Microencapsulation of bioactives by in situ complex coacervation during spray drying

Complex coacervation is a phase separation of a mixture into two immiscible liquid phases mainly due to electrostatic interactions between two oppositely charged polymers. Microencapsulation by complex coacervation, though highly effective and achievable at the bench-scale, is challenging to scale-up because of the complexity and high-cost of the process. Thus, I developed a novel complex coacervation process (herein referred to as the ‘CoCo process’) that combines the coacervation, shell hardening and drying steps into one step by spray drying. During spray drying, the base vaporizes upon atomization, lowering the pH of the atomized droplets and inducing the two oppositely charged polymers to associate by complex coacervation. Rapid moisture removal force tightens associations between the polymers, leading to formation of water-insoluble microcapsules that are collected at the outlet of the spray dryer. The CoCo process overcomes the commercialization barrier and appears as a promising technique to encapsulate various cargo for a wide range of applications. This work investigated how to control the barrier properties of matrix microcapsules formed by the CoCo process to stabilize the bioactive components and control the release of the bioactive components for various applications. First, as a proof concept, the potential of the CoCo process to encapsulate volatile oil was investigated by encapsulating D-limonene using gelatin and alginate as matrix building components, and succinic acid and a volatile base in the formulations to modulate the pH. Here I defined a metric termed as the extent of complex coacervation (ECC) to assess the extent to which all polymers within the particles participate in complex coacervation and it was defined as the fraction of polymers that do not solubilize from the CoCo particles when the spray dried powders are suspended in water. Insoluble CoCo particles were produced without chemical cross-linking, with extent of complex coacervatio