Leslie R B, Carillo P J, Chung T Y, Gilbert S G, Hayakawa K, Marousis S, Saravacos G D, Solberg M
Center for Advanced Food Technology, Cook College/New Jersey Agricultural Experiment Station, Rutgers, State University of New Jersey, New Brunswick 08903.
Adv Exp Med Biol. 1991;302:365-90. doi: 10.1007/978-1-4899-0664-9_21.
The objective of this study was to investigate the influence of structure, and component interactions, on the sorption and transport properties of water in starch-based systems. We compared the effective diffusivity (Deff) of water in two starches, with differing amylose-amylopectin ratios, using either kinetics of water adsorption or analysis of drying curves (water desorption) to estimate Deff. The effect of incorporating small sugar molecules into the granular or gelatinized starch matrices on Deff was measured by drying curve analysis. To investigate the possible mechanisms of water transport, the porosity and microscopic appearance of the samples at different stages of drying were determined. In a complementary study, sorption isotherms and the number of accessible "binding" sites in the starch and starch-sugar systems were determined using gravimetric analysis and inverse gas chromatography (IGC) 'probe analysis'. In the case of the starch-sugar systems, the measurements were made after the components had been 'mechanically mixed', or after more intimate mixing had been achieved by a co-freeze-drying process. The Deff of the starches was found to depend, in a complex way, on the moisture content of the samples. At relatively high moisture contents, the predominant mode of water transport was by liquid diffusion. As the samples became drier, their porosity increased, and the predominant mode of moisture transport was by vapor phase diffusion. As the samples became very dry (less than 10% water content), Deff fell significantly. Incorporation of sugars, in general, led to a reduction of Deff, which was correlated with a corresponding fall in porosity. In agreement with the findings of other workers, for the starches studied, the value of Deff determined from water adsorption measurements was significantly less than Deff determined from water desorption (drying curve analysis). The form of the Deff versus moisture content relationship was, however, independent of the method of measurement (adsorption or desorption). The water sorption and IGC probe analysis results indicated that some physicochemical interaction was expedited by the freeze-drying process. This interaction was manifested by a reduction in water sorption at a given relative vapor pressure, and by major changes in the accessibility of the co-freeze-dried samples to organic probe molecules. Taken together, the results indicate that water transport (diffusion) in starches and in starch-sugar mixtures is dependent significantly on gross structural features (development of porosity during drying), but that specific molecular, physico-chemical interactions must also be considered.
本研究的目的是调查结构和组分相互作用对淀粉基体系中水的吸附和传输特性的影响。我们使用水吸附动力学或干燥曲线分析（水脱附）来估计有效扩散系数（Deff），比较了直链淀粉-支链淀粉比例不同的两种淀粉中水的有效扩散系数。通过干燥曲线分析测量了将小糖分子掺入颗粒状或糊化淀粉基质中对Deff的影响。为了研究水传输的可能机制，测定了干燥不同阶段样品的孔隙率和微观外观。在一项补充研究中，使用重量分析和反相气相色谱（IGC）“探针分析”测定了淀粉和淀粉-糖体系中的吸附等温线以及可及的“结合”位点数量。对于淀粉-糖体系，在组分“机械混合”后或通过共冷冻干燥过程实现更紧密混合后进行测量。发现淀粉的Deff以复杂的方式取决于样品的水分含量。在相对较高的水分含量下，水传输的主要方式是液体扩散。随着样品变干，其孔隙率增加，水分传输的主要方式是气相扩散。当样品变得非常干燥（含水量低于10%）时，Deff显著下降。一般来说，糖的掺入导致Deff降低，这与孔隙率相应下降相关。与其他研究人员的发现一致，对于所研究的淀粉，由水吸附测量确定的Deff值明显小于由水脱附（干燥曲线分析）确定的Deff值。然而，Deff与水分含量关系的形式与测量方法（吸附或脱附）无关。水吸附和IGC探针分析结果表明，冷冻干燥过程加速了一些物理化学相互作用。这种相互作用表现为在给定相对蒸汽压下水吸附减少，以及共冷冻干燥样品对有机探针分子的可及性发生重大变化。综合来看，结果表明淀粉和淀粉-糖混合物中的水传输（扩散）显著取决于总体结构特征（干燥过程中孔隙率的发展），但也必须考虑特定的分子物理化学相互作用。
