Department of Chemical and Bioprocesses Engineering, Pontificia Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Macul, Santiago, Chile.
Carbohydr Polym. 2012 Oct 1;90(2):1147-58. doi: 10.1016/j.carbpol.2012.06.066. Epub 2012 Jul 2.
The initial characteristics of emulsions and the rearrangement of the oil droplets in the film matrix during film drying, which defines its microstructure, has an important role in the physical properties of the emulsion-based films. The objective of this work was to study the effect of the microstructure (two droplet size distributions) and stability (with or without surfactant) of HPMC oil-in-water emulsions over physical properties of HPMC emulsion-based edible films. HPMC was used to prepare sunflower oil-in-water emulsions containing 0.3 or 1.0% (w/w) of oil with or without SDS, as surfactant, using an ultrasonic homogenizer. Microstructure, rheological properties and stability of emulsions (creaming) were measured. In addition, microstructure, coalescence of oil droplets, surface free energy, optical and mechanical properties and water vapor transfer of HPMC films were evaluated. Image analysis did not show differences among droplet size distributions of emulsions prepared at different oil contents; however, by using SDS the droplet size distributions were shifted to lower values. Volume mean diameters were 3.79 and 3.77 μm for emulsions containing 0.3 and 1.0% without surfactant, respectively, and 2.72 and 2.71 μm for emulsions with SDS. Emulsions formulated with 1.0% of oil presented higher stability, with almost no change during 5 and 3 days of storage, for emulsions with and without SDS, respectively. Internal and surface microstructure of emulsion-based films was influenced by the degree of coalescence and creaming of the oil droplets. No effect of microstructure over the surface free energy of films was found. The incorporation of oil impaired the optical properties of films due to light scattering of light. Addition of oil and SDS decreased the stress at break of the emulsion-based films. The replace of HPMC by oil and SDS produce a lower "amount" of network structure in the films, leading to a weakening of their structure. The oil content and SDS addition had an effect over the microstructure and physical properties of HPMC-based emulsions which lead to different microstructures during film formation. The way that oil droplets were structured into the film had an enormous influence over the physical properties of HPMC films.
乳液的初始特性以及在成膜过程中油滴在薄膜基质中的重新排列，决定了其微观结构，对乳液基薄膜的物理性能起着重要作用。本工作的目的是研究 HPMC 水包油乳液的微观结构（两种油滴大小分布）和稳定性（有无表面活性剂）对 HPMC 乳液基可食用薄膜物理性能的影响。使用超声匀浆器，用 HPMC 制备葵花籽油的水包油乳液，油含量为 0.3%或 1.0%（w/w），有无 SDS 作为表面活性剂。测量乳液的微观结构、流变性能和稳定性（乳析）。此外，还评估了 HPMC 薄膜的微观结构、油滴聚结、表面自由能、光学和力学性能以及水蒸气传输性能。图像分析未显示出在不同油含量下制备的乳液的粒径分布有差异；然而，使用 SDS 可以将粒径分布转移到较低的值。无 SDS 时，含 0.3%和 1.0%油的乳液的体积平均直径分别为 3.79μm 和 3.77μm，含 SDS 时分别为 2.72μm 和 2.71μm。含 1.0%油的乳液稳定性更高，在无 SDS 和含 SDS 的乳液中分别储存 5 天和 3 天后，几乎没有变化。乳液基薄膜的内部和表面微观结构受油滴的聚结和乳析程度的影响。未发现微观结构对薄膜表面自由能的影响。油的加入由于光的散射而损害了薄膜的光学性质。添加油和 SDS 降低了乳液基薄膜的断裂应力。用油和 SDS 替代 HPMC 会导致薄膜中网络结构的“数量”减少，从而使薄膜结构变弱。油含量和 SDS 的添加对 HPMC 基乳液的微观结构和物理性能有影响，导致成膜过程中出现不同的微观结构。油滴在薄膜中的结构化方式对 HPMC 薄膜的物理性能有很大影响。
