Food-grade microemulsions, nanoemulsions and emulsions: Fabrication from sucrose monopalmitate & lemon oil

Sucrose monopalmitate (SMP) is a non-toxic, biodegradable, non-ionic surfactant suitable for use in foods and beverages. This study aimed to establish conditions where stable microemulsions, nanoemulsions or emulsions could be fabricated using SMP as a surfactant and lemon oil as an oil phase. Emulsions (r > 100 nm) or nanoemulsions (r < 100 nm) were formed at low surfactant-to-oil ratios (SOR < 1) depending on homogenization conditions, whereas microemulsions (r < 10 nm) were formed at higher ratios (SOR > 1). The impact of simple mixing, thermal treatment, and homogenization on the formation of the different colloidal systems was investigated. Blending/heating was needed to produce microemulsions or emulsions, whereas blending/heating/homogenization was needed to produce nanoemulsions. The impact of environmental stresses (pH, ionic strength, temperature) on the functional performance of nanoemulsions and microemulsions was examined. Relatively stable nanoemulsions could be formed at pH 6 and 7 and stable microemulsions at pH 5 and 6, but extensive particle growth/aggregation occurred at lower and higher pH values. Microemulsions were relatively stable to salt addition (0-200 mM NaCl), but nanoemulsions exhibited droplet aggregation/growth at >= 50 mM NaCl after 1 month storage at pH 7. Microemulsions formed gels at low temperatures (5 degrees C), were stable at ambient temperatures (23 degrees C), and exhibited particle growth at elevated temperatures (40 degrees C). Nanoemulsions were stable at refrigerator (5 degrees C) and ambient (23 degrees C) temperatures, but exhibited coalescence at elevated temperatures (40 degrees C). This study provides important information for optimizing the application of sucrose monoesters to form colloidal dispersions in food and beverage products. (C) 2011 Elsevier Ltd. All rights reserved.