α-lactalbumin enhancing emulsion stability of β-carotene

Abstract: β-carotene is the major carotenoid in carrots and the most widely studied natural carotenoid. It is very import in foods, for it adds the color to the food products, and also associates with human health. For example, it is the most potent precursor of vitamin A and has a potent antioxidant capacity. It also can lower the risk of heart diseases and certain types of cancers. However, the utilization of β-carotene as a nutraceutical ingredient in the food industry is currently limited because of its poor water-solubility, high melting point, low chemical stability and bioavailability. Oil-in-water emulsions are often a better choice for delivering β-carotene into functional foods since the emulsions increase bioavailability. One factor which can influence β-carotene stability in oil-in-water emulsions is the chemical and physical properties of the interface formed between oil and water, as some researchers reported protein has a positive effect on the degradation of β-carotene in oil-in-water emulsion. In this research, we used α-lactalbumin (α-LA) as emulsifier to stabilize nanoemulsion to deliver β-carotene. The effects of α-LA on the particle size, the zeta-potential, the encapsulation rate, the oil-water interfacial α-LA concentration, and the physical and chemical stability of β-carotene emulsion were determined. The mean particle diameter (Z-average) and zeta-potential of β-carotene emulsion were measured using the laser particle size analyzer (Malvern Instruments Ltd.) based on the dynamic light scattering principle. The particle size decreased and the zeta-potential increased with the increasing of the added amount of α-LA in β-carotene emulsion; but they did not change significantly (P>0.05) after adding more than 1.50% α-LA as the emulsifier. Adding more α-LA (0.25%-1.50%), the encapsulation rate was improved in a dose-dependent manner (P<0.05), however, there was no significant difference in the encapsulation rate when more than 1.50% α-LA was added in β-carotene emulsion. We used Turbiscan Lab Expert to evaluate the physical stability of β-carotene emulsion. Turbiscan stability index (TSI) of the top part of β-carotene emulsion was determined. TSI decreased with the increasing of the amount of added α-LA. When the addition of α-LA was more than 1.50%, there was no change in TSI, which meant the physical stability of β-carotene emulsion had become good. To remove continuous phase α-LA in β-carotene emulsion, we used the ultra high speed centrifuge to separate the oil phase and aqueous phase. The interfacial α-LA concentration increased significantly with the increasing addition of α-LA (P<0.05). There was multilayered α-LA on the interface between oil and water. This could explain the change of particle size, zeta-potential, encapsulation rate and TSI of β-carotene emulsion with the increasing addition of α-LA. β-carotene concentrations in emulsion samples were analyzed through the whole storage time. With less α-LA (0.25%-0.75%) the more degradation of β-carotene was observed during the storage under 55 ℃. The chemical stability of β-carotene was improved when more than 1.00% α-LA was added as the emulsifier in β-carotene emulsion. These results show that α-LA can be a kind of good emulsifier and the proper amount of addition is 1.50% in β-carotene emulsion. This study can be helpful to increase β-carotene utilization in food industry.