This work was initiated to prepare proteinstabilized b-carotene nanodispersions using emulsificationevaporation. A pre-mix of the aqueous phase composed of a protein and hexane containing b-carotene was subjected to high-pressure homogenization using a microfluidizer. Hexane in the resulting emulsion was evaporated under reduced pressures, causing crystallization and precipitation of b-carotene inside the droplets and formation of b-carotene nanoparticles. Sodium caseinate (SC) was the most effective emulsifier among selected proteins in preparing the nanodispersion, with a monomodal b-carotene particlesize distribution and a 17-nm mean particle size. The results were confirmed by transmission-electron microscopy analysis. SC-stabilized nanodispersion also had considerably high f-potential (-27 mV at pH 7), suggesting that the nanodispersion was stable against particle aggregation. Increasing the SC concentration decreased the mean particle size and improved the polydispersity of the nanodispersions. Nanodispersions prepared with higher b-carotene concentrations and higher organic-phase ratios resulted in larger b-carotene particles. Although increased microfluidization pressure did not decrease particle size, it did improve the polydispersity of the nanodispersions. Repeating the microfluidization process at 140 MPa caused the nanodispersions to become polydisperse, indicating the loss of emulsifying capacity of SC due to protein denaturation.

This work demonstrated the preparation of protein-stabilized beta-carotene nanodispersions using the solvent displacement technique. The emulsifying performance of sodium caseinate (SC), whey protein concentrate (WPC), whey protein isolate (WPI), and a whey protein hydrolysate (WPH, 18% degree of hydrolysis) was compared in terms of particle size and zeta-potential of the nanodispersions. SC-stabilized nanodispersions exhibited a bimodal particle size distribution: large particles (stabilized by casein micelles) with a mean particle size of 171 nm and small particles (stabilized by casein submicelles) of 13 nm. This was confirmed with transmission electron microscopy analysis. Most of the beta-carotene precipitated (87.6%) was stabilized in the small particles. On the other hand, the nanodispersions stabilized by the whey proteins were polydispersed with larger mean particle sizes. The mean particle size of WPC and WPI was 1730 and 201 nm, respectively. The SC-stabilized nanodispersion was expected to be more stable as indicated by its higher absolute zeta-potential value (-31 mV) compared to that of WPC (-15 mV) and WPI (-16 mV). Partially hydrolyzed whey protein possessed improved emulsifying properties as shown by WPH-stabilized samples. It was interesting to note that increasing the SC concentration from 0.05 to 0.5 wt % increased the particle size of beta-carotene stabilized by casein micelles, while the reverse was true for those stabilized by SC submicelles. Microfluidization at 100 MPa of SC solution dissociated the casein micelles, resulting in a decrease in mean particle size of the casein micelle-stabilized particles when the SC solution was used to prepare nanodispersions. The results from this work showed that protein-stabilized beta-carotene nanodispersions could be prepared using the solvent displacement technique.

BACKGROUND: Milk proteins are used in a wide range of formulated food emulsions. The stability of food emulsions depends on their ingredients and processing conditions. In this work, β-carotene nanodispersions were prepared with selected milk-protein products using solvent-displacement method. The objective of this work was to evaluate the stability of these nanodispersions against heating, salts and pH.

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