| Oil powder is commonly added to coffee or milk tea as a milk substitute in the beverage industry. Oil powders on the market own many shortcomings, such as the problem of poor dispersion degree in cold water. In order to develop high quality products, this paper has carried on the study of characteristics of oil powders, especially the dispersing properties in the cold water and its influence factors, discussing the properties of initial emulsion on powders after spray drying.The formula of this cold water dispersible oil powder were studied and the content of those components were determined by the design of experiment. The properties of this formula was investigated for its initial emulsion and oil powder analysis by characterization using emulsion droplet size and viscosity, solubility, particle size and encapsulation efficiency. The formula were finally determined by single factor experiments. Whey protein concentrate(WPC) and NL 100 were selected as wall materials, mass ratio of WPC to NL 100 were optimized to 3:2. An optimal formula was composed of 6%(w/w) whey protein and 4%(w/w) NL 100. As emulsifiers, sodium stearyl lactate(SSL) and distilled monoglyceride(DMG) were used up to 2.4%(w/w) of total concentration at a mass ratio of 1:2.The preparation process and conditions were optimized. The effect of p H and homogeneous pressure on emulsion stability and oxidation stability were investigated. The results showed that the mean emulsion droplet size was at the minimum value under neutral p H condition while the absolute value of Zeta potential reached at 42 m V. The emulsification system owned a certain static stability under neutral p H condition. The optimal homogeneous condition was 35 MPa twice and emulsion homogenized twice showed superior stability. Inlet air temperature and outlet air temperature was optimized by 180 °C and 85~90 °C, respectively. Solid content should be 30%. The solubility of this formula were up to 99%. The average volume-surface diameter(D3, 2) for the instant oil powder was 20~30 μm. The reconstituted emulsion size was 300 nm with a small polydispersity index(PDI). This cold water soluble oil powder owned a wide adaptability of p H, and can maintain a relatively stable system even in weak acid environment.Considering consumers’ nutrition consumption demands, high oleic sunflower oil(HOSO) were chosen to replace hydrogenated palm oil as core material. Further studies were carried out on the oxidation stability of oil powder. There is basically no change of the surface oil and fatty acid composition of HOSO oil powder during the storage time under 60 °C. HOSO oil powder was selected as a model to evaluate the oxidation speed. Taking POV as index, the oxidation kinetic equation of HOSO cold water dispersible oil powder was calculated. And the shelf life of this oil powders were suggested as 308 days on 25 °C, achieving the storage performance of commercial oil powders. A stable emulsion system can help core oil who owns high content of unsaturated fatty acid from oxidation in a certain extent, inhibiting lipid from oxidation.As to evaluate the overall properties of this cold water dispersible oil powder, this paper discussed the relationship between the structure of this newly oil powders and its physical properties. The glass transition temperature was above 65 °C measured by differential scanning calorimetry(DSC), which meant that the powder were under glassy state in the room temperature and this could be benificial to the storage. Infrared spectrum(FTIR) illustrated that there was an interaction between NL 100, WPC and the core oil. Microstructure was observed by scanning electron microscope. The surface of samples was smooth, existing no holes or fissures on the surface. The integrity of the surface implied that the microcapsules own superior protection and retention of the core material. The oil powder could be dissolved rapidly in cold water with no floating particles after little stirring, maintaining good stability after 24 h. Comparing to commercial oil powders, the sensory evaluation showed that the cold water dispersible oil powders owned better cold water dispersion and higher overall quality. |
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