Measurement of dynamic rheology during ageing of gelatine-sugar composites

The effect of sugars (sucrose, glucose and xylose) at different concentrations (0, 10, 20, 30, 40 and 50%) on the dynamic rheological properties of gelatine (2% w/w) was investigated during ageing. Storage moduli (G'), when measured at 5 degreesC, decreased with increasing concentration of added sugar. Xylose was found to induce the greatest reduction in the values of G'. G' values, measured as a function of ageing time (10 h) at 5 degreesC, increased rapidly at the initial stage and then reached a pseudoplateau region after long ageing times. Increasing the sugar concentration resulted in a decrease in the pseudoplateau values. The rate constant (K) for structure development of gelatine during ageing was described by apparent first-order kinetics. G' and K values in gelatine-sugar composites increased in the following order: xylose < glucose < sucrose. The magnitudes of G' at the end of ageing were much greater than those of G'', showing a small dependence (slope = 0.005-0.088) on frequency (omega).