β-carotene bilayer emulsions coated by milk proteins and chitosan–polyphenol conjugates

What is it about?

The objectives of the present study were to investigate the influence of chitosan–(–)-epigallocatechin-3-gallate (EGCG) conjugates on physicochemical properties of β-carotene emulsions coated by α-lactalbumin (LA) or sodium caseinate (SC). Covalent modification of chitosan with EGCG was achieved by hydroxyl–free radical grafting. Then based on layer-by-layer electrostatic deposition, β-carotene bilayer emulsions stabilized with different milk proteins and chitosan–EGCG conjugates (CEC) were prepared. The physicochemical properties of primary and secondary emulsions were mainly characterized by droplet size and distribution, zeta-potential, rheological behavior, transmission profiles using LUMiSizer and degradation of β-carotene in the emulsions during the storage. Besides, the effects of environmental stresses (ionic strength, freeze–thaw and thermal treatments) on physical stability of primary and secondary emulsions were evaluated. Data of droplet size and zeta potential indicated that cationic CEC were adsorbed on the droplet surfaces. Steady-state flow measurements revealed that the viscosity of primary emulsions could be enhanced by the adsorption of CEC. In addition, physical stability of SC-coated emulsion was improved by the adsorption of CEC, while the layer-by-layer electrostatic deposition hardly improved the stability of LA-stabilized emulsion in the absence or presence of environmental stresses. In comparison with the primary emulsions, the bilayer emulsions significantly improved chemical stability of β-carotene against heat treatment and ultraviolet (UV) light exposure, and the least degradation of β-carotene occurred in SC–CEC coated emulsion. In general, SC–CEC coated emulsion exhibited the best physicochemical properties among all emulsions studied in this research.

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Why is it important?

1. Bilayer emulsions were prepared using different milk proteins and chitosan–EGCG conjugates (CEC). 2. CEC formed thicker layers around oil droplets coated by sodium caseinate (SC). 3. CEC adsorption improved physical stability of SC-coated emulsion in the absence or presence of environmental stresses. 4. Bilayer β-carotene emulsions exhibited better chemical stability than monolayer ones. 5. SC–CEC stabilized emulsion had the best physicochemical properties among all emulsions.

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