Preparation, characterization and physicochemical properties of Konjac glucomannan depolymerized by ozone assisted with microwave treatment

The degradation and modification can greatly improve solubility properties of Konjac glucomannan (KGM) and enhance its capacity to interact with other polymers. Hereby, low-viscosity oxidized KGM (OKGM) was prepared by a combined method of ozone assisted with microwave. In this study, we mainly discussed the effect of ozonemicrowave treatment on the structure and properties of KGM. The experimental results indicated that ozonemicrowave treatment caused a time-dependent (30, 60, 80, 100, 120 min) degradation of KGM, and longer treatment time led to lower molecular weight (Mw) and apparent viscosity of KGM. The OKGM depolymerized by 120 min ozone-microwave showed a good water solubility index (85.08%) and low swelling power (4.29 g/g). Besides, determination of carbonyl contents showed that ozone-microwave introduced more carbonyl contents into KGM than ozonation alone. Moreover, FT-IR and XRD spectra suggested that the chemical structure and crystallized region of native KGM was altered after ozone-microwave treatments. Compared to native KGM, the thermal stability of OKGM decreased while its whiteness was enhanced. In addition, the rheological properties of OKGM differed markedly from native KGM due to the changes in Mw and molecular structure. This study provides a new pathway for efficiently producing depolymerized KGM to meet some practical production needs, and may be useful for future research and development of OKGM.