Abstract Aim of the present study was to investigate the impact of different demethoxylation methods and the co-occuring side effects on the molecular properties and structure formation in pectin gels. A high-methoxylated citrus pectin (HMP) was demethoxylated using either hydrochloric acid or pectin methylesterases of plant (pPME) or fungal (fPME) origin. pPME treatment causes a more block-wise distribution of free carboxyl groups, fPME or acidic treatment a random distribution. Twelve pectin samples with four different degrees of methoxylation (DM) between 62% and 41% were prepared. The gelation process was studied by oscillatory measurements. In pectin samples from pPME treatment structure formation started at higher temperature and the final gels were more elastic in comparison to pectin from the two other modifications. The impact of the block-wise distribution of the free carboxyl groups became more evident with decreasing DM. The gelling process of pectin samples with random distribution was similar independent of DM.Side effects of all demethoxylation reactions were an altered sodium ion content (high in enzymatically treated pectin, close to zero in acidic treated) and a decrease of the molecular weight with increasing degree of demethoxylation. These side effects additionally altered the gelation process and the final gel properties in different ways.

中文翻译：

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酶促和酸性脱甲氧基化对含糖柑橘果胶凝胶结构形成的影响

摘要 本研究的目的是研究不同脱甲氧基化方法的影响以及同时发生的副作用对果胶凝胶分子性质和结构形成的影响。使用盐酸或植物 (pPME) 或真菌 (fPME) 来源的果胶甲酯酶使高甲氧基化柑橘果胶 (HMP) 脱甲氧基。pPME 处理导致游离羧基更呈块状分布，fPME 或酸性处理导致随机分布。制备了 12 个具有 62% 至 41% 之间四种不同甲氧基化度 (DM) 的果胶样品。通过振荡测量研究凝胶化过程。在来自 pPME 处理结构的果胶样品中，在较高温度下开始形成，与来自其他两种修饰的果胶相比，最终凝胶更具弹性。随着 DM 的减少，游离羧基的嵌段分布的影响变得更加明显。随机分布的果胶样品的胶凝过程与 DM 无关。所有脱甲氧基反应的副作用是钠离子含量改变（酶处理的果胶高，酸处理的果胶接近零）和分子量随着脱甲氧基的程度。这些副作用还以不同的方式改变了凝胶化过程和最终的凝胶特性。在酸性处理中接近于零）并且分子量随着去甲氧基化程度的增加而降低。这些副作用还以不同的方式改变了凝胶化过程和最终的凝胶特性。在酸性处理中接近于零）并且分子量随着去甲氧基化程度的增加而降低。这些副作用还以不同的方式改变了凝胶化过程和最终的凝胶特性。