Bacterial Exopolysaccharides - Relationship between chemical structure, intrinsic viscosity and technofunctionality

亲水胶体通常用于各种食品中，以改善质地和稳定性。乳酸菌的使用能够在发酵过程中产生胞外多糖(EPS)，这可能大大有助于开发具有尽可能少添加剂的清洁标签产品。乳酸菌合成的均多糖和杂多糖具有高度的结构异质性，这导致它们的大分子特性以及特性粘度和技术功能性质有很大的差异。在我们的上述项目中，我们获得了以下知识：从不同的嗜热链球菌菌株中重复合成足够量的EPS，在不改变结构的情况下进行温和的分离程序，以及EPS的大分子和技术功能特性。此外，与Wefers基团合作对选定的EPS的分子结构进行了评估。然而，由于乳酸菌EPS的高度结构异质性和多种影响因素，关于分子结构对EPS技术官能化的影响知之甚少。本项目的目的是在单一结构属性(支化度、糖苷键、分子质量)与所选EPS的特性粘度以及技术官能度之间建立明确的关联。为此，选择的α在生物反应器中原位合成，并使用重组酶非原位合成HEPs-葡聚糖。合成条件的变化以及随后的机械和酶修饰产生EPS样品，它们只在一个结构属性(例如支化度)上不同，而不是它们的分子质量。为了更详细地分析EPS的结构特性，将使用现有的现代分析方法以及新开发的指纹方法。后者是基于对低聚糖的层析分析，这些低聚糖是通过部分酸解或如果可能的话，通过特定的酶释放出来的。我们希望对EPS的分子结构与大分子和技术功能特性之间的关系有良好的了解，这些知识可以转移到进一步的EPS中。

Hydrocolloids are commonly used in various foods to improve texture and stability. The use of lactic acid bacteria, which are able to produce exopolysaccharides (EPS) during fermentation, may significantly contribute to the development of clean-label products with as few additives as possible. The homo- and heteropolysaccharides synthesized by lactic acid bacteria show a high structural heterogeneity, which results in large differences in their macromolecular characteristics and hence, in their intrinsic viscosity and technofunctional properties. In our foregoing projects, we gained knowledge on the reproducible synthesis of sufficient amounts of EPS from different Streptococcus thermophiles strains, on gentle isolation procedures without structural changes, and on the macromolecular and technofunctional properties of the EPS. In addition, the molecular structure of selected EPS was evaluated in cooperation with the Wefers group.However, because of the high structural heterogeneity of EPS from lactic acid bacteria and the multiple factors of influence, less is known about the effects of the molecular structure on the EPS technofunctionality.The aim of this project is to establish unambiguous correlations between single structural attributes (degree of branching, glycosidic linkages, molecular mass) and the intrinsic viscosity as well as the technofunctionality of selected EPS. For this purpose, selected HePS are synthesized in situ in a bioreactor and selected α-glucans are synthesized ex situ by using recombinant enzymes. Variation of synthesis conditions as well as subsequent mechanical and enzymatic modifications yield EPS samples, which differ only in one structural attribute (for example the degree of branching), but not their molecular mass. For a more detailed analysis of the structural properties of the EPS, established modern analytical approaches as well as newly developed fingerprinting methods will be used. The latter are based on the chromatographic analysis of oligosaccharides which are liberated by partial acid hydrolysis or, if possible, by specific enzymes. We expect sound knowledge on the relationship between the molecular structure and the macromolecular and technofunctional properties of EPS, which can be transfered to further EPS.