Citric acid esterification of rice starches from different sources for stabilizing Pickering emulsions

Natural starch particles are potential candidates as stabilizers in Pickering emulsions. However, the good hydrophilicity of starch particles makes them difficult to be adsorbed on the oil-water interface of Pickering lotion, resulting in insufficient stability of lotion and limited application in food industry. Chemical modification is one of potential strategies to enhance the hydrophobicity of starch particles. In this work, indica rice starch (IRS), japonica rice starch (JRS), and waxy rice starch (WRS) were modified to improve the hydrophobicity by citric acid and used for stabilizing Pickering emulsions. The esterified starches were obtained by esterification between the starches and acid anhydride from the dehydration of citric acid at high temperature, indicated by the disrupted crystalline structure of starches and a collapsed and pitted surface resulted from aggregation of esterified starches with enhanced hydrophobicity. Meanwhile, the thermal decomposition temperature was reduced, and the hydration properties of esterified starches such as swelling property, gelatinization property and light transmittance were decreased. In particular, the esterification showed a more significant impact on the hydration properties of WRS. Furthermore, the esterification reduced the particle size of Pickering emulsions and improved the emulsion stability, and the esterified WRS showed higher stability. This work provides an alternative strategy for controlled preparation and application of food and biology of starch-based emulsion materials. • IRS, JRS and WRS were esterified by citric acid to induce the hydrophilicity. • The modification enhanced the hydrophobicity and disrupted crystalline structure. • Thermal decomposition temperature and hydration properties were induced. • Particle size of Pickering emulsion was reduced by modification starch. • The stability of Pickering emulsion was improved by esterification starch.