Phycocyanin-rich water-in-oil-in-water (W1/O/W2) double emulsion with nanosized particles: Improved color stability against light exposure

Acidic environments and light exposure have been known to have detrimental effects on phycocyanin (PC), a spirulina-derived chromoprotein popular among food and pharmaceutical manufacturers. We developed a water-in-oil-in-water (W1/O/W2) double emulsion system for mitigating the discoloration and precipitation issues of PC at pH 3.0 and under light exposure. The nanostructured (∼170 nm) W1/O/W2 emulsion droplets were obtained under the combined efficacy of multiple stabilizing components. Glycerol (40 wt%) in the internal aqueous phase acted as both the protein stabilizer and thickener. Fine droplet size, optical clearness, and thermodynamic stability were obtained using polyglycerol polyricinoleate (PGPR, 4 wt%) as the lipophilic emulsifier and Tween 20 (8 wt%) as the hydrophilic emulsifier. The mechanical robustness of droplets withstood multiple emulsification steps by high pressure homogenization, an efficient, high energy technology amenable to industrial-scale productions. Lipid oxidation was suppressed by using medium-chain triglyceride coconut oil and multiple antioxidants, which offered photoprotection on the encapsulated PC against oxidative damage induced by UV irradiation. The optimized PC-rich W1/O/W2 emulsion exhibited high PC loading capacity and long-term physical stability without leakage, phase separation, and retained the vivid blue color with only slight turbidity. Overall, our PC-rich W1/O/W2 double emulsion system demonstrated good thermodynamical, mechanical, and photooxidative stabilities against the acidic and light storage conditions that are commonly used during food processing, making PC a widely applicable natural colorant and protein source in foods.