61A-17

We are using luminescence spectroscopy to study the dynamics of amorphous sucrose in an effort to develop additional methods to directly monitor molecular mobility in amorphous solid foods.  Erythrosin B (FD&C red#3) was doped into sucrose glasses to investigate its utility as a probe of matrix molecular mobility.  The phosphorescence lifetimes (t) of Erythrosin B were determined as a function of temperature (T) from 3-77^oC in the absence of O₂.  Lifetimes decreased monotonically from 750-500ms with increasing T and the system exhibited hysteresis from 15-77°C, with lifetimes on cooling ~10% higher than those determined during the heating cycle.  An Arrhenius plot of the log of the phosphorescence decay rate (1/t) versus 1/T showed two different slopes with a break at ~60^oC, near the Tg of dry sucrose, indicating that both the rate and the activation energy for collisional quenching due to matrix molecular mobility increased at T>Tg.  Delayed fluorescence (DF) and phosphorescence (P) emission spectra were obtained from 4-85^oC. The emission of DF and P were both red-shifted (lower energy); DF intensity is increased while P intensity is decreased with increasing T. A plot of the log of the ratio of peak intensities (log{I_DF/I_P}) versus 1/T was linear, signifying Erythrosin B as molecular temperature sensor.  The phosphorescence emission was lower energy (longer wavelength) when excited at 560 nm than at 530 nm, the energy difference decreased at higher T indicating greater matrix dipolar relaxation due to mobility at higher T; excitation energy had no influence on the emission in mobile aqueous sucrose.  An Arrhenius-type plot of the log of inverse energy difference upon excitation at 530nm and 560nm versus 1/T had a sharp break at T~60^oC, suggesting a novel relaxation process was introduced at T>60^oC.  These results demonstrated the validity of luminescence to study molecular mobility in amorphous sugar glasses.