Technische Universität Berlin, Institute for Food Technology and Food Chemistry, Department of Food Technology and Food Material Science, Königin-Luise-Str.22, 14195 Berlin, Germany.
Adv Colloid Interface Sci. 2017 May;243:105-113. doi: 10.1016/j.cis.2017.02.008. Epub 2017 Mar 1.
Saponins are interfacially active ingredients in plants consisting of a hydrophobic aglycone structure with hydrophilic sugar residues. Variations in aglycone structure as well as type and amount of sugar residues occur depending on the botanical origin. Saponins are a heterogeneous and broad class of natural substances and therefore the relationship between molecular structure and interfacial properties is complex and, yet, not completely understood. A wide range of research focused either on structural elucidation of saponins or interfacial properties. This review combines recent knowledge on structural features with interfacial properties and draws conclusions on how saponin structure affects interfacial properties. Fundamental understanding on interfacial configuration of individual saponin molecules at the interface distinctly increased. It was shown that interfacial configuration may differ depending on botanical origin and thus structure of the saponins. The formation of strong viscoelastic interfacial films by some saponins was attributed to hydrogen bonds between neighboring sugar residues. Few studies analyzed the relationship between botanical origin and interfacial rheology and derived main conclusions on important structural features. Saponins with a triterpenoid structure are most likely to form viscoelastic films, which result in stable foams and emulsions. The aglycone subtype may also affect interfacial properties as triterpenoid saponins of oleanane type formed most stable interfacial networks. But for more reliable conclusions more saponins from other aglycone subtypes (dammarane, ursolic) have to be analyzed. To-date only extracts from Quillaja saponaria Molina are approved for food products and many studies focused on these extracts. From experiments on interfacial rheology a reasonable model for supramolecular structure of Quillaja saponins was developed. It was further shown that Quillaja saponins may form micelles loaded with hydrophobic substances, nano-emulsions and stable foams. In combination proteins an increase in interfacial film stability may be observed but also negative phenomena like aggregation of oil droplets in emulsions may occur.
皂苷是植物中具有界面活性的成分，由疏水糖苷结构和亲水糖残基组成。糖苷结构的变化以及糖残基的类型和数量取决于植物的来源。皂苷是一类异质的、广泛的天然物质，因此分子结构与界面性质之间的关系是复杂的，而且尚未完全理解。大量的研究集中在皂苷的结构阐明或界面性质上。本综述将最近关于结构特征与界面性质的知识结合起来，并得出关于皂苷结构如何影响界面性质的结论。对单个皂苷分子在界面上的界面构型的基本理解明显增加。结果表明，界面构型可能因植物来源的不同而有所不同，因此皂苷的结构也不同。一些皂苷通过氢键在相邻糖残基之间形成强的粘弹界面膜。少数研究分析了植物来源与界面流变学之间的关系，并得出了关于重要结构特征的主要结论。具有三萜结构的皂苷最有可能形成粘弹界面膜，从而形成稳定的泡沫和乳液。糖苷元类型也可能影响界面性质，因为齐墩果烷型三萜皂苷形成了最稳定的界面网络。但是，为了得出更可靠的结论，还需要分析其他糖苷元类型（达玛烷、熊果酸）的更多皂苷。迄今为止，只有 Quillaja saponaria Molina 的提取物被批准用于食品，并且许多研究都集中在这些提取物上。通过界面流变学实验，开发了一种合理的 Quillaja 皂苷超分子结构模型。进一步表明，Quillaja 皂苷可能形成负载疏水物质的胶束、纳米乳液和稳定的泡沫。与蛋白质结合时，可能会观察到界面膜稳定性的增加，但也可能会出现负面现象，如乳液中油滴的聚集。
