Preparation of alginate microgels in a simple one step process via the Leeds Jet Homogenizer

Fine calcium alginate microgel particles, down to particle sizes lower than 100 nm, were produced using a Jet Homogenizer previously developed in the School of Food Science and Nutrition (University of Leeds, Leeds, UK) consisting of highly turbulent mixing of two liquid streams of sodium alginate and calcium chloride solution. The final mean particle size, d, depended on the alginate to calcium ratio. From 0.5 to 2 wt.% alginate in the presence of 1-10 and 20 mM Ca2+, d was lower than 5 μm and higher than 20 μm, respectively. However, d was not so significantly affected by the homogenization pressure above 150 bar at room temperature (20 ± 3 °C) or the volume ratio of the sodium alginate to calcium chloride solutions, within the limits 1:9 or 9:1. The particles initially exiting the homogenizer appeared to be slightly aggregated since sonication produced a further decrease in size. The particles were negatively charged (-31.7 mV ± 3.1 mV at pH 8) and inclusion of a suitable globular protein (lactoferrin but not lysozyme) of opposite charge led to a further reduction particle size and a slight decrease in particle ζ-potential. It is suggested that some degree of protein adsorption to the particle surface occurred, akin to a surfactant, which helped to control the particle size. In addition, some lactoferrin may also be incorporated inside the microgel particles during their formation, highlighting the potential of this technique to encapsulate various materials within microgel particles formed from Ca2+ cross-linked biopolymers