The role of suspension rheology on the size and morphology of complex coacervated microcapsules

The rheological behavior of the suspensions forming the microcapsules by complex coacervation is a determining factor in defining the final size and shape of the microcapsules. In this study, two suspensions were used to produce microcapsules by complex coacervation, one suspension formed by gelatine/gum Arabic and the other by gelatine/sodium alginate, to observe the influence of suspensions on the formation of microcapsules. The microcapsules produced were evaluated through optical microscopy, particle size analysis, encapsulation efficiency, color measurements, and Fourier-transform infrared spectroscopy (FTIR). Gelatin/gum Arabic and gelatin/sodium alginate suspensions resulted in different rheological behaviors: shear-thickening and shear-thinning, respectively. Both biopolymer combinations proved to be efficient for complex coacervation, resulting in microcapsules with size values ranging from 37µm to 112µm in the case of gelatin/gum Arabic, and 29µm to 55µm for gelatin/sodium alginate. However, the production and the size of the microcapsules were influenced by the processing conditions: the shear-thickening suspension led to better results at low stirring speeds, whereas the shear-thinning suspension showed better results at high stirring speeds.