Abstract: The thermal stability characteristics of konjac glucomannan oligosaccharides and fructooligosaccharides was tested with a thermogravimetric analyzer under different heating rates. The activation energy (E), pre-exponential factors (ln A), thermodynamic parameters and mechanism functions of the two oligosaccharides were calculated by Kissinger method, Kissinger-Akahira-Sunose (KAS) method and Flynn-Wall-Ozawa (FWO) method and the mechanism equations were determined. The results showed that the pyrolysis process of both oligosaccharides was divided into 3 stages, and the peak temperature of decomposition was 220–300 ℃ under the non-isothermal heating rate. The first stage is the process of oligosaccharides drying and dehydration. At the second stage, the E and ln A of fructooligosaccharides were greater than those of glucomannan oligosaccharides, showing that the former was depolymerized by heat to produce fructodisaccharide and fructotrisaccharide, which can rapidly crystallize leading to a high E. The mechanism function of glucomannan oligosaccharides followed the three-dimensional spherically symmetric diffusion Jander equation. At the third stage, the E and ln A of glucomannan oligosaccharides were higher, showing that the thermal stability was higher than that of fructooligosaccharides. The mechanism functions of both oligosaccharides followed the random nucleation and subsequent growth of Avrami-Erofeev equation. Finally, the thermodynamic parameters of the oligosaccharide pyrolysis process, namely ΔG, ΔH and ΔS, were determined. The obtained thermal stability of glucomannan oligosaccharides and fructooligosaccharides provides a basis for the design of processing technology for foods and medicine.

Key words: glucomannan oligosaccharides; fructooligosaccharides; oligosaccharides; prebiotics; thermomechanical analysis