Design and characterization of novel O/W/O double emulsions

In this study oil-in-water-in-oil (O/W/O) systems which can be called double emulsion (DE) were formulated by using biopolymers. To formulate DE, first oil was dispersed in water. This process is referred oil-in-water O/W emulsion, then this emulsion was dispersed in a second oil phase. As they are more complicated to produce and more susceptible to breakdown there are only a few published researches about O/W/O systems. In this research O/W/O DEs were designed by fat crystallization method in a two stage emulsification method; in the first step primary emulsion (PE) was formulated which stabilized with biopolymers, and in the second step hardstock was added to the PE to get a structured oil system. Consequently, biopolymers were used to stabilize oil-in-water (O/W) emulsions and these emulsions were used further as template to generate the O/W/O emulsion with low solid fat content. Specific objectives were; to formulate O/W/O DEs at different proportion of liquid oil, hardstock, water and to characterize them in terms of microscopic structure, droplet size distribution, rheology, texture and thermal stability. A new approach was investigated that use of less solid fat in converting liquid oil into internal water droplets to get similar structure. Initially, sunflower oil (SFO) was dispersed in stock solutions containing gelatin (GL) at 10 weight% (wt) and xanthan gum (XG) at 2 wt% to develop PE. Three PEs at the oil/water ratio of 6:4 (I), 2:8 (II) and 1:9 (III) were prepared by using a high-energy dispersing unit Ultraturrax. For the DE preperation step, O/W ratio of 6:4 (I) emulsion was used in the first process. Varying amounts of palm oil (melted at 50 ˚C) and SFO added to 6:4 PE (I) then mixture homogenized with Ultraturrax. Emulsions containing SFO at 30 wt% (IV), 38.3 wt% (V), 46.7 wt% (VI) and 55 wt% (VII) were obtained while cooling them at -0.15 ˚C after two minutes of homogenization. In this way, fat crystallization occured and DE formation was observed. For next process, DEs prepared from 2:8 O/W ratio of (II) PE. Different amount of palm oils was directly added to PEs and mixture was subjected to cooling at -0.15 ˚C during homogenizing. As a result, DEs at 30 wt% (VIII), 40wt% (IX) and 45 wt% (X) water were obtained just by using natural emulsifier (GL) and stabilizer (XG). For achieving DE at 60 wt% (XI) water a lipophilic surface active agent polyglycerol-polyricinoleate was used at 0.4 wt%. For the last process 6:4 O/W ratio of PE (I) was used but water concentration varied at 20 wt% (XII) and 26.67 wt% (XIII).The microstructures of these systems were recorded by optical microscopy and cryogenic scanning electron microscopy. Microscopic images revealed the morphology of emulsions. Oil droplets and internal water droplets in emulsions can clearly be seen under polarized light and normal light. The light scattering method by Mastersizer was used to determine the average volume weighted droplet size of PEs. Droplet sizes measured as 9.22 ± 2.29 μm (I), 17.21 ± 1.05 μm (II), 16.89 ± 0.63 μm (III) respectively. Pulsed field gradient nuclear magnetic resonance (Pfg-NMR) was used to measure water droplet size of DEs. Droplet sizes measured as 8.91 ± 0.51 μm (Δ=36 second) and 10.23 ± 0.07 μm (Δ=66 second). The effect of different SFO concentrations (at 20 wt% water) and different water concentrations (at 20%, 26.67 wt%, 30 wt%, 40 wt%, 45 wt%, 60 wt% water) on the rheological and textural characteristics of emulsions were also evaluated using rheometer and texture analyzer to understand these systems. Texture analyses confirmed that hardness values decreased proportionally to the increasing SFO content from 30 wt% to 55 wt% at constant water ratio. Hardness values measured as 13.40 ± 1.68 N (IV), 9.70 ± 2.13 N (V), 8.12 ± 0.70 N (VI), 3.42 ± 0.61 N (VII) respectively. By increasing water content from 20 wt% to 60%, hardness values were also decreased. At different water concentrations hardness values were 58.99 ± 6.45 N (VIII), 27.47 ± 4.43 N (IX), 39.04 ± 2.13 N (X), 6.32 ± 0.67 N (XI). However, hardness values did not show major difference at 20 wt% and 26.67 wt% water. Amplitude sweep stress and frequency sweep tests were applied to understand viscoelastic behavior of emulsions. DEs showed weak gel structure and elastic behavior. Gel stiffness decreased by increasing water ratio which means that rheological results were in agreement with the results from texture analysis. Differential Scanning Calorimetry (DSC) was used to determine peak temperatures and heat absorption (melting) of samples. Thermograms confirmed that palm oil solidified during DE formation. DE samples stored in certain periods at 4 ˚C and recorded by optical microscopy. DE structure was still provided but water phase started to broke and emulsion stability decreased. The results of this work showed that the encapsulation of SFO by using GL and XG could be significant for producing reduced-fat products. Additionally, the optimization and the formulation of DEs with this method could be further used as a template for the encapsulation of flavors or other components.