Liposomes are commonly used delivery systems but exhibit limited applicability due to aggregation after storage. The stability of liposomes improves by modifying their surface properties by coating them with polyelectrolytes. Hence, this study investigated the applicability of complex coacervates containing 1% (w/w) citrus pectin and denaturated whey protein isolate (dWPI) formed at different pectin-protein mass ratios (r) at different pH to coat liposomes. Liposomes were prepared from egg lecithin (1% w/w) by fivefold membrane filtration (0.8 µm pore-diameter) and blended with pectin/dWPI-solutions using two approaches: (1) Coacervate formation at pH < isoelectric point (pI) of the protein (pH ~5.5) and subsequent coating of liposomes (pH 3.5), and (2) Mixing of biopolymers at pH > pI (at pH 5.5) of the protein, blending with liposomes (pH 5.5) followed by acidification to induce coacervate formation. Applicability was assessed by surface charge and particle diameter measurements. Approach 1 showed that the optimum conditions for coacervate formation and subsequent liposome coating were at r 1:1 - 1:7.5 and pH 3.9 and 5.1. At pH < 4.1, the liposomes coated with coacervates precipitated. In approach 2, the liposomes were prepared at a lower pH (3.5) than in approach 1 to induce electrostatic interactions between the liposomes and coacervates. The results showed that the optimum pH for forming complex coacervates and coating liposomes in situ was when pH was reduced to 4.6-3.5 and r set at 1:2.5 or 1:5 when using approach 2. After addition of maltodextrin (10%, w/w) and spray-drying, the liposomes coated with coacervates showed a powdery appearance and the re-suspended powder revealed similar particle diameters than prior spray-drying regardless of the approach. However, solutions prepared after approach 2 generally showed more precipitation, especially if biopolymer concentration was increased. Therefore, approach 1 can be considered as method of choice, as it requires one process step less, and leads to the formation of more physically stable particles.
Principal investigator: Prof. Jochen Weiss j.weiss@uni-hohenheim.de
