**3.2. Physical stability of lutein emulsions prepared with bovine casein/lecithin and caprine casein/lecithin as emulsifiers**

In order to understand the effects of bovine casein or caprine casein in combination with phospholipids i.e., soybean lecithin on the chemical degradation of lutein, three sets of emulsions with corn oil were made. The three sets were stabilized by bovine casein/lecithin, caprine αs1-I-casein/lecithin, or caprine αs1-II-casein/lecithin. The mean particle diameters of oil droplets in the lutein-enriched emulsions stabilized by bovine casein/lecithin or caprine casein/lecithin ranged from 205.6 ± 2.3 to 208.9 ± 2.5 nm at pH 7.0 (**Table 1**). We observed no significant differences (p > 0.05) in the particle sizes of oil droplets in lutein-enriched emulsions with either bovine casein or caprine caseins during 0 and 7 days of storage at 21 ± 1°C.

The zeta potentials of the casein/lecithin-coated oil droplets in the lutein-enriched emulsions were negative at pH 7.0 (**Table 2**). The zeta potentials of the oil droplets in the luteinenriched emulsions prepared with the two caprine casein/lecithin emulsifiers were not different (p > 0.05), showing mean values of −36.8 ± 1.8 mV for caprine αs1-I-casein/lecithin and −35.9 ± 1.9 mV for caprine αs1-II-casein/lecithin, respectively. The lower zeta potentials of the oil droplets in the lutein-enriched emulsions stabilized by the two caprine casein/lecithin emulsifiers compared to the lutein-enriched emulsions stabilized by bovine casein/lecithin emulsifier can imply a decreased 'net' negative charge [25]. Differences in the amino acids of side chains of κ-, αs - and β-casein fractions in caprine whole caseins, where the less charged β-casein quantitatively dominates, could lead to less repulsive charge-charge interactions and this phenomenon can possibly explains why caprine caseins have lower zeta potentials (**Table 2**). On the basis of these findings, we can conclude that the lutein-enriched emulsions prepared with bovine casein/lecithin emulsifier and the two caprine casein/lecithin emulsifiers exhibited relatively good physical stability [13].

lecithin (**Figure 1**). The bovine casein/lecithin means on the bars are significantly different than the two caprine casein/lecithin means (p < 0.05) until four days of storage at 5°C (**Figure 1A**); the same tendency in lutein loss was observed during storage at 15°C (**Figure 1B**). Comparing the results of the two caprine casein/lecithin emulsifiers, the caprine αs1-II/lecithin emulsifier overall showed lower means than caprine αs1-I/lecithin emulsifier in both storage temperatures. In general, lutein degradation was faster in emulsions prepared with bovine casein/lecithin emulsifier than with the other two emulsifiers within 7 days of storage at 5 and 15°C (**Figure 1A** and **B**, respectively). The fact that lutein degradation was faster in the emulsions prepared with bovine casein/lecithin emulsifier compared to the emulsions prepared with caprine αs1-I-casein /lecithin emulsifier or caprine αs1-II-casein/lecithin emulsifier suggests that the interfacial layer formed by bovine casein/lecithin emulsifier was less efficient in protecting emulsified lutein against chemical degradation during storage at 5 and 15°C. The combination of caprine αs1-I-casein or caprine αs1-II-casein with soybean lecithin as emulsifiers resulted in a more favorable thickness of the interfacial layer thereby, slowing down the lutein degradation in these emulsions. This confirms that caprine caseins, which are 'rich' in their content of β-casein, formed a denser interfacial layer surrounding oil droplets and the possible role that the thickness of the interfacial layer played in the degradation of emulsified lutein. Furthermore, soybean lecithin, which is comprised of charged phospholipids such as phosphatidylinositol and phosphatidic acid [26], is more soluble in water and therefore, more easily absorbed at the oil-in-water interface thereby,

**Figure 1.** Lutein degradation in corn oil-in-water emulsions (pH 7.0) stabilized by bovine casein/lecithin, caprine (αs1-I) casein/lecithin or caprine (αs1-II)-casein/lecithin at 5°C (A) and 15°C (B) as a function of storage time. Values represent

Lutein-Enriched Emulsion-Based Delivery System: Impact of Casein-Phospholipid Emulsifiers…

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The stabilizing role of phospholipids in emulsions is important in the absorption of lutein by the host. From the nutritional point of view consumption of a lutein-enriched beverage emulsion stabilized by bovine casein/lecithin emulsifier or caprine casein/lecithin emulsifier will be a valuable means to counterbalance the deficiency in consumption of fruits and vegetables; this approach will reduce the negative effects of lower ingestion of health-promoting carotenoids. Overall, these results indicate that a high chemical stability of lutein in corn oil-inwater emulsions can be achieved by altering the physical properties of the emulsion droplet

producing a thicker interfacial layer protecting lutein.

**4. Conclusions**

the mean of three trials.
