermodynamic incompatibility (segregative interactions) at high pH to soluble complexation (associative interactions) at low pH.     

柠檬黄素在淀粉凝胶内的扩散特性研究

测定了在4℃和35℃条件下柠檬黄素在3种浓度的小麦﹑小米淀粉凝胶内的扩散系数。结果表明,在相同条件下,与小麦淀粉凝胶相比,柠檬黄在小米淀粉凝胶内的扩散较慢。扩散系数随着凝胶浓度的减小而增大,随着温度升高而升高。与改变浓度相比,降低温度更能有效地降低柠檬黄在淀粉凝胶内的扩散速度。     

Development of oxidised and heat-moisture treated potato starch film

This study investigated the effects of sodium hypochlorite oxidation and a heat-moisture treatment of potato starch on the physicochemical, pasting and textural properties of potato starches in addition to the water vapour permeability (WVP) and mechanical properties of potato starch films produced from these starches. The carbonyl contents, carboxyl contents, swelling power, solubility, pasting properties and gel texture of the native, oxidised and heat-moisture treated (HMT) starches were evaluated. The films made of native, oxidised and HMT starches were characterised by thickness, water solubility, colour, opacity, mechanical properties and WVP. The oxidised and HMT starches had lower viscosity and swelling power compared to the native starch. The films produced from oxidised potato starch had decreased solubility, elongation and WVP values in addition to increased tensile strength compared to the native starch films. The HMT starch increased the tensile strength and WVP of the starch films compared to the native starch.     

Pasting and rheologic properties of potato starch and maize starch mixtures

This study characterized the pasting and rheologic behavior of potato/maize starch mixtures of various ratios. Pasting analysis using a Brabender Viscograph indicated that most important pasting parameters did not show a linear change that reflected the ratio of starches. A significant effect on final viscosities and setback was evident. The diameter distribution of starch granules that were heated to 70°C was determined by a laser particle size analyzer. The result suggested that the swelling of starch granules in the mixtures was reduced at the onset of gelatinization. Measurement of dynamic viscoelasticity measurement demonstrated that the mixtures showed slightly higher loss modulus than those seen for the control at small measuring frequencies. The mixture pastes with a high proportion of potato starch exhibited more pseudoplasticity and had a more significant thickening effect than either control paste. Nonadditive behavior was found by mixing potato and maize starch. This suggests that an appropriate blend of starches from diverse botanical origins may provide a simple practical avenue for manipulation.     

Effect of cross-linking on the resistance to enzymatic hydrolysis of waxy maize starch and low-methoxy pectin

Gelatinised waxy maize starch and low-methoxy pectin mixtures were solubilised/dispersed in water and cross-linked with sodium trimetaphosphate (STMP). The polysaccharides were subjected to α-amylase, β-amylase or amyloglucosidase (AMG) hydrolysis for different times, and at two starch to pectin combination ratios (3:2 and 2:3). The extent of hydrolysis by porcine pancreatic α-amylase of the cross-linked (gelatinised) starch was 54.8–58.9% in comparison with gelatinised starch (for different incubation times), corresponding to 52.3–58.9% and 51.3–55.3% of the starch in the uncross-linked (UL) 3:2 and 2:3 starch to pectin ratios (for the same hydrolysis times). Blends of individually cross-linked starch to pectin ratios (3:2 and 2:3) were hydrolysed to 66.2–67.0% and 65.4–71.8%, respectively, compared with the corresponding UL counterparts. When the gelatinised starch was incubated for 0.5–36 h with β-amylase, hydrolysis ranged from 9.2% to 26.2%, and from 5.4% to 12.2% when the starch was cross-linked (corresponding to 40.0–58.7% of the gelatinised starch). For starch to pectin ratios of 3:2 or 2:3 blended after cross-linking, or by simultaneous cross-linking, hydrolysis represented 2.3–3.4% and 0.3–0.6% for the 3:2 ratio but only 1.2–2.0% and 0–0.3% for the 2:3 ratio. Hydrolysis with AMG using a 0.1 mg ml⁻¹ enzyme concentration caused 51.8% hydrolysis of gelatinised starch, which was lowered to 35.2% (i.e. by 68%) after cross-linking. At a higher enzyme concentration (1 mg ml⁻¹), the comparable figures were 91.7% and 71.9% (a reduction of 78.4%). For the UL 3:2 starch to pectin ratio and 0.1 and 1 mg ml⁻¹ enzyme concentrations, there was 27.8% and 56.5% hydrolysis of the polysaccharide which translated to 24.3% (87.4%) and 45.8% (81.1%), respectively, after cross-linking. Comparable figures for the 2:3 ratio (for the 0.1 and 1 mg ml⁻¹ enzyme concentrations) were 20.2% and 36.5% hydrolysis of the UL samples and 18.2% (90.1%) and 32.5% (89.0%) hydrolysis, respectively, after cross-linking.     

亚麻籽胶对糯米淀粉凝胶冻融稳定性影响

为了解亚麻籽胶对糯米淀粉凝胶冻融稳定性的影响,利用差示扫描量热仪、X-射线衍射、傅里叶变换红外光谱仪和扫描电镜测定添加不同比例亚麻籽胶的糯米淀粉凝胶经过7次冻融循环后的热力学特性、结晶性、分子结构和微观结构。结果显示,亚麻籽胶能显著降低糯米淀粉凝胶的析水率;淀粉凝胶熔融焓/糊化焓降低显示糯米淀粉凝胶老化受抑制;随着亚麻籽胶添加量增大糯米淀粉凝胶相对结晶度降低,显示亚麻籽胶抑制了淀粉凝胶的重结晶;亚麻籽胶使淀粉凝胶羟基伸缩振动峰发生较大的位移,增强分子间氢键作用力,而没有生成新的基团;添加亚麻籽胶的淀粉凝胶微观结构表面光滑平整,凹洞较小,基质较紧密。说明亚麻籽胶能提高糯米淀粉凝胶的冻融稳定性。     

Isomaltodextrin strengthens model starch gels and moderately promotes starch retrogradation

Isomaltodextrin (IMD) is a novel highly branched α-glucan with emerging applications in foods due to its nutritional functionalities. In this study, the impact of IMD on the viscoelasticity and microstructure of starch gels and starch retrogradation were investigated. IMD solutions displayed typical Newtonian behaviour. Their viscosities had a positive correlation with concentration and a negative correlation with temperature. When maintained at relative humidity of 95%, IMD absorbed 40% water of its original weight. The addition of IMD to normal corn starch increased strength of gels as indicated by higher storage moduli (G′) and resulted in a denser and smaller pore structure, but there were no changes in elasticity. Upon storage for 7 days, addition of IMD at high concentration (starch: IMD = 2:1) significantly increased the degree of starch retrogradation. This study provided perspectives underlying applications of IMD in starchy foods as a novel ingredient with textural functionality.     

Conformational ordering and gelation of gelatin in mixtures with soluble polysaccharides

Previous studies have shown that conformationally disordered, soluble biopolymers cause large enhancements in self-association of calcium pectinate, thermally denatured whey protein and gelling maltodextrin under conditions where the pre-gel solutions remained as a single phase. The purpose of the present work was to screen for similar enhancements in gel strength and rate of conformational ordering of gelatin on incorporation of soluble, disordered polysaccharides. Type B gelatin was used at a fixed concentration of 5.0 wt%, at a pH well above its isoelectric point of ∼4.5. Mixtures were prepared at 45 °C, where the gelatin is in the disordered coil form. Gel strength was characterised as Young's modulus (E), derived from the initial slope of compression curves for gels formed by holding for 16 h at 5 °C. Rate of conformational ordering of gelatin (triple-helix formation) was monitored by changes in optical rotation during and after rapid quenching from 45 to 5 °C. The polysaccharides studied were carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), guar gum, gum arabic, dextran and inulin, all of which were used in compression testing. Combinations of gelatin with HPMC and guar gum became immediately turbid on mixing and could not, therefore, be included in the samples characterised by optical rotation. The other mixtures remained homogeneous (i.e. single-phase) on holding at 45 °C. The results obtained were entirely negative. Incorporation of the soluble polysaccharides caused no significant changes in Young's modulus, and optical rotation values remained within ∼10% of those for gelatin alone. It is suggested that the enthalpic advantage of segregation is sufficient to overcome the small reduction in entropy from association of conformationally immobile subunits in gelation of calcium pectinate, whey protein and maltodextrin, but not sufficient to overcome the much greater loss of entropy from conversion of flexible gelatin coils to rigid triple helices.     

Associative and segregative interactions between gelatin and low-methoxy pectin: Part 2—co-gelation in the presence of Ca

The effect of segregative interactions with gelatin (type B; pI=4.9; 0–10 wt%) on the networks formed by low-methoxy pectin on cooling in the presence of stoichiometric Ca²⁺ at pH 3.9 has been investigated by rheological measurements under low-amplitude oscillatory shear. Samples were prepared and loaded at 85 °C, cooled (1 °C/min) to 5 °C, held for 100 min, and re-heated (1 °C/min) to 85 °C, with measurement of storage and loss moduli (G′ and G″) at 10 rad s⁻¹ and 2% strain. The final values of G′ at 5 °C for mixtures prepared at the same pH without Ca²⁺ were virtually identical to those observed for the same concentrations (0.5–10.0 wt%) of gelatin alone, consistent with the conclusion from the preceding paper that electrostatic (associative) interactions between the two polymers become significant only at pH values below 3.9. Increases in moduli on cooling in the presence of Ca²⁺ occurred in two discrete steps, the first coincident with gelation of calcium pectinate alone and the second with gelation of gelatin. Both processes were fully reversible on heating, but displaced to higher temperature (by 10 °C), as was also observed for the individual components. The magnitude of the changes occurring over the temperature range of the gelatin sol–gel and gel–sol transitions demonstrates that the gelatin component forms a continuous network; survival of gel structure after completion of gelatin melting shows that the calcium pectinate network is also continuous (i.e. that the co-gel is bicontinuous). On progressive incorporation of NaCl (to induce phase separation before, or during, pectin gelation) the second melting process, coincident with loss of calcium pectinate gel structure, was progressively abolished, indicating conversion to a gelatin-continuous network with dispersed particles of calcium pectinate. These qualitative conclusions are supported by quantitative analyses reported in the following paper.     

Rheological behaviour of uncross-linked and cross-linked gelatinised waxy maize starch with pectin gels

Rheological characterisation of uncross-linked (UPS) and cross-linked (CPS) waxy maize starch with pectin was conducted to determine the influence of pectin on the properties of the starch. The viscoelastic behaviour of 5% (w/v) gel systems containing UPS and CPS polysaccharides at 25 °C was evaluated by small angle deformation oscillation rheometry. Viscoelasticity measurements of the cross-linked polysaccharides indicated that the elastic component increased after cross-linking. Among all gels studied, the properties of the CPS mixtures (ratios 2:3 and 3:2) showed quite high storage (G′) and loss (G″) moduli (compared with gels of other ratios), indicating that gels of these two particular ratios had the greatest degree of elasticity and were very well structured. The results suggest that cross-linking between starch and pectin molecules can give rise to novel rheological properties.     

Effect of gluten content on recrystallisation kinetics and water mobility in wheat starch gels

The effect of gluten on starch retrogradation at 5 °C was studied using ¹H NMR relaxometry. Gels were made from gluten and starch at 27.8 and 38.5% total solids and with gluten comprising either 10, 15 or 20% of the solids. Changes in the transverse relaxation time constant (T₂) were related to water mobility. Mono‐exponential analysis of relaxation curves showed that, in general, gluten retarded starch retrogradation. T₂ values in gluten gels also decreased during storage, but to a much lesser extent. Distributed exponential analysis showed that two distinct regions of T₂ were observed in all samples. During aging, the peak values of both regions shifted to lower values for all gels. Starch gel samples showed the most significant shift, and gluten gels showed the least. The three levels of gluten addition in starch/gluten gels produced similar shifts. For all samples the signal intensity of the less mobile region decreased more dramatically than that of the more mobile region during storage. It was suggested that gluten retards water loss in the granule remnants. Copyright © 2004 Society of Chemical Industry     

Associative and segregative interactions between gelatin and low-methoxy pectin. Part 3. Quantitative analysis of co-gel moduli

The experimental moduli (G′ at 5 °C) reported in the preceding paper for gelatin–calcium pectinate co-gels (pH 3.9; 1.0 wt% pectin; stoichiometric Ca²⁺; 0–10 wt% gelatin) formed in the presence or absence of 1 M NaCl have been analysed using a single adjustable parameter, p, to characterise partition of solvent. The analysis of samples incorporating 1 M NaCl assumed complete segregation of calcium pectinate into dispersed particles in a continuous gelatin matrix, with p defined as the ratio of water/polymer in the gelatin phase divided by the corresponding ratio for the pectin phase. Relative phase volumes at each trial value of p were used to determine the polymer concentration in each phase, and the corresponding moduli were obtained from standard calibration curves. For solvent distributions where the calculated modulus of the continuous gelatin phase was higher than that of the dispersed calcium pectinate phase, co-gel moduli were derived using the Takayanagi isostrain model, and the isostress model was used for the converse situation. The p factors required to give perfect agreement with the moduli observed experimentally were tightly grouped around a single value (p=1.21) for all concentrations of gelatin studied, indicating that the assumption of complete segregation is reasonably valid. Calculated moduli for the gelatin phase were in good agreement with experimental values obtained by melting the gelatin network, centrifuging to sediment the dispersed calcium pectinate particles, and re-gelling the gelatin supernatant. The same p factor (1.21) was used to derive calculated moduli for co-gels formed in the absence of NaCl, where the mixed solutions remain monophasic, by application of the relationship proposed by Davies for bicontinuous composites. The modulus of the calcium pectinate gel, which is already present when the gelatin network forms, was calculated (i) on the assumption of dynamic cross-linking (i.e. using the concentration-dependence of G′ for calcium pectinate alone), and (ii) for permanent cross-linking (by application of deswelling theory). The experimental moduli moved from close agreement with the former model to close agreement with the latter as the gelatin concentration increased from 0 to 10 wt%, consistent with a progressive increase in the extent of rearrangement of the calcium pectinate network required to accommodate the compression introduced by gelation of gelatin.     

Phenomenological viscoelasticity of some rice starch gels

The applicability of a powerful but still easy to use technique, based on a phenomenological theory of viscoelasticity, for processing and analyzing dynamic mechanical data of some rice gels was investigated. Based on this theory a continuous relaxation spectra was generated by application of Tikhonov regularization procedure on continuous Maxwell model. Interpretation of relaxation spectra in terms of number of peaks, its peak intensity H(λ) and appearance of its main distribution peak and magnitude of equilibrium elasticity modulus (G_e) of continuous Maxwell model was found to appropriately reflect main peculiarities of the viscoelastic behavior of rice starch gels. An increase in number of peaks in the relaxation spectra was observed for starch gels having higher amylose content indicating the creation of more heterogeneous structure. H(λ) and G_e values also increased with increase in amylose content demonstrating a transition of the system to more stable state like a gel.     

7种淀粉凝胶应力松弛特性研究

将7种淀粉采用相同方法制备出凝胶块作为实验试样,经质构仪进行压缩和应力松弛实验得到流变学特性参数。利用统计分析软件进行非线性回归拟合,建立了广义Maxwell力学模型。结果表明:淀粉凝胶具有良好的压缩黏弹性力学性质,五元件广义Maxwell模型适用于模拟淀粉凝胶的应力松弛现象。通过主成分分析,应力松弛参数可归纳为两类,即凝胶粘弹特性和凝胶松弛时间。      

Effect of damaged starch on wheat starch thermal behavior

The influence of damaged starch (DS) on gelatinization and retrogradation wheat starch properties was investigated. Samples with different content of DS were obtained and evaluated. DSC was used for monitoring the changes in thermal behavior of the starch samples at different water amounts. Starch thermal transitions were affected simultaneously by DS content and water content. The Flory–Huggins parameters were modified by DS. A significant raise in the T°_m, and x_1–2, and a decrease in ΔH_u was recorded. The AP retrogradation kinetics was evaluated by Avrami model. A significant increase of the AP crystallization rate was observed when DS increased. The results demonstrated the importance of the presence of physically damaged granules on wheat starch properties.     

海藻酸钠与钙离子对大米淀粉糊化的影响

为了探究海藻酸钠与钙离子对大米淀粉糊化的影响,分别采用快速黏度分析仪和流变仪测定了大米淀粉在海藻酸钠和钙离子存在下的成糊特性与淀粉糊状态,并用扫描电子显微镜观察了大米淀粉的糊化显微结构。结果表明,钙离子对大米淀粉的成糊特性无显著性影响;海藻酸钠将体系黏度提高了135%,并使大米淀粉糊呈现似液状态(tanδ1);在体系水分蒸发脱离的条件下,海藻酸钠与钙离子形成了网状凝胶结构,并使大米淀粉糊呈现稳定的似固状态(tanδ1)。因此,海藻酸钠与钙离子能够在大米淀粉糊化过程中形成浓缩诱导型胶凝,从而使大米淀粉糊的结构状态相对固定化。