Abstract: 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.

Key words: konjac glucomannan; infrared baking; apparent viscosity; microstructure; molecular mass