Abstract As a polyhydroxy carboxylic polymer, pectin is prone to physicochemical reactions under dehydration stress. This study investigated the molecular polymerization, structures and emulsifying properties of sugar beet pectin (SBP) after dry-heating at 45, 60, 75 and 110 °C for different lengths of time. When thermally treated, SBP molecules gradually cross-linked into insoluble and irregular-shaped flocs in a time- and temperature-dependent manner. The polymerized SBP was confirmed by high-performance size exclusion chromatography and dynamic light scattering techniques, and then morphologically characterized by a scanning electron microscope, which exposed a compact texture. Both soluble and insoluble SBP cross-linked polymers (named ISBP) were formed, depending on the dry-heating conditions. ISBP110 °C–2 h had a notably high protein content (16.2%), which evidenced the role of proteinaceous materials in constructing the cross-linked structures. Moreover, the FTIR and NMR spectroscopic bands relative to the amidation between amino and carboxyl groups suggested that SBP molecules might be covalently cross-linked with protein as the linker. The emulsifying properties of dry-heating treated SBP (75 °C for 12 h or 110 °C for 2 h) were significantly improved with the soluble cross-linked SBP with increased surface hydrophobicity. In that case, controlled dry-heating treatment could be employed as a simple method to improve the emulsifying activities of SBP. Altogether, this work demonstrates that the endogenous protein moiety plays an essential role in the polymerization of SBP under dry-heating, possibly via cross-linking SBP chains through the amidation with carboxyl groups of galacturonic acid residues.

中文翻译：

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控干加热法研究甜菜果胶的聚合及理化性质变化

摘要 作为一种多羟基羧酸类聚合物，果胶在脱水胁迫下容易发生物理化学反应。本研究研究了甜菜果胶 (SBP) 在 45、60、75 和 110 °C 干热不同时间后的分子聚合、结构和乳化性能。热处理后，SBP 分子逐渐交联成不溶性和形状不规则的絮凝物，并随时间和温度变化。通过高效尺寸排阻色谱和动态光散射技术确认聚合的 SBP，然后通过扫描电子显微镜对其进行形态表征，从而暴露出致密的纹理。根据干热条件，形成可溶性和不溶性 SBP 交联聚合物（称为 ISBP）。ISBP110 °C–2 h 具有显着高的蛋白质含量（16.2%），这证明了蛋白质材料在构建交联结构中的作用。此外，与氨基和羧基之间的酰胺化相关的 FTIR 和 NMR 光谱带表明 SBP 分子可能与作为接头的蛋白质共价交联。干加热处理的 SBP（75 °C 12 小时或 110 °C 2 小时）的乳化性能随着可溶性交联 SBP 的表面疏水性增加而显着改善。在这种情况下，可以采用控制干加热处理作为提高 SBP 乳化活性的简单方法。总之，这项工作表明内源性蛋白质部分在干热下 SBP 的聚合中起着至关重要的作用，