An efficient and simple approach for the controlled preparation of partially degraded konjac glucomannan

The degraded konjac glucomannan (KGM) has been reported to have health benefits and changes in rheological properties. In this study, partially degraded konjac glucomannan (PDKGM) with the weight-average molecular weight (Mw) in a range of 8 kDa–420 kDa was prepared by an efficient method named heterogeneous hygrothermal degradation. That is, solid state KGM powder containing a certain moisture content was placed in an autoclave and hygrothermal treated at 121 °C for a period of time; after removing from the autoclave and drying, dried PDKGM powder can be obtained. This method avoids hydrating KGM into sol for hydrolysis and then removing a large amount of water to obtain dried degraded KGM. The structure and properties of the PDKGM were characterized by SEC-MALLS, FT-IR, DSC, XRD, AFM and rheological test. The kinetic model of heterogeneous hygrothermal degradation was established to forecast the relationship between degradation conditions and Mw of KGM. Results indicated that this approach can obtain PDKGM with specified molecular weight and narrow molecular weight distribution through the control of processing time and initial moisture content of KGM powder. Meanwhile, it was also a facile method that can steeply reduce the apparent viscosity of KGM. Since no special equipment or complicated processes are required, we believe this is a realistic KGM degradation strategy with potential for use in industry.