Formulation and heat stability of self-assembled O/W food-grade microemulsions formulated with bile salts or tween 80 as surfactants

Abstract

Recently, there has been a growing interest in developing food-grade (F-G) microemulsions (MEMs) with potential applications in the food industry, such as a green solvent for extracting bioactive compounds or as a vehicle to solubilize low-polar bioactive compounds. Therefore, this work aimed to create F-G MEMs using a low-energy titration method, bile salt or tween 80 as surfactants, and F-G ingredients like acetic acid, olive oil, limonene, and coconut oil. For this purpose, 56 formulations were assessed, from which 14 created oil-in-water (O/W) one-phase Winsor type IV microemulsions. All the F-G MEMs were transparent (turbidity ≤ 0.17 %) with watery densities (1.00 – 1.034 g/cm³) and viscosities (∼1–5 mPa･s). The MEMs formulated with bile salts had a neutral pH (7.75) and could only solubilize small lipids like limonene (2 % maximum). In contrast, those MEMs using tween 80 as surfactant showed an acidic pH (∼1–5.9) and could solubilize triglyceride-based lipids (0.2 % maximum) and limonene (4 % maximum) at surfactant concentrations as low as 1 %. The F-G MEMs were successfully created using the low-energy titration method, although the time to form each MEM varied significantly. The MEMs formulated with bile salts were self-assembled in ∼12 h, whereas the formation of MEMs with tween 80 required up to 28 days. Nevertheless, once the MEMs were formed, they presented extraordinary stability to high-shear stirring (15,600 rpm for 5 min) and heating (up to 150 ºC) without turning cloudy or showing a phase separation.