Crystallization and strength analysis of amorphous maltose and maltose/whey protein isolate mixtures

Maltose is an essential derivative of starch. To understand the processability and stability of maltose-containing foods, material characterization of the phase and state transition from its amorphous state is required. Although the crystallization of amorphous maltose is well understood, few studies have reported the relationship between the crystallization and the glass transition temperature (T_g )-related molecular mobility. In this study, water sorption, crystallization, T_g -related α-relaxation, and the corresponding time factor for amorphous maltose and maltose / whey protein isolate (WPI) mixtures are measured at various water activity (a_w ) levels and 25 °C.

The water-additive principle for maltose / WPI mixtures was observed at a_w  ≤ 0.440 at the molecular level, whereas the crystallization of amorphous maltose occurred at high a_w values (≥0.534). The crystal formation and crystallization kinetics of amorphous maltose were affected by water and WPI at a_w  ≥ 0.534 and 25 °C, as determined by X-ray diffraction. The relationship between T_g and the water content was fitted by the Gordon-Taylor model, and its constant showed a compositional dependence for the maltose / WPI mixtures. The α-relaxation temperature of the amorphous samples decreased due to water plasticization, but increased with an increase in the WPI quantity. The Strength (S) value for amorphous maltose, which was a quantitative estimate of the compositional effects on molecular mobility, was based on the William-Landel-Ferry (WLF) equation.

The S concept exhibits considerable potential for application in controlling the crystallization of amorphous maltose and improving the processability and stability of maltose-containing foods. © 2020 Society of Chemical Industry.