Chapter 1. Emulsifying properties of heat-treated octenyl succinyl starch
Starch can be modified by treating it with octenyl succinic anhydride (OSA). Such modified starch finds applications as emulsifiers in food emulsion systems. In spite of there being several studies on the properties of emulsions stabilized by OSA-starch, a great deal of fundamental information on the emulsifying properties of OSA-starch is still unknown. In the present study, we present the emulsifying properties of heat-treated OSA-starch. First, we prepared the aqueous suspension of OSA-starch at 80℃. We then premixed the solution with oil using Silverson blender at 8000 rpm for 15 min, followed by homogenization using Microfludizer at 3000 psi (two passes) to prepare OSA-starch emulsions. In the 0.5 % OSA-starch emulsions, fat globule size(d32) was found to be much smaller in emulsions with increase in OSA-starch concentrations(0.1%:1.58 μm→ 1.25 %: 0.31 μm). Mass of adsorbed OSA-starch at oil droplets(Surface load) was increased with concentration of OSA-starch in range from 0.2 to 1.25 %. As for creaming stability, heat-treated OSA-starch emulsions were fairly stable over 0.5 % OSA-starch. However, such emulsions showed some instability caused by pH (<6), suggesting that electrostatic stabilizing mechanism was working to some extent. These results agreed with changes in zeta-potential data with pH. The droplet sizes of 0.5 % OSA-starch were influenced by pH(pH 3: 1.57 μm, pH 5: 0.59 μm, pH 7: 0.28 μm, pH 9: 0.27 μm). Confocal laser scanning microscope was carried out to observe the interfacial layer. OSA-starch surrounded oil droplets and made thick interfacial layer(layer thickness: 0.89 μm). This suggested that heat-treated OSA-starch acted as polymeric emulsifier and formed steric film. In conclusion, OSA-starch was more effective as an emulsifier when heat-treated.
Chapter 2. Properties of octenyl succinyl starch nanoemulsions
In this present study, we carried out the effect of OSA-starch concentrations, homogenization pressures and co-surfactant concentrations on properties of nanoemulsions. especially, we focused on retarding ostwald ripening because we used MCT oil: It is more soluble with water than conventionally used oil(e.g., soybean oil, canola oil etc.). First, we prepared OSA-starch(0.5-2%) nanoemulsions with co-surfactants(0.5-3%) via microfludizer(5,000-20,000 psi). And then, droplet size in nanoemulsions was measured by Nano ZS(Malvern instrument, UK) for 4 weeks. Turbiscan was also used to investigate the creaming stability for 72 hours. Droplet sizes were decreased with increasing in concentration of OSA-starch and homogenization pressures(0.5%: 237.1 nm→2%: 207.2 nm; 5,000 psi: 247.3 nm→20,000 psi: 207.2 nm). As for 2% OSA-starch nanoemulsion with co-surfactants, droplet sizes were decrease with increasing in concentration of co-surfactants(Almax3800=0.5%: 262.5 nm→3%: 209.0 nm; Lecithin=0.5%: 831.3 nm→3%: 152.2 nm). Creaming stability was fairly stable in 2% OSA-starch nanoemulsions with 2-3% co-surfactants. This suggested that Ostwald ripening was occurred in OSA-starch nanoemulsions with MCT oil and retarded by adding co-surfactants, especially, using lecithin.