脱乙酰魔芋葡甘聚糖独特低温加工特性及机制研究

In view of the distinctive processing characteristics of deacetylated konjac glucomannan-water system (Da-KGM) under low temperature, it was found by this research group that the low temperature above the freezing point obviously promoted the gel strength and lead to fibration when the system went through dissolution, freeze and freeze thawing. The functional mechanisms and the transformation regulations have not been reported yet. The reveal of the mechanism and regulation, however, is expected to provide a new perspective for konjac in the application research of food manufacturing. Therefore, in this research, Da-KGM of different deacetylation degree was employed as material. To clarify the mechanism of the promotion effect of low temperature on dissolution and gel strength from the point of view of secondary interaction, several methods have been taken, including CP/MAS, liquid-state 13C NMR, FT-IR, DSC, super resolution TEM and WAXD, to systematacially study the structure feature of solvent, solute and solution under various low temperatures in Da-KGM-water system. Further, to study the transformation regulation of rheological properties, texture properties, water migration and micorstructure, several approaches have been employed, such as dynamic rheology, TPA, Low Field Nuclear Magnetic Resonance and SEM. The research results have great significance to enrich the still weak polysaccharide low temperature processing theory, to provide references to the extraction and application of insoluble polysaccharides environmentally-friendly, and to offer theoretical and statistic support propelling Da-KGM to become a food ingredient with novel characteristics.

脱乙酰魔芋葡甘聚糖（Da-KGM）/水体系在低温区域存在一系列独特的加工特性，本课题组前期发现溶剂冰点以上的低温下明显促其溶解、冷冻及冻融中凝胶强度剧增或纤维化等现象，但其发生机制及藉此产生的性能变化规律均未见报道。而这些机制和规律的揭示，可望为魔芋在食品制造中的研究和应用提供一个新视角。因此,本课题拟以不同脱乙酰度的Da-KGM为材料，采用CP/MAS及液态 13C NMR、变温FT-IR、DSC、超分辨TEM、WAXD等手段，系统研究Da-KGM/水体系中，在不同低温处理条件下溶剂、溶质及溶液的相关结构特征，试图从次级相互作用角度阐明低温促溶及冻融凝胶增强的相关机制；采用动态流变、TPA、低场核磁、SEM等手段研究低温加工中流变性、质构、水分迁移及微观结构等变化规律。研究可丰富目前尚显薄弱的多糖低温加工理论，也为发展Da-KGM为一类具有新颖特性的食品配料提供直接的理论和数据支持。

本项目确证了不同脱乙酰度魔芋葡甘聚糖（KGM）的低温溶解影响因素，研究了低温溶解的Da-KGM溶液流变行为和凝胶特性，探索了低温促进脱乙酰魔芋葡甘聚糖（Da-KGM）溶解的机制，研究了冷冻致Da-KGM凝胶增强行为及机制。.溶解度实验结果表明Da-KGM最佳溶解温度为-4℃，在-4-10℃间的溶解度曲线遵循阿伦尼乌斯方程。最佳溶剂为9wt% KSCN。分析了Da-KGM在溶剂中的分子结构。Da-KGM/10wt%尿素水溶液和Da-KGM/9wt% KSCN水溶液体系中脱乙酰KGM分子发生自卷形成类螺旋结构，其结构变得有序，两种溶剂均加强了分子内的作用力。探讨了Da-KGM溶液的流变性质。脱乙酰度越高，脱乙酰KGM的零切粘度越低，低频区产生的平台区越平缓。脱乙酰KGM溶液在剪切作用下凝胶化时间随脱乙酰KGM溶液浓度升高、脱乙酰度降低、温度降低而减少。温度扫描结果表明脱乙酰KGM溶胶显示典型的热致凝胶行为。.探讨了脱乙酰KGM低温促溶机制。DSC、变温FT-IR、粘度测试表明KSCN水溶液中存在KSCN水合物，低温下，KSCN水合物与自由水间通过氢键网络形成较大尺寸的复合物结构，且低温促使脱乙酰KGM与KSCN水合物结合，阻止其分子间自聚，从而达到溶解效果。CP/MAS 13C NMR结果表明脱乙酰KGM溶解后分子链结构变得更有序，并且没有形成新的衍生物，表明9wt% KSCN是脱乙酰KGM的非衍生化的溶剂。.不同浓度的Da-KGM凝胶在冷冻后全质构指标均发生了变化，样品浓度越高，冷冻后硬度增幅越大。当KGM初始浓度为5 wt%时，冷冻后硬度增幅达到2950%。在实验设定的温度范围内，于-30℃冷冻的凝胶硬度最大。凝胶样品的硬度在冻融1次后达到最大值，此后随着冻融次数的增多而降低。上述结果表明恰当的冷冻工艺是调控凝胶质构的有效手段。通过在凝胶制备中加入尿素、SDS、NaCl等对可能影响多糖分子间作用力的物质并结合解胶实验，提示维系冷冻Da-KGM凝胶的作用力不仅有氢键作用力，可能还有疏水相互作用。