Optimization of Microwave-assisted Semidry Degradation of Konjac Glucomannan with Hydrogen Peroxide and Its Characteristics

The processing efficiency and application range of konjac glucomannan (KGM) are limited because of its high relative molecular mass and the high viscosity of its aqueous solution. In this study, konjac flour from Amorphophallus bulbifer was used as raw material to develop an efficient approach to reducing the viscosity of KGM and broadening its application market. Based on a single-factor test and an orthogonal experimental design for optimization, low-viscosity konjac flour was prepared by microwave-assisted hydrogen peroxide oxidation (a semidry process), and the changes in physicochemical, structural, and physiological characteristics of KGM were characterized before and after the treatment. The results showed that the viscosity of konjac flour decreased from 6341.67±52.04 to 53.33±5.77 mPa·s, and the weight-average molecular weight of KGM decreased from 347.31 to 158.26 kDa when the uniformly mixed reactants were heated and reacted within 3 min at a microwave power of 700 W. The concentration of the hydrogen peroxide was 3%, and the liquid-material ratio was 0.75:1 mL/g. Compared to the untreated raw material, it decreased by 99.16% and 54.43%, respectively. Based on X-ray diffractometry, ultraviolet-visible spectrometry, infrared spectrometry, and scanning electron microscopy analyses of the KGM structure before and after oxidation, the oxidation of the KGM degraded the KGM molecular chain, decreased the crystallinity, and damaged the microscopic lamellar structure while retaining the characteristic groups. Moreover, the effect of the microwave-assisted hydrogen peroxide in decreasing the viscosity of the KGM was superior to that of the KGM treatment with the microwave or hydrogen peroxide only. The degradation products exhibited better fat-binding capacity and bile-acid-binding capacity. Therefore, KGM can be produced in a highly efficient, green, and ecofriendly manner, providing a rationale for the development and utilization of low-viscosity KGM.