Curcumin is an active polyphenolic compound with antioxidant, anti-inflammatory and antitumor properties. Curcumin, however, is highly unstable under physiological conditions due to its low stability in acidic and alkaline conditions. Therefore, the objective of this study was to investigate the effects of enzyme-treated rice starch as a wall material on the stability of curcumin in oil-in-water emulsion under different pH conditions. The rice starch was treated using 4-a-glucanotransferase for different time periods and their molecular weight distribution was measured by HPSEC. Curcumin was encapsulated within lipid droplets of O/W emulsion prepared with Tween 20 and the modified rice starch in the aqueous phase at different concentrations (0, 2.5, 7.5 and 10 wt%). The temperature and pH stability of the system were determined respectively by measuring particle size, zeta potential and retention of the curcumin loaded in the emulsion after one-week storage in the solutions with different pH and temperature conditions. The average molecular weight of the modified starch decreased with treatment time. The 96h treated rice starch had the lowest molecular weight while the 1h treated starch mainly consisted of high molecular weight components. The storage temperature did not significantly influence the stability of curcumin emulsion. However, the particle size of the emulsion with modified starch slightly increased when stored at acidic pH condition, which might be attributed to starch aggregation. The curcumin retention was higher for the samples with the modified starch than the control at all concentrations. The pH stability of the curcumin was also higher than the control at all pH conditions. Specifically, the 1h treated starch showed the best performance regarding curcumin protection in emulsion, which might be attributed to the high viscosity that retarded the curcumin release. Further research needs to be conducted on the mechanism.

• Hye Rin Park(Center for Food and Bioconvergence, Department of Biosystems and Biomaterials Science and Engineering Seoul National University)
• Shin-Joung Rho(Center for Food and Bioconvergence, Department of Biosystems and Biomaterials Science and Engineering Seoul National University)
• Yong-Ro Kim(Center for Food and Bioconvergence, Department of Biosystems and Biomaterials Science and Engineering Seoul National University)