Soy protein nanoemulsions improve stability and bioavailability of vitamin D

BACKGROUND Deficiency and insufficiency of vitamin D (VD) afflicts populations worldwide. Fortification of foods with VD has been present for decades; however, its stability in foods is often compromised by its rapid degradation, low absorption and poor water solubility. In this study, soy protein isolate was conditioned using pH shifting and ultrasound treatment to create soy protein‐based nanoemulsions (SPNEs). The objective was to evaluate the stability, bioaccessibility and bioavailability of VD dispersed in SPNEs. METHODS SPNEs were prepared by mixing canola oil (1%, w/w) and soluble SPI (30 mg/mL) containing VD (100 μg/mL; cholecalciferol) and sonicating (20 kHz) 5 min. VD‐containing SPNEs were compared to controls including VD dispersed in water after sonication and in lecithin with canola oil after sonication. VD‐containing SPNEs were freeze dried and evaluated after resuspension. Particle size was measured using dynamic light scattering spectroscopy. VD stability was evaluated after UVB light exposure for 0, 30, 60 and 120 min followed by quantification using and reversed phase HPLC‐UV. Bioaccessibility was evaluated in a two‐compartment in vitro digestion model. Bioavailability was evaluated in adult Long‐Evans hooded rats. Rats were conditioned for a week under a AIN‐93M diet before receiving a gavage dose of: 1) VD‐containing SPNEs (2 mL, 150 μg/mL), 2) Oil with VD (0.5 mL, 300 μg/mL), and 3) Oil without VD (0.6 mL canola oil). After gavage, specific groups of animals (n=3–5) within each treatment were euthanized at 1, 9, 24, and 48 hours after oral dose. Serum 25(OH) VD levels in rats were measured post‐mortem using a colorimetric (450 nm) sandwich ELISA. RESULTS Soy nanoparticles (15–30 nm) were larger ( p <0.05) than VD‐containing SPNEs (10–20 nm). VD‐containing SPNEs had higher particle size after freeze drying (50–70 nm; p <0.05). Recovery of VD after 60 min UV exposure was 52.3%, 12.8%, and 9.8% in SPNEs, emulsified in lecithin, or without emulsifier in water, respectively. VD bioaccessibility was higher ( p <0.05) in SPNEs (96%) than emulsified in lecithin (69%), or without emulsifier in water (63%). Pharmacokinetic studies in rats showed that oral delivery of VD in SPNEs resulted in 8.1‐fold increase in the AUC (p<0.05) and reaching a Cmax at 24 hours compared to the Oil with VD control. These results revealed that dispersion of VD in SPNEs protects VD from UV exposure and increases its bioaccessibility and oral bioavailability. Future studies will evaluate the sensory properties of SPNEs in food products. Support or Funding Information University of Illinois at Urbana‐Champaign, King Saud University