Biological Stability and Delivery Studies to Elucidate the Role of Thickener Solid Particles on Water-in-Oil Emulsion Containing Microalgae

The main goal of this dissertation was to study and modify water-in-oil (W/O) emulsions to obtain a predictable storage and delivery system for algae. Water-in-oil emulsions were prepared with different concentrations of the following three thickeners in the oil phase: Aerosil R974 (silica nanoparticles), Bentone 38 (hectorite clay), and Bentone 150 (Bentonite clay). Room temperature storage stability and cell viability in emulsions were measured. Emulsions prepared with different thickeners did not experience cell death up to 340 days of storage. Emulsions containing different concentrations of thickener did not show a statistical difference in cell viability up to 305 days of storage. Emulsions with different thickeners were physically stable likely due to the formation of stable networks in the oil phase and increase in stabilization of the water--oil interface facilitated by the thickeners. Physical stability (prevention of algae settling and clumping) of the emulsions led to biological stability of the algae. Release rate of the aqueous internal phase of W/O emulsions was determined for emulsions containing different thickeners in the oil phase.;Release rate was measured by adding fluorescent Brilliant Sulfaflavine (BSF) in the aqueous phase of the emulsion. Emulsions containing 0.5wt% thickener in the oil phase were sprayed into plastic tubs. Maximum release of the internal phase of the emulsion containing BSF was observed within 8 hours of application. For emulsions containing BSF, Bentone 150 had the highest release rate after 30 minutes of application followed by Bentone 38, Aerosil R974, and finally emulsions without thickener. Release rates of algae from emulsions formulated with different thickeners and no thickener were not statistically different. Recovery of the internal phase containing BSF from the emulsion was done using the drop method (average droplet size equals ∼2mm), which has been used to determine cell viability in emulsions during storage. It was determined that this method has a very low percent recovery of the internal phase indicating that the creation of more surface area in the form of small drops, such as those created by spray equipment, is necessary to have a higher release rate of the internal phase. The release rate from the W/O emulsion was significantly improved when the formulation was sprayed (average droplet size equals ∼45microm). Emulsions sprayed into containers with N-8 growth media released enough cells to serve as inoculum for a successful growth culture. The data support the use of W/O emulsions as a seed technology for algae cultivation.;Successful cell storage technologies must maintain cell viability and physical stability for extended periods of time under varying temperatures. In addition to understanding how physical and biological stability are influenced by storage temperature, it is important to determine if the emulsion provides protection to cells upon extended exposure to lethal temperatures. Emulsions containing Chlorella sorokiniana and Chlorella minutissima were formulated with different thickeners (silica nanoparticles and Bentone 38) in the oil phase and cell viability at high temperatures was compared to unformulated cell suspensions. Emulsions provided Chlorella sorokiniana protection to exposure to 42°C after 24 hours. Emulsions containing silica nanoparticles showed prolonged temperature protection after 72 hours. At 46.5°C cell inactivation was greater for cells in cell suspension and in emulsions formulated with Bentone 38 compared to emulsions formulated with silica. Cell suspension containing Chlorella minutissima had a faster inactivation constant at 38°C and 42°C compared to emulsions containing silica nanoparticles and Bentone 38. At 38°C cells in emulsions containing silica nanoparticles had slower death rates and they were less susceptible to heat over time. At 42°C after 8 hours of heat exposure, emulsions formulated with silica nanoparticles showed a notable protection against cell inactivation. (Abstract shortened by UMI.).