红外烘烤对魔芋葡甘露聚糖表观黏度以及微观结构的影响

加热处理能降低魔芋葡甘露聚糖（konjac glucomannan，KGM）的黏度，并显著影响其理化性质。本实验以纯化魔芋微粉为原料，通过KGM水溶胶黏度、流变性质测定和KGM分子质量测定，KGM紫外吸收光谱、傅里叶变换红外光谱分析，以及KGM扫描电子显微镜观察，研究红外烘烤温度、时间对KGM表观黏度以及微观结构的影响。结果表明，随着烘烤温度升高和时间延长，KGM水溶胶的表观黏度均表现出典型的剪切稀化现象，储能模量（G’）和损耗模量（G”）明显下降；在剪切速率为10 s－1时，与未烘烤KGM水溶胶相比，150 ℃烘烤30 min的KGM水溶胶黏度下降了97.18%，180 ℃烘烤10 min的KGM水溶胶黏度下降了99.51%。扫描电子显微镜分析结果显示，烘烤热处理温度和时间均对KGM的微观结构造成了一定程度的破坏，但傅里叶变换红外光谱分析结果表明烘烤热处理对KGM分子重复单元结构与特征功能基团并未造成破坏，其特征基团结构得以保留，仅部分糖苷键及氢键断裂；分子质量测定结果表明，150 ℃烘烤30 min与180 ℃烘烤10 min均会明显降低KGM的分子质量。综上，红外烘烤热处理可作为热降解KGM的有效手段，其理化性质的改变可扩展其在食品、医药等领域的应用。

Effect of Infrared Baking on Apparent Viscosity and Microstructure of Konjac Glucomannan

Previous studies have confirmed that heat treatments can reduce the viscosity of konjac glucomannan (KGM), and significantly affect the physical and chemical properties. This study aimed to investigate the effect of infrared baking temperature and time on the viscosity and microstructure of KGM. The viscosity and rheological properties of KGM hydrosols and the molecular mass of KGM were measured and KGM was analyzed by ultraviolet spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The microstructure was observed by scanning electron microscopy (SEM). The results showed that the apparent viscosity of KGM hydrosols exhibited a typical shear-thinning behavior with the increase in baking temperature and time, and the elastic modulus (G’) and loss modulus (G”) increased markedly. The apparent viscosity at a shear rate of 10 s-1 decreased by 97.18% after 30 min of baking at 150 ℃, and by 99.51% after 10 min of baking at 180 ℃. Scanning electron microscopy (SEM) confirmed that the microstructure was disrupted by baking in a time-dependent and temperature-dependent manner. However, FTIR spectroscopy showed that baking treatment did not destroy the repeating unit structure or characteristic functional groups of KGM, retaining the basic structure in spite of some glycosidic and hydrogen bonds. Baking treatment at 150 ℃ for 30 min or 180 ℃ for 10 min greatly decreased the molecular mass of KGM. Therefore, infrared baking could be an effective way to decrease the viscosity of KGM, altering its physicochemical properties to extend its application in the food and medical fields.