Effects of Bloom number on phase transition of gelatin determined by means of rheological characterization

Abstract

This study shows the impact of the Bloom number on the melting and gelation behavior of porcine gelatin. Different batches of gelatin were prepared in concentrations of 2, 3, and 5 wt% having Bloom numbers of 100, 180, 240, and 260. Using asymmetrical flow field-flow-fractionation, the molecular weight of gelatin was determined. It was observed that higher Bloom numbers correspond to higher molecular weights. Systematic strain and temperature sweep tests were conducted to determine the yielding point and the phase transition temperatures. The latter was established by the crossover point method and the Winter-Chambon criterion, and small differences between these two methods were recorded. By increasing the Bloom number, the dynamic moduli were increased, as well as the gelation and melting temperatures. The same trend is valid for the gelatin concentration. On the other hand, the Bloom number does not considerably affect the yielding phenomenon under large amplitude oscillatory shear deformations. In conclusion, the Bloom number has a similar rheological effect on gelatin as the molecular weight, and considerable alterations of the viscoelastic gel properties can be expected at significantly different Bloom numbers.