Analysis of the hydrolysis of inulin using real time 1H NMR spectroscopy

The hydrolysis of various carbohydrates was investigated under acidic conditions in real time by ¹H NMR spectroscopy, with a focus on the polysaccharide inulin. Sucrose was used as a model compound to illustrate the applicability of this technique. The hydrolysis of sucrose was shown to follow pseudo first order kinetics and have an activation energy of 107.0 kJ mol ^-1 (SD 1.7 kJ mol^-1). Inulin, pullulan and glycogen also all followed pseudo first order kinetics, but had an initiation phase at least partially generated by the protonation of the glycosidic bonds. It was also demonstrated that polysaccharide chain length has an effect on the hydrolysis of inulin. For short chain inulin (DPn 18, SD 0.70) the activation energy calculated for the hydrolytic cleavage of glucose was similar to sucrose at 108.5 kJ mol^-1 (SD 0.60). For long chain inulin (DPn 30, SD 1.3) the activation energy for the hydrolytic cleavage of glucose was reduced to 80.5 kJ mol^-1 (SD 2.3 kJ mol^-1). This anomaly has been attributed to varied conformations for the two different lengths of inulin chain in solution.