Zhanqun Hou

Investigation into the physicochemical stability and rheological properties of β-carotene emulsion stabilized by soybean soluble polysaccharides and chitosan.

In this study, the possibility of producing stable O/W emulsions incorporating beta-carotene in oil droplets surrounded by multiple-layer interfacial membranes has been demonstrated. Emulsions were prepared using a two-stage process by homogenization, which relied on the adsorption of chitosan to anionic droplets coated with soybean soluble polysaccharides (SSPS). Results showed that the zeta-potential, particle size, and rheological properties of emulsions were greatly dependent on the chitosan concentration. The electrical charge on the droplets increased from -34 to 58.2 mV as the chitosan concentration was increased from 0 to 2 wt %, which indicated that chitosan adsorbed to the droplet surfaces. The mean particle diameter of the emulsions increased dramatically with the rise of chitosan concentration from 0 to 0.33 wt %, indicating the formation of large aggregated structures. At chitosan concentrations above 0.33 wt %, the mean particle diameter of emulsions decreased and reached a minimum value of 0.79 mum at a chitosan concentration of 0.5 wt %. Dynamic oscillatory shear tests indicated that the viscoelastic behavior could be enhanced by the adsorption of chitosan onto the SSPS-coated droplet surfaces. Chitosan concentration had a significant (p < 0.05) impact on the stability of beta-carotene. The least degradation occurred in the emulsion with chitosan concentration of 0.5%. These results implied that the physicochemical stability of beta-carotene emulsions has been improved by the adsorption of chitosan.

The Effect of Whey Protein Isolate-Dextran Conjugates on the Freeze-Thaw Stability of Oil-in-Water Emulsions

This study examines the impact of Maillard-type conjugates formed between whey protein isolate (WPI) and the nonionic polysaccharide dextran by dry heating at 80°C for 2 hours (conjugate 1) and at 60°C for 5 days (conjugate 2) on the freeze-thaw stability of oil-in-water emulsions. Emulsions stabilized with WPI, WPI-dextran mixture, conjugates 1 and 2, were prepared using microfluidizer, respectively, and then subjected to from one to three freeze-thaw cycles (−18°C for 22 hours, +40°C for 2 hours). The emulsion stability to freeze-thaw processing was assessed by zeta potential, average particle size, polydispersity index (PDI) and backscattering profile by a recently developed optical analyzer (Turbiscan). Results demonstrated that WPI-dextran conjugates brought about a remarkable improvement in freeze-thaw stabilizing properties when compared with WPI or WPI-dextran mixture which can be attributed to the enhancement of repulsive steric forces between the oil droplets as a result of dextran overlapping the thicker interfacial coatings surrounding the oil droplets. The conjugate 2 stabilized emulsion showed much better stability after freeze-thaw cycling than the conjugate 1 probably due to the higher extent of conjugation.

Stability of β-Carotene in Oil-in-Water Emulsions Prepared by Mixed Layer and Bilayer of Whey Protein Isolate and Beet Pectin

The addition order of mixed layers of protein and polysaccharide on oil-water interface has been shown to influence physical stability of the emulsion, but little is known about how it impacts chemical stability. Therefore, this study investigated differences in the chemical stability of oil-in-water (O/W) emulsions containing β-carotene droplets coated by whey protein isolate (WPI)-beet pectin through direct preformed mixture (mixed emulsion) and consecutive layer-after-layer (bilayer emulsion) at pH 4.0 and 7.0. The results clearly indicated that both forms of β-carotene emulsions exhibited nearly identical degradation profiles during storage at 55°C. The stability of β-carotene in O/W emulsions could be significantly improved by the addition of iron chelator desferroxamine for both mixed and bilayer emulsions at pH 4.0, but not at pH 7.0. The addition of α-tocopherol could also significantly inhibit the β-carotene degradation for both emulsions at pH 4.0 and 7.0. However, the difference of the improved β-carotene stability between the mixed and bilayer emulsions was not significant. These results implied that the protein-polysaccharide adsorption approach in the β-carotene droplet surface did not play a major role in the degradation rate of β-carotene in O/W emulsions, and it was possible to produce emulsions through mixed and bilayer methods with the similar chemical stability of active compounds for use in a variety of food products.