Consumption of carotenoids may reduce the risk of certain chronic diseases, but their use in foods is currently limited because of their low bioavailability and physicochemical instability. The purpose of this research was to evaluate the physical stability of β-carotene (β-CE) in oil-in-water sodium caseinate nanoemulsion under the conditions of pH, temperature, ion strength and storage time. β-CE nanoemulsion is liable to aggregation at pH values close to the isoelectric point of the casein (pH 4–5). The β-CE nanoemulsion shows preferable physical stability under the conditions of heat at 80 °C for 90 min and ion strength (100–500 mmol/L). The physical stability of nanoemulsion in digestion model was also evaluated.Confocal images as well as droplet characterization in terms of size and charge indicate that the negative charge and Z-average of droplet size in different digestion stages are variant. β-CE nanoemulsion became highly aggregated when exposed to gastric condition. The extent of the FFA release is increased with the increase of lipolysis time. These results have significant implications for using proteins to fabricate emulsion-based delivery system for β-CE.

The characterization and bioaccessibility of β-carotene (β-CE) in re-assembled casein (CN) were investigated in this study. At pH 4.6, β-CE in re-assembled CN significantly lowered the zeta-potential to a negative value compared to that of CN. The morphology of β-CE in re-assembled CN was characterized by atomic force microscopy. β-CE in re-assembled CN exhibited a more uniform and homogenous dispersion, with peak-to-valley differences of 6.8 nm rather than 91.3 nm for the pure β-CE. β-CE in re-assembled CN can effectively protect β-CE against degradation under conditions of heat and ultraviolet radiation. The antioxidant activity of β-CE when it was encapsulated in re-assembled CN was significantly higher than β-CE in control samples under both experimental conditions. The total release rate of β-CE was 76.7% and 63.4% by trypsin and pepsin hydrolysis, respectively. These results indicated a feasible application in the food industry.

The effect of the heat-induced whey proteins/κ-casein complex on the acid gelation of yak milk was investigated. Both soluble whey protein/κ-casein complexes and the surface as micelle-bound complexes change the rheological properties of yoghurt. However, the soluble whey protein/κ-casein complexes were predominant in increasing the storage modulus (G′), water-holding capacity and firmness of acid gelation than micelle-bound complexes. The water-holding capacity and firmness increased with the increase of the amount of the soluble whey protein/κ-casein complexes. The water holding capacity and firmness of yoghurt from heated yak milk at pH 7.0 was higher than that at pH 6.6 and pH 7.4. The result also indicated that the amount of soluble heat-induced whey protein/κ-casein complexes were predominant in increasing the water holding capacity and firmness of yoghurt than the micelle-bound protein complexes.