Structure-related degradation of pectins and their impact on non-enzymatic browning and technological functionality

食品的加工和储存导致生物聚合物成分的化学和生物化学变化。因此，它们的功能特性通过非酶布朗宁反应和氧化过程而改变。与还原糖相比，糖醛酸作为Maillard反应的前体很少被研究。因此，应研究果胶降解的反应过程、中间产物和反应产物及其在非酶布朗宁反应中的作用。在模型系统中，第一个结果表明，与还原糖相比，糖醛酸的显色速度更快。然而，水解和β-消除裂解不能提供充分的解释。此外，果胶的热诱导降解的中间体，如饱和和4，5-不饱和寡聚半乳糖醛酸没有系统地表征。关于改性果胶的功能特性，应该有进一步的研究兴趣。本课题的目的是研究和阐明果胶热降解的反应机理。更确切地说，应阐明起始材料的结构和所用条件对形成的中间体的影响及其在非酶促布朗宁（美拉德反应）颜色形成中的作用。出于这个原因，将分别使用半乳糖醛酸及其甲酯的不同模型系统。纯化的部分甲基酯化的饱和和不饱和寡聚半乳糖醛酸应分别用于进一步的模型。此外，该结果应提供一个洞察果胶降解的机制和由此产生的影响，降解产物的物理化学特性。先前执行的差示扫描量热法显示异常，并假设降解机制。作为该项目的一部分，化学调查和结构分析表征的比较可以证实我们假设的降解机制。最后，应检查降解对果胶功能特性的影响。因此，应将NMR光谱法鉴定的结构与物理化学性质研究期间获得的结果进行比较。

Processing and storage of food lead to chemical and biochemical changes in the biopolymeric constituents. Consequently, their functional properties modified by non-enzymatic browning reactions and oxidative processes. In contrast to reducing sugars, uronic acids as precursors in the Maillardreaction have rarely been studied. Hence, reaction processes, intermediates and reaction products of pectin degradation and their role in non-enzymatic browning reactions should be investigated. In model systems first results show a faster color development of uronic acids in comparison with reducing sugars. However, the hydrolytic and beta-eliminative cleavage does not provide a sufficient explanation. Additionally, the intermediates of the thermal induced degradation of pectins like saturated and 4,5-unsaturated oligogalacturonic acids are not systematically characterized. Regarding to the functional properties of modified pectins, further studies should be of interest. Objective of the project is to investigate and clarify the reaction mechanism of the thermally induced degradation of pectin. More precisely, the influence of the structure of starting materials and conditions used on intermediates formed and their role in color formation by the non-enzymatic browning (Maillard-reaction) should be elucidated. For this reason, different model systems will be used with galacturonic acid and its methyl ester, respectively. The purified partially methyl esterified saturated and unsaturated oligogalacturonic acids should be used separately in further models. Furthermore, the results should provide an insight into the mechanism of pectin degradation and the resultant effect to the physico-chemical characteristics of degradation products. The previously executed differential scanning calorimetry shows anomalies and a mechanism of degradation is postulated. The comparison of chemical investigations and structure-analytical characterizations as a part of the project could confirm our postulated degradation mechanism. Finally, the influence of degradation on functional properties of pectin should be examined. For this reason structures identified by NMR spectroscopy should be compared with results obtained during investigation of physico-chemical properties.