【作者】 肖茜；

【导师】 童群义；

【作者基本信息】 江南大学 ， 制糖工程， 2012， 博士

【摘要】 本论文以普鲁兰多糖、海藻酸钠及其混合物为研究对象,探究了多糖基可食用膜成膜机理及其与水分子的相互作用,为多糖基可食用膜的工业化生产提供了一定的理论基础。首先研究了普鲁兰多糖、海藻酸钠以及混合多糖溶液在20°C条件下的流变性能。结果表明:海藻酸钠的特性粘度为7.340 dl/g,远高于普鲁兰多糖的特性粘度值。4%的普鲁兰多糖成膜溶液呈现牛顿流体的性质,然而相同浓度的海藻酸钠成膜溶液则为剪切变稀流体。温度对普鲁兰多糖、海藻酸钠以及混合多糖成膜溶液粘度的影响可以通过Arrhenius方程很好的进行拟合。从动态流变试验中看出4%的海藻酸钠以及混合多糖成膜溶液为液态粘弹性溶液,并且将获得的动态粘弹数据使用广义的Maxwell模型进行拟合,得到了离散弛豫谱,从而分析了它们的机械性能。通过Cox-Marz方程对所有样品动态以及稳定剪切粘度的相关性进行了描述,发现该方程可以很好的描述普鲁兰多糖成膜溶液行为。使用流变仪研究普鲁兰多糖、海藻酸钠以及混合样品在干燥成膜过程中多糖分子的构象、链段运动状态变化,发现溶液样品在干燥成膜临界浓度时,普鲁兰多糖分子链段随着体系中水分的蒸发形成了三维穿插缠绕的网络结构,然而海藻酸钠样品则发生了弱凝胶化,形成了三维物理交联网络。同时使用傅里叶红外光谱结合二维相关性分析法研究干燥成膜过程中多糖与水分子之间的氢键作用,得到了普鲁兰多糖膜、海藻酸钠膜以及混合可食用膜体系中水分子的脱除模式。通过制备不同RH条件下的普鲁兰多糖膜、海藻酸钠膜以及混合可食用膜,研究相对湿度对多糖基可食用膜性能的影响。结果发现:在低a_w条件下,增加膜体系中海藻酸钠的含量可以提高膜样品的抗拉强度以及弹性模量,并降低了断裂延伸率;然而随着a_w值的提高相反的变化趋势被观察到。在a_w为0.23-0.43的范围里,水分子对海藻酸钠膜以及混合多糖膜具有反增塑作用。所有样品的水蒸气透过率值随着体系中海藻酸钠含量的增加以及a_w的提高而增大。使用DSC研究了样品的玻璃化转变温度,发现所有样品的玻璃化转变温度随着a_w值的增加而降低,且都只观察到了一个转变温度。使用ATR-FTIR研究了普鲁兰多糖膜、海藻酸钠膜以及混合可食用膜与水分子之间的相互作用。通过使用去卷积、分峰拟合的方法,分析了所有样品在a_w为0.23到0.84范围里红外图谱中O-H的伸缩振动。结果表明:在a_w值为0.84条件下,水分子和普鲁兰多糖膜、海藻酸钠膜以及混合可食用膜之间的氢键作用可以分为四类:分别为非常弱、弱、中等以及强氢键作用;而在a_w值低于0.84条件下,水分子和普鲁兰多糖膜、海藻酸钠膜以及混合可食用膜之间只存在三种不同类型的氢键作用。通过研究不同温度条件下（25、35和45°C）普鲁兰多糖膜、海藻酸钠膜以及混合可食用膜的水分吸附等温线,并结合Clausius-Clapeyron方程计算获得了所有膜样品水分吸附的各种热力学参数。结果表明:当所有膜样品中的水分含量增加到0.1 g/H₂O g dry basis时,净等量吸附热呈降低的趋势;然而随着水分含量的继续增加,所有膜样品的净等量吸附热值都接近于一个常数。通过对微分吸附熵值和焓值作图,得到了所有样品的等动力学温度;结果说明所有膜样品在不同温度条件下对水分的吸附是一个焓驱动的过程。普鲁兰多糖膜、海藻酸钠膜以及混合膜的净积分吸附焓值随着样品中水分含量的增加,先降低到一个最小值,然后快速增加至一个平衡值。更多还原

【Abstract】 In this study, pullulan and sodium alginate were used as film-forming materials. The film-forming mechanism of polysaccharide-based edible films and interaction between water and polysaccharide were investigated.Rheological properties of pullulan, sodium alginate and blend solutions were studied at 20°C, using steady shear and dynamic oscillatory measurements. The intrinsic viscosity of pure sodium alginate solution was 7.340 dl/g, which was much higher than that of pure pullulan. Pure pullulan solution showed Newtonian behavior between 0.1 to 100 s^-1 shear rate range. However, increasing sodium alginate concentration in pullulan-alginate blend solution led to a shear-thinning behavior. The effect of temperature on viscosities of all solutions was well-described by Arrhenius equation. Results from dynamical frequency sweep showed that pure sodium alginate and blend solutions at 4% （w/w） polymer concentration were viscoelastic liquid, whereas the pure pullulan exhibited Newtonian behavior. The mechanical properties of pure sodium alginate and pullulan-alginate mixture were analyzed using the generalized Maxwell model and their relaxation spectra were determined. Correlation between dynamic and steady-shear viscosity was analyzed with the empirical Cox-Merz rule.The change of conformation and chains mobility for pullulan, sodium alginate and blend film forming solutions during drying process were determined by rheometer. With the water content continuously decreasing, the entanglement network was formed by pullulan chains. However, the sodium alginate chains interacted to form physical crosslinking network structure. Moreover, the film-forming mechanism of pullulan, sodium alginate and blend films was studied by ATR-FTIR and 2D correlation spectroscopy.Pullulan-sodium alginate blend films were prepared and characterized as a function of water activity. At low a_w, the incorporation of sodium alginate into pullulan film increased the tensile strength and elastic modulus, but decreased the elongation at break of the composite films; the opposite trends were observed at elevated a_w. Above 0.43 a_w, water exerted a typical plasticization effect upon the biopolymer blends. As a_w increased from 0.23 to 0.43, an anti-plasticization effect was observed as tensile strength and elastic modulus increased. Water vapor permeability （WVP） of all samples increased with the increase of a_w from 0.23 to 0.84,the lowest WVP was detected in pure pullulan films. Moreover, the glass transition temperature （T_g） of all samples decreased substantially with the increase of a_w from 0.23 to 0.84. Within this a_w range, one transition temperature for all the specimens was observed.The stretching vibration band of O-H was investigated using attenuated total reflection Fourier transform infrared spectroscopy, and different water-polysaccharide interactions were identified from 0.23 to 0.84 a_w. At high a_w （0.84）, the hydrogen bonding strength for all samples could be qualitatively assigned as very weak, weak, medium, and strong, respectively. However, three type of hydrogen bonding strength were observed below 0.84 a_w.The moisture sorption isotherms of pullulan, sodium alginate and blend films were determined using a standard gravimetric method at 25, 35 and 45°C. The thermodynamic properties were calculated through direct use of moisture isotherm by applying the Clausisus-Clapeyron equation. Net isosteric heat value for all films decreased with the increase of moisture content to approximately 0.1g/ g H₂O dry basis and then was plateau on axis of moisture content. The plots of differential enthalpy in contrast to entropy provided the isokinetic temperatures for all samples, indicating an enthalpy-controlled sorption process. Net integral entropy for all samples decreased with moisture content to a minimum value but increased thereafter.更多还原