Effect of Confinement and Kinetics on the Morphology of Phase Separating Gelatin-Maltodextrin Droplets

Abstract

The effect of confinement on the structure evolution and final morphology during phase separation and gelation of gelatin and maltodextrin was investigated and compared to the structures seen in bulk phase. Emulsion droplets with diameters from 4 to 300 mum were analyzed using confocal laser scanning microscopy and image analysis. With the confocal laser scanning microscope it was possible to follow the entire phase separating process inside the droplets in real-time. The samples were either quenched directly from 70 degrees C down to 20 degrees C or exposed to holding times at 40 degrees C. Different cooling procedures were studied to examine the structure evolution both before and after gelation in the restricted geometries. The concentration of the biopolymer mixture was kept constant at 4 w/w% gelatin and 6 w/w% maltodextrin. The results revealed that the size of the confinement had a great effect on both the initiation of phase separation and the final morphology of the microstructure inside the emulsion droplets. The phase separation in small droplets was observed to occur at a temperature above the phase separating temperature for bulk. Small droplets had either a microstructure with a shell of maltodextrin and core of gelatin or a microstructure where the two biopolymers had formed two separate bicontinuous halves. The initiation of phase separation in large droplets was similar to what was seen in bulk. The microstructure in large droplets was discontinuous, resembling the morphology in bulk phase. The kinetics had an effect on the character of the maltodextrin inclusions, as the cooling procedure of a direct quench gave spherical inclusions with an even size distribution, while a holding time at 40 degrees C resulted in asymmetrical and elongated inclusions.

Confocal Raman microscopy for mapping phase segregation in individually dried particles composed of lactose and macromolecules

“…Furthermore, a large number of studies have been focused on phase separation in liquid mixed systems [20][21][22][23]. In a study by Fransson et al [24] the mixture of gelatin and maltodextrin was investigated. It was found, by recording in real time with the help of CLSM, that gelatin and maltodextrin started to phase separate after a short time (100 s) in droplets.…”

Aqueous Two-Phase Systems for Microencapsulation in Food Applications

“…A different approach to formation of coreÀshell microcapsules based on ATPS was taken by Wassén et al (Fransson et al, 2009;Wassen et al, 2012Wassen et al, , 2013. Their systems are based on a premixed polymer solution composed of two polymers in water and where the polymers will be phase separated.…”

“…Their systems are based on a premixed polymer solution composed of two polymers in water and where the polymers will be phase separated. The droplet size depended on the manufacturing technique, so that emulsification resulted in droplets in the range 4À300 μm (Fransson et al, 2009), while microfluidic manufacturing produced monodispersed droplets in the size range 115À160 μm (Wassén et al, 2012). Both gelatinÀmaltodextrin (temperature-induced gelation) and gellan gumÀwhey protein isolate (pH-induced gelation of preheated WPI) were used in the studies (Fransson et al, 2009;Wassén et al, 2013).…”

“…The holding time at a temperature above the gelation temperature strongly affected the internal structure in the droplets, so that immediate cooling to 20 C did not allow for as extensive a phase separation as a longer holding time (5À20 minutes) before cooling to 20 C (Fransson et al, 2009). The holding time at a temperature above the gelation temperature strongly affected the internal structure in the droplets, so that immediate cooling to 20 C did not allow for as extensive a phase separation as a longer holding time (5À20 minutes) before cooling to 20 C (Fransson et al, 2009).…”

Coupling process of phase separation and gelation in konjac glucomannan and gelatin system

“…The microstructures are trapped at the early stages of phase separation and then coarsening changes are blocked by gelation. But it did not prevent drop coalescence of microstructure even gelation hindered the phase separation (Fransson, Lor en, Altsk€ ar, & Hermansson, 2009). …”