Although the glass transition properties and encapsulation efficiency of various biopolymers have been documented, no attempts have been made to relate the alpha-relaxation behavior, molecular structure and stability of an encapsulation system above the glass transition. In this work, the efficiency of whey protein (W), maltodextrin (M) and their combination (MW) to encapsulate alpha-mangostin was assessed through the monitoring of the changes in the mechanical property and molecular structure around the glass transition using dynamic-mechanical analysis and Fourier transform infrared spectroscopy, respectively. A dramatic decrease in the storage modulus was observed in the non-encapsulation system (NE). Addition of W and M increased the temperature difference (T-storage - T-alpha), resulting in a decrease in the alpha-mangostin degradation rate during storage. Carbonyl group (C - H) vibration of reducing sugars became smaller when W was added, while the spectra of the M and MW systems exhibited sharp peaks. This confirmed better encapsulation with W than with M. (C) 2015 Elsevier Ltd. All rights reserved.