Abstract Pectin powder is degraded during storage and transport by demethoxylation and depolymerisation. The degradation mechanisms and especially the influence of pre-treatments on the degradation reactions are not completely understood. In this study, commercial citrus pectin was modified by either acidic or alkaline demethoxylation. The modified pectins, as well as the commercial pectin, were thermally degraded during four weeks of storage at 60 °C and 80% relative humidity. Demethoxylation and depolymerisation as well as colour alterations were examined during degradation, and the course of the reactions was monitored. It was found that the type of pre-treatment during modification determined the material properties and, thus, the water uptake of the modified pectin powders. The resulting water availability in the samples was crucial to the extent of demethoxylation and to the type and intensity of depolymerisation since some of these reactions competed for the water in the climate chamber. The pre-treatment also determined the content of neutral sugars and sodium ions of the modified pectins. High contents of these components limited the extent of degradation in different ways. A previously assumed third depolymerisation mechanism of pectins, beside backbone hydrolysis and β-elimination, was confirmed.

中文翻译：

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柑橘果胶粉的热降解-酸性和碱性预处理的影响

摘要 果胶粉在储存和运输过程中通过脱甲氧基和解聚作用降解。降解机制，尤其是预处理对降解反应的影响尚不完全清楚。在这项研究中，商业柑橘果胶通过酸性或碱性脱甲氧基化进行了修饰。在 60 °C 和 80% 相对湿度下储存 4 周后，改性果胶以及商业果胶都发生了热降解。在降解过程中检查脱甲氧基和解聚以及颜色变化，并监测反应过程。发现改性过程中的预处理类型决定了材料特性，从而决定了改性果胶粉末的吸水率。样品中由此产生的水可用性对于脱甲氧基化的程度以及解聚的类型和强度至关重要，因为这些反应中的一些与气候室中的水竞争。预处理还测定了改性果胶的中性糖和钠离子的含量。这些成分的高含量以不同的方式限制了降解的程度。除了骨架水解和β-消除之外，先前假设的果胶的第三种解聚机制得到证实。这些成分的高含量以不同的方式限制了降解的程度。除了骨架水解和β-消除之外，先前假设的果胶的第三种解聚机制得到证实。这些成分的高含量以不同的方式限制了降解的程度。除了骨架水解和β-消除之外，先前假设的果胶的第三种解聚机制得到证实。