Double emulsions for iron encapsulation: is a high concentration of lipophilic emulsifier ideal for physical and chemical stability?

BACKGROUND: Worldwide iron deficiency in diets has led to a growing interest in the development of food‐compatible encapsulation systems for soluble iron, which are able to prevent iron's undesirable off‐taste and pro‐oxidant activity. Here, we explore the use of double emulsions for this purpose, and in particular, how the lipophilic emulsifier (polyglycerol polyricinoleate, PGPR) concentration influences the physicochemical stability of water‐in‐oil‐in‐water (W(1)/O/W(2)) double emulsions containing ferrous sulphate in the inner water droplets. Double emulsions were prepared with sunflower oil containing 10 to 70 g kg(−1) PGPR in the oil phase, and were monitored for droplet size distribution, morphology, encapsulation efficiency (EE) and oxidative stability over time. RESULTS: Fresh double emulsions showed an initial EE higher than 88%, but EE decreased upon storage, which occurred particularly fast and to a high extent in the emulsions prepared with low PGPR concentrations. All double emulsions underwent lipid oxidation, in particular those with the highest PGPR concentration, which could be due to the small inner droplet size and thus promoted contact between oil and the internal water phase. CONCLUSION: These results show that a too high PGPR concentration is not needed, and sometimes even adverse, when developing double emulsions as iron encapsulation systems. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.