Formation of nanoemulsion - based delivery systems for liposoluble vitamins: stability assessment and digestion studies

Liposoluble vitamins are the biological active micronutrients which have health promoting effects. They may possess poor chemical stability, poor water solubility and low bioavailability. Therefore it is required to design effective delivery systems to incorporate these bioactives into functional food and beverage products. Nanoemulsion-based vitamin delivery systems were aimed to be produced using natural emulsifiers: lecithin, quillaja saponin, whey protein isolate (WPI) and gum arabic (GA) in a high pressure homogenizer. The effect of nanoemulsion composition and environmental stresses (pH, ionic strength and temperature) on the mean particle diameter and zeta-potential of the delivery systems were investigated and the stability was assessed by referring to theoretical phenomena. Simulated gastrointesinal system was used to evaluate the influence of carrier oil type on the digestion and bioaccessability of the vitamin D3. The mean particle diameter had a minimum value at an intermediate vitamin E-to-orange oil ratio in the oil phase: d32= 0.13µm for lecithin and 0.12µm for quillaja saponin at 50% vitamin E. WPI (d32 = 0.11 μm, 1% emulsifier) was better than GA (d32 = 0.38 μm, 10% emulsifier) at producing small droplets at low emulsifier concentrations. Quillaja saponin and lecithin formed stable nanoemulsions at pH 3-8, however the loss of electrostatic repulsion caused instability at pH 2. Higher salt concentrations >100 mM NaCl for lecithin and ≥ 400 mM NaCl for quillaja saponin caused instability due to the electrostatic screening. All the sytems were stable at temperatures from 30 to 90 °C. WPI-stabilized nanoemulsions were unstable to flocculation at pH 5, at high ionic strength (>100 mM), and at elevated temperatures (>60 °C), whereas GA-stabilized emulsions were stable. The rate of free fatty acid release during lipid digestion decreased in the following order: medium chain triglycerides (MCT) > corn oil ≈ fish oil > orange oil > mineral oil. Long chain triglycerides were the most effective at increasing vitamin D3 bioaccessibility. These results provide useful information about the emulsifying and stabilizing capacities of natural emulsifiers for forming food-grade vitamin-enriched delivery systems.